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FFmpeg 4.3 音视频-多路H265监控录放C++开发十三：将AVFrame转换成AVPacket。视频编码原理.编码相关api

article 2024/11/13 18:23:17

前提：

从前面的学习我们知道 AVFrame中是最原始的 视频数据，这一节开始我们需要将这个最原始的视频数据 压缩成 AVPacket数据，

我们前面，将YUV数据或者 RGBA 数据装进入了 AVFrame里面，并且在SDL中显示。

也就是说：对于安防项目来说，我们将原始从摄像头数据(YUV,RGB)转换成 AVFrame后，可以直接显示出来。但是如果我们将要数据存储，则要将 AVFrame转成  AVPacket.

视频编码 以及原理

从摄像头得到原始数据 ---- > 像素格式转换---->编码 ------>封装

编码的原因很好理解，YUV数据太大了，我们要编码成 h264，h265 等较小的格式

背后的原理是这样，一个YUV视频是由一张一张YUV图片组成的。

帧内压缩：

我们将一张YUV图片，假设是 1280x728大小的，我们将其划分成16x16的大小，总有一些像素点是一样的，或者接近的，例如下图：

帧间压缩：

假设上述图片是YUV 的第一张图片，第二帧图片是师爷 在讲话，那么第二帧图片可能只是嘴巴变化了一下，那么我们参考第一张图片，去存储第二张图片，就只用存储第二章图片 和 第一张图片不同的地方就好。。在还原的时候，参考第一张图片和差异，通过算法还原，这就叫做帧间压缩

我们这一节将 AVFrame转成 AVPacket，实际上就是编码的过程，

AVPacket 重要函数以及重要结构体成员

FFmpeg存放压缩后的音视频数据的结构体：AVPacket简介，结构体，函数-CSDN博客

从avframe 变成 avpacket 也就是编码，编码相关API

1.查找编码器

/**
 * Find a registered encoder with a matching codec ID.
 *
 * @param id AVCodecID of the requested encoder
 * @return An encoder if one was found, NULL otherwise.
 */


const AVCodec *avcodec_find_encoder(enum AVCodecID id);

如果参数 是 AVCodecID ，那么对应的值如下，重要的为    

AV_CODEC_ID_H264, 

#define AV_CODEC_ID_H265 AV_CODEC_ID_HEVC

enum AVCodecID {
    AV_CODEC_ID_NONE,

    /* video codecs */
    AV_CODEC_ID_MPEG1VIDEO,
    AV_CODEC_ID_MPEG2VIDEO, ///< preferred ID for MPEG-1/2 video decoding
    AV_CODEC_ID_H261,
    AV_CODEC_ID_H263,
    AV_CODEC_ID_RV10,
    AV_CODEC_ID_RV20,
    AV_CODEC_ID_MJPEG,
    AV_CODEC_ID_MJPEGB,
    AV_CODEC_ID_LJPEG,
    AV_CODEC_ID_SP5X,
    AV_CODEC_ID_JPEGLS,
    AV_CODEC_ID_MPEG4,
    AV_CODEC_ID_RAWVIDEO,
    AV_CODEC_ID_MSMPEG4V1,
    AV_CODEC_ID_MSMPEG4V2,
    AV_CODEC_ID_MSMPEG4V3,
    AV_CODEC_ID_WMV1,
    AV_CODEC_ID_WMV2,
    AV_CODEC_ID_H263P,
    AV_CODEC_ID_H263I,
    AV_CODEC_ID_FLV1,
    AV_CODEC_ID_SVQ1,
    AV_CODEC_ID_SVQ3,
    AV_CODEC_ID_DVVIDEO,
    AV_CODEC_ID_HUFFYUV,
    AV_CODEC_ID_CYUV,
    AV_CODEC_ID_H264,
    AV_CODEC_ID_INDEO3,
    AV_CODEC_ID_VP3,
    AV_CODEC_ID_THEORA,
    AV_CODEC_ID_ASV1,
    AV_CODEC_ID_ASV2,
    AV_CODEC_ID_FFV1,
    AV_CODEC_ID_4XM,
    AV_CODEC_ID_VCR1,
    AV_CODEC_ID_CLJR,
    AV_CODEC_ID_MDEC,
    AV_CODEC_ID_ROQ,
    AV_CODEC_ID_INTERPLAY_VIDEO,
    AV_CODEC_ID_XAN_WC3,
    AV_CODEC_ID_XAN_WC4,
    AV_CODEC_ID_RPZA,
    AV_CODEC_ID_CINEPAK,
    AV_CODEC_ID_WS_VQA,
    AV_CODEC_ID_MSRLE,
    AV_CODEC_ID_MSVIDEO1,
    AV_CODEC_ID_IDCIN,
    AV_CODEC_ID_8BPS,
    AV_CODEC_ID_SMC,
    AV_CODEC_ID_FLIC,
    AV_CODEC_ID_TRUEMOTION1,
    AV_CODEC_ID_VMDVIDEO,
    AV_CODEC_ID_MSZH,
    AV_CODEC_ID_ZLIB,
    AV_CODEC_ID_QTRLE,
    AV_CODEC_ID_TSCC,
    AV_CODEC_ID_ULTI,
    AV_CODEC_ID_QDRAW,
    AV_CODEC_ID_VIXL,
    AV_CODEC_ID_QPEG,
    AV_CODEC_ID_PNG,
    AV_CODEC_ID_PPM,
    AV_CODEC_ID_PBM,
    AV_CODEC_ID_PGM,
    AV_CODEC_ID_PGMYUV,
    AV_CODEC_ID_PAM,
    AV_CODEC_ID_FFVHUFF,
    AV_CODEC_ID_RV30,
    AV_CODEC_ID_RV40,
    AV_CODEC_ID_VC1,
    AV_CODEC_ID_WMV3,
    AV_CODEC_ID_LOCO,
    AV_CODEC_ID_WNV1,
    AV_CODEC_ID_AASC,
    AV_CODEC_ID_INDEO2,
    AV_CODEC_ID_FRAPS,
    AV_CODEC_ID_TRUEMOTION2,
    AV_CODEC_ID_BMP,
    AV_CODEC_ID_CSCD,
    AV_CODEC_ID_MMVIDEO,
    AV_CODEC_ID_ZMBV,
    AV_CODEC_ID_AVS,
    AV_CODEC_ID_SMACKVIDEO,
    AV_CODEC_ID_NUV,
    AV_CODEC_ID_KMVC,
    AV_CODEC_ID_FLASHSV,
    AV_CODEC_ID_CAVS,
    AV_CODEC_ID_JPEG2000,
    AV_CODEC_ID_VMNC,
    AV_CODEC_ID_VP5,
    AV_CODEC_ID_VP6,
    AV_CODEC_ID_VP6F,
    AV_CODEC_ID_TARGA,
    AV_CODEC_ID_DSICINVIDEO,
    AV_CODEC_ID_TIERTEXSEQVIDEO,
    AV_CODEC_ID_TIFF,
    AV_CODEC_ID_GIF,
    AV_CODEC_ID_DXA,
    AV_CODEC_ID_DNXHD,
    AV_CODEC_ID_THP,
    AV_CODEC_ID_SGI,
    AV_CODEC_ID_C93,
    AV_CODEC_ID_BETHSOFTVID,
    AV_CODEC_ID_PTX,
    AV_CODEC_ID_TXD,
    AV_CODEC_ID_VP6A,
    AV_CODEC_ID_AMV,
    AV_CODEC_ID_VB,
    AV_CODEC_ID_PCX,
    AV_CODEC_ID_SUNRAST,
    AV_CODEC_ID_INDEO4,
    AV_CODEC_ID_INDEO5,
    AV_CODEC_ID_MIMIC,
    AV_CODEC_ID_RL2,
    AV_CODEC_ID_ESCAPE124,
    AV_CODEC_ID_DIRAC,
    AV_CODEC_ID_BFI,
    AV_CODEC_ID_CMV,
    AV_CODEC_ID_MOTIONPIXELS,
    AV_CODEC_ID_TGV,
    AV_CODEC_ID_TGQ,
    AV_CODEC_ID_TQI,
    AV_CODEC_ID_AURA,
    AV_CODEC_ID_AURA2,
    AV_CODEC_ID_V210X,
    AV_CODEC_ID_TMV,
    AV_CODEC_ID_V210,
    AV_CODEC_ID_DPX,
    AV_CODEC_ID_MAD,
    AV_CODEC_ID_FRWU,
    AV_CODEC_ID_FLASHSV2,
    AV_CODEC_ID_CDGRAPHICS,
    AV_CODEC_ID_R210,
    AV_CODEC_ID_ANM,
    AV_CODEC_ID_BINKVIDEO,
    AV_CODEC_ID_IFF_ILBM,
#define AV_CODEC_ID_IFF_BYTERUN1 AV_CODEC_ID_IFF_ILBM
    AV_CODEC_ID_KGV1,
    AV_CODEC_ID_YOP,
    AV_CODEC_ID_VP8,
    AV_CODEC_ID_PICTOR,
    AV_CODEC_ID_ANSI,
    AV_CODEC_ID_A64_MULTI,
    AV_CODEC_ID_A64_MULTI5,
    AV_CODEC_ID_R10K,
    AV_CODEC_ID_MXPEG,
    AV_CODEC_ID_LAGARITH,
    AV_CODEC_ID_PRORES,
    AV_CODEC_ID_JV,
    AV_CODEC_ID_DFA,
    AV_CODEC_ID_WMV3IMAGE,
    AV_CODEC_ID_VC1IMAGE,
    AV_CODEC_ID_UTVIDEO,
    AV_CODEC_ID_BMV_VIDEO,
    AV_CODEC_ID_VBLE,
    AV_CODEC_ID_DXTORY,
    AV_CODEC_ID_V410,
    AV_CODEC_ID_XWD,
    AV_CODEC_ID_CDXL,
    AV_CODEC_ID_XBM,
    AV_CODEC_ID_ZEROCODEC,
    AV_CODEC_ID_MSS1,
    AV_CODEC_ID_MSA1,
    AV_CODEC_ID_TSCC2,
    AV_CODEC_ID_MTS2,
    AV_CODEC_ID_CLLC,
    AV_CODEC_ID_MSS2,
    AV_CODEC_ID_VP9,
    AV_CODEC_ID_AIC,
    AV_CODEC_ID_ESCAPE130,
    AV_CODEC_ID_G2M,
    AV_CODEC_ID_WEBP,
    AV_CODEC_ID_HNM4_VIDEO,
    AV_CODEC_ID_HEVC,
#define AV_CODEC_ID_H265 AV_CODEC_ID_HEVC
    AV_CODEC_ID_FIC,
    AV_CODEC_ID_ALIAS_PIX,
    AV_CODEC_ID_BRENDER_PIX,
    AV_CODEC_ID_PAF_VIDEO,
    AV_CODEC_ID_EXR,
    AV_CODEC_ID_VP7,
    AV_CODEC_ID_SANM,
    AV_CODEC_ID_SGIRLE,
    AV_CODEC_ID_MVC1,
    AV_CODEC_ID_MVC2,
    AV_CODEC_ID_HQX,
    AV_CODEC_ID_TDSC,
    AV_CODEC_ID_HQ_HQA,
    AV_CODEC_ID_HAP,
    AV_CODEC_ID_DDS,
    AV_CODEC_ID_DXV,
    AV_CODEC_ID_SCREENPRESSO,
    AV_CODEC_ID_RSCC,
    AV_CODEC_ID_AVS2,

    AV_CODEC_ID_Y41P = 0x8000,
    AV_CODEC_ID_AVRP,
    AV_CODEC_ID_012V,
    AV_CODEC_ID_AVUI,
    AV_CODEC_ID_AYUV,
    AV_CODEC_ID_TARGA_Y216,
    AV_CODEC_ID_V308,
    AV_CODEC_ID_V408,
    AV_CODEC_ID_YUV4,
    AV_CODEC_ID_AVRN,
    AV_CODEC_ID_CPIA,
    AV_CODEC_ID_XFACE,
    AV_CODEC_ID_SNOW,
    AV_CODEC_ID_SMVJPEG,
    AV_CODEC_ID_APNG,
    AV_CODEC_ID_DAALA,
    AV_CODEC_ID_CFHD,
    AV_CODEC_ID_TRUEMOTION2RT,
    AV_CODEC_ID_M101,
    AV_CODEC_ID_MAGICYUV,
    AV_CODEC_ID_SHEERVIDEO,
    AV_CODEC_ID_YLC,
    AV_CODEC_ID_PSD,
    AV_CODEC_ID_PIXLET,
    AV_CODEC_ID_SPEEDHQ,
    AV_CODEC_ID_FMVC,
    AV_CODEC_ID_SCPR,
    AV_CODEC_ID_CLEARVIDEO,
    AV_CODEC_ID_XPM,
    AV_CODEC_ID_AV1,
    AV_CODEC_ID_BITPACKED,
    AV_CODEC_ID_MSCC,
    AV_CODEC_ID_SRGC,
    AV_CODEC_ID_SVG,
    AV_CODEC_ID_GDV,
    AV_CODEC_ID_FITS,
    AV_CODEC_ID_IMM4,
    AV_CODEC_ID_PROSUMER,
    AV_CODEC_ID_MWSC,
    AV_CODEC_ID_WCMV,
    AV_CODEC_ID_RASC,
    AV_CODEC_ID_HYMT,
    AV_CODEC_ID_ARBC,
    AV_CODEC_ID_AGM,
    AV_CODEC_ID_LSCR,
    AV_CODEC_ID_VP4,
    AV_CODEC_ID_IMM5,
    AV_CODEC_ID_MVDV,
    AV_CODEC_ID_MVHA,
    AV_CODEC_ID_CDTOONS,
    AV_CODEC_ID_MV30,
    AV_CODEC_ID_NOTCHLC,
    AV_CODEC_ID_PFM,

    /* various PCM "codecs" */
    AV_CODEC_ID_FIRST_AUDIO = 0x10000,     ///< A dummy id pointing at the start of audio codecs
    AV_CODEC_ID_PCM_S16LE = 0x10000,
    AV_CODEC_ID_PCM_S16BE,
    AV_CODEC_ID_PCM_U16LE,
    AV_CODEC_ID_PCM_U16BE,
    AV_CODEC_ID_PCM_S8,
    AV_CODEC_ID_PCM_U8,
    AV_CODEC_ID_PCM_MULAW,
    AV_CODEC_ID_PCM_ALAW,
    AV_CODEC_ID_PCM_S32LE,
    AV_CODEC_ID_PCM_S32BE,
    AV_CODEC_ID_PCM_U32LE,
    AV_CODEC_ID_PCM_U32BE,
    AV_CODEC_ID_PCM_S24LE,
    AV_CODEC_ID_PCM_S24BE,
    AV_CODEC_ID_PCM_U24LE,
    AV_CODEC_ID_PCM_U24BE,
    AV_CODEC_ID_PCM_S24DAUD,
    AV_CODEC_ID_PCM_ZORK,
    AV_CODEC_ID_PCM_S16LE_PLANAR,
    AV_CODEC_ID_PCM_DVD,
    AV_CODEC_ID_PCM_F32BE,
    AV_CODEC_ID_PCM_F32LE,
    AV_CODEC_ID_PCM_F64BE,
    AV_CODEC_ID_PCM_F64LE,
    AV_CODEC_ID_PCM_BLURAY,
    AV_CODEC_ID_PCM_LXF,
    AV_CODEC_ID_S302M,
    AV_CODEC_ID_PCM_S8_PLANAR,
    AV_CODEC_ID_PCM_S24LE_PLANAR,
    AV_CODEC_ID_PCM_S32LE_PLANAR,
    AV_CODEC_ID_PCM_S16BE_PLANAR,

    AV_CODEC_ID_PCM_S64LE = 0x10800,
    AV_CODEC_ID_PCM_S64BE,
    AV_CODEC_ID_PCM_F16LE,
    AV_CODEC_ID_PCM_F24LE,
    AV_CODEC_ID_PCM_VIDC,

    /* various ADPCM codecs */
    AV_CODEC_ID_ADPCM_IMA_QT = 0x11000,
    AV_CODEC_ID_ADPCM_IMA_WAV,
    AV_CODEC_ID_ADPCM_IMA_DK3,
    AV_CODEC_ID_ADPCM_IMA_DK4,
    AV_CODEC_ID_ADPCM_IMA_WS,
    AV_CODEC_ID_ADPCM_IMA_SMJPEG,
    AV_CODEC_ID_ADPCM_MS,
    AV_CODEC_ID_ADPCM_4XM,
    AV_CODEC_ID_ADPCM_XA,
    AV_CODEC_ID_ADPCM_ADX,
    AV_CODEC_ID_ADPCM_EA,
    AV_CODEC_ID_ADPCM_G726,
    AV_CODEC_ID_ADPCM_CT,
    AV_CODEC_ID_ADPCM_SWF,
    AV_CODEC_ID_ADPCM_YAMAHA,
    AV_CODEC_ID_ADPCM_SBPRO_4,
    AV_CODEC_ID_ADPCM_SBPRO_3,
    AV_CODEC_ID_ADPCM_SBPRO_2,
    AV_CODEC_ID_ADPCM_THP,
    AV_CODEC_ID_ADPCM_IMA_AMV,
    AV_CODEC_ID_ADPCM_EA_R1,
    AV_CODEC_ID_ADPCM_EA_R3,
    AV_CODEC_ID_ADPCM_EA_R2,
    AV_CODEC_ID_ADPCM_IMA_EA_SEAD,
    AV_CODEC_ID_ADPCM_IMA_EA_EACS,
    AV_CODEC_ID_ADPCM_EA_XAS,
    AV_CODEC_ID_ADPCM_EA_MAXIS_XA,
    AV_CODEC_ID_ADPCM_IMA_ISS,
    AV_CODEC_ID_ADPCM_G722,
    AV_CODEC_ID_ADPCM_IMA_APC,
    AV_CODEC_ID_ADPCM_VIMA,

    AV_CODEC_ID_ADPCM_AFC = 0x11800,
    AV_CODEC_ID_ADPCM_IMA_OKI,
    AV_CODEC_ID_ADPCM_DTK,
    AV_CODEC_ID_ADPCM_IMA_RAD,
    AV_CODEC_ID_ADPCM_G726LE,
    AV_CODEC_ID_ADPCM_THP_LE,
    AV_CODEC_ID_ADPCM_PSX,
    AV_CODEC_ID_ADPCM_AICA,
    AV_CODEC_ID_ADPCM_IMA_DAT4,
    AV_CODEC_ID_ADPCM_MTAF,
    AV_CODEC_ID_ADPCM_AGM,
    AV_CODEC_ID_ADPCM_ARGO,
    AV_CODEC_ID_ADPCM_IMA_SSI,
    AV_CODEC_ID_ADPCM_ZORK,
    AV_CODEC_ID_ADPCM_IMA_APM,
    AV_CODEC_ID_ADPCM_IMA_ALP,
    AV_CODEC_ID_ADPCM_IMA_MTF,
    AV_CODEC_ID_ADPCM_IMA_CUNNING,

    /* AMR */
    AV_CODEC_ID_AMR_NB = 0x12000,
    AV_CODEC_ID_AMR_WB,

    /* RealAudio codecs*/
    AV_CODEC_ID_RA_144 = 0x13000,
    AV_CODEC_ID_RA_288,

    /* various DPCM codecs */
    AV_CODEC_ID_ROQ_DPCM = 0x14000,
    AV_CODEC_ID_INTERPLAY_DPCM,
    AV_CODEC_ID_XAN_DPCM,
    AV_CODEC_ID_SOL_DPCM,

    AV_CODEC_ID_SDX2_DPCM = 0x14800,
    AV_CODEC_ID_GREMLIN_DPCM,
    AV_CODEC_ID_DERF_DPCM,

    /* audio codecs */
    AV_CODEC_ID_MP2 = 0x15000,
    AV_CODEC_ID_MP3, ///< preferred ID for decoding MPEG audio layer 1, 2 or 3
    AV_CODEC_ID_AAC,
    AV_CODEC_ID_AC3,
    AV_CODEC_ID_DTS,
    AV_CODEC_ID_VORBIS,
    AV_CODEC_ID_DVAUDIO,
    AV_CODEC_ID_WMAV1,
    AV_CODEC_ID_WMAV2,
    AV_CODEC_ID_MACE3,
    AV_CODEC_ID_MACE6,
    AV_CODEC_ID_VMDAUDIO,
    AV_CODEC_ID_FLAC,
    AV_CODEC_ID_MP3ADU,
    AV_CODEC_ID_MP3ON4,
    AV_CODEC_ID_SHORTEN,
    AV_CODEC_ID_ALAC,
    AV_CODEC_ID_WESTWOOD_SND1,
    AV_CODEC_ID_GSM, ///< as in Berlin toast format
    AV_CODEC_ID_QDM2,
    AV_CODEC_ID_COOK,
    AV_CODEC_ID_TRUESPEECH,
    AV_CODEC_ID_TTA,
    AV_CODEC_ID_SMACKAUDIO,
    AV_CODEC_ID_QCELP,
    AV_CODEC_ID_WAVPACK,
    AV_CODEC_ID_DSICINAUDIO,
    AV_CODEC_ID_IMC,
    AV_CODEC_ID_MUSEPACK7,
    AV_CODEC_ID_MLP,
    AV_CODEC_ID_GSM_MS, /* as found in WAV */
    AV_CODEC_ID_ATRAC3,
    AV_CODEC_ID_APE,
    AV_CODEC_ID_NELLYMOSER,
    AV_CODEC_ID_MUSEPACK8,
    AV_CODEC_ID_SPEEX,
    AV_CODEC_ID_WMAVOICE,
    AV_CODEC_ID_WMAPRO,
    AV_CODEC_ID_WMALOSSLESS,
    AV_CODEC_ID_ATRAC3P,
    AV_CODEC_ID_EAC3,
    AV_CODEC_ID_SIPR,
    AV_CODEC_ID_MP1,
    AV_CODEC_ID_TWINVQ,
    AV_CODEC_ID_TRUEHD,
    AV_CODEC_ID_MP4ALS,
    AV_CODEC_ID_ATRAC1,
    AV_CODEC_ID_BINKAUDIO_RDFT,
    AV_CODEC_ID_BINKAUDIO_DCT,
    AV_CODEC_ID_AAC_LATM,
    AV_CODEC_ID_QDMC,
    AV_CODEC_ID_CELT,
    AV_CODEC_ID_G723_1,
    AV_CODEC_ID_G729,
    AV_CODEC_ID_8SVX_EXP,
    AV_CODEC_ID_8SVX_FIB,
    AV_CODEC_ID_BMV_AUDIO,
    AV_CODEC_ID_RALF,
    AV_CODEC_ID_IAC,
    AV_CODEC_ID_ILBC,
    AV_CODEC_ID_OPUS,
    AV_CODEC_ID_COMFORT_NOISE,
    AV_CODEC_ID_TAK,
    AV_CODEC_ID_METASOUND,
    AV_CODEC_ID_PAF_AUDIO,
    AV_CODEC_ID_ON2AVC,
    AV_CODEC_ID_DSS_SP,
    AV_CODEC_ID_CODEC2,

    AV_CODEC_ID_FFWAVESYNTH = 0x15800,
    AV_CODEC_ID_SONIC,
    AV_CODEC_ID_SONIC_LS,
    AV_CODEC_ID_EVRC,
    AV_CODEC_ID_SMV,
    AV_CODEC_ID_DSD_LSBF,
    AV_CODEC_ID_DSD_MSBF,
    AV_CODEC_ID_DSD_LSBF_PLANAR,
    AV_CODEC_ID_DSD_MSBF_PLANAR,
    AV_CODEC_ID_4GV,
    AV_CODEC_ID_INTERPLAY_ACM,
    AV_CODEC_ID_XMA1,
    AV_CODEC_ID_XMA2,
    AV_CODEC_ID_DST,
    AV_CODEC_ID_ATRAC3AL,
    AV_CODEC_ID_ATRAC3PAL,
    AV_CODEC_ID_DOLBY_E,
    AV_CODEC_ID_APTX,
    AV_CODEC_ID_APTX_HD,
    AV_CODEC_ID_SBC,
    AV_CODEC_ID_ATRAC9,
    AV_CODEC_ID_HCOM,
    AV_CODEC_ID_ACELP_KELVIN,
    AV_CODEC_ID_MPEGH_3D_AUDIO,
    AV_CODEC_ID_SIREN,
    AV_CODEC_ID_HCA,

    /* subtitle codecs */
    AV_CODEC_ID_FIRST_SUBTITLE = 0x17000,          ///< A dummy ID pointing at the start of subtitle codecs.
    AV_CODEC_ID_DVD_SUBTITLE = 0x17000,
    AV_CODEC_ID_DVB_SUBTITLE,
    AV_CODEC_ID_TEXT,  ///< raw UTF-8 text
    AV_CODEC_ID_XSUB,
    AV_CODEC_ID_SSA,
    AV_CODEC_ID_MOV_TEXT,
    AV_CODEC_ID_HDMV_PGS_SUBTITLE,
    AV_CODEC_ID_DVB_TELETEXT,
    AV_CODEC_ID_SRT,

    AV_CODEC_ID_MICRODVD   = 0x17800,
    AV_CODEC_ID_EIA_608,
    AV_CODEC_ID_JACOSUB,
    AV_CODEC_ID_SAMI,
    AV_CODEC_ID_REALTEXT,
    AV_CODEC_ID_STL,
    AV_CODEC_ID_SUBVIEWER1,
    AV_CODEC_ID_SUBVIEWER,
    AV_CODEC_ID_SUBRIP,
    AV_CODEC_ID_WEBVTT,
    AV_CODEC_ID_MPL2,
    AV_CODEC_ID_VPLAYER,
    AV_CODEC_ID_PJS,
    AV_CODEC_ID_ASS,
    AV_CODEC_ID_HDMV_TEXT_SUBTITLE,
    AV_CODEC_ID_TTML,
    AV_CODEC_ID_ARIB_CAPTION,

    /* other specific kind of codecs (generally used for attachments) */
    AV_CODEC_ID_FIRST_UNKNOWN = 0x18000,           ///< A dummy ID pointing at the start of various fake codecs.
    AV_CODEC_ID_TTF = 0x18000,

    AV_CODEC_ID_SCTE_35, ///< Contain timestamp estimated through PCR of program stream.
    AV_CODEC_ID_EPG,
    AV_CODEC_ID_BINTEXT    = 0x18800,
    AV_CODEC_ID_XBIN,
    AV_CODEC_ID_IDF,
    AV_CODEC_ID_OTF,
    AV_CODEC_ID_SMPTE_KLV,
    AV_CODEC_ID_DVD_NAV,
    AV_CODEC_ID_TIMED_ID3,
    AV_CODEC_ID_BIN_DATA,


    AV_CODEC_ID_PROBE = 0x19000, ///< codec_id is not known (like AV_CODEC_ID_NONE) but lavf should attempt to identify it

    AV_CODEC_ID_MPEG2TS = 0x20000, /**< _FAKE_ codec to indicate a raw MPEG-2 TS
                                * stream (only used by libavformat) */
    AV_CODEC_ID_MPEG4SYSTEMS = 0x20001, /**< _FAKE_ codec to indicate a MPEG-4 Systems
                                * stream (only used by libavformat) */
    AV_CODEC_ID_FFMETADATA = 0x21000,   ///< Dummy codec for streams containing only metadata information.
    AV_CODEC_ID_WRAPPED_AVFRAME = 0x21001, ///< Passthrough codec, AVFrames wrapped in AVPacket
};

/**
 * Find a registered encoder with the specified name.
 *
 * @param name name of the requested encoder
 * @return An encoder if one was found, NULL otherwise.
 */
 


const AVCodec *avcodec_find_encoder_by_name(const char *name);


 

如果是通过字符查找对应的编码器/解码器，我们怎么知道这个字符是啥编码器呢？

libavcodec/allcodecs.c中开头定义了很多支编解码结构体;如:

可以查看具体的某一个，当然有些只是定义，ffmpeg并没有实现，如果要实现需要

/*
 * Provide registration of all codecs, parsers and bitstream filters for libavcodec.
 * Copyright (c) 2002 Fabrice Bellard
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * Provide registration of all codecs, parsers and bitstream filters for libavcodec.
 */

#include <stdint.h>
#include <string.h>

#include "config.h"
#include "config_components.h"
#include "libavutil/thread.h"
#include "codec.h"
#include "codec_id.h"
#include "codec_internal.h"

extern const FFCodec ff_a64multi_encoder;
extern const FFCodec ff_a64multi5_encoder;
extern const FFCodec ff_aasc_decoder;
extern const FFCodec ff_aic_decoder;
extern const FFCodec ff_alias_pix_encoder;
extern const FFCodec ff_alias_pix_decoder;
extern const FFCodec ff_agm_decoder;
extern const FFCodec ff_amv_encoder;
extern const FFCodec ff_amv_decoder;
extern const FFCodec ff_anm_decoder;
extern const FFCodec ff_ansi_decoder;
extern const FFCodec ff_apng_encoder;
extern const FFCodec ff_apng_decoder;
extern const FFCodec ff_arbc_decoder;
extern const FFCodec ff_argo_decoder;
extern const FFCodec ff_asv1_encoder;
extern const FFCodec ff_asv1_decoder;
extern const FFCodec ff_asv2_encoder;
extern const FFCodec ff_asv2_decoder;
extern const FFCodec ff_aura_decoder;
extern const FFCodec ff_aura2_decoder;
extern const FFCodec ff_avrp_encoder;
extern const FFCodec ff_avrp_decoder;
extern const FFCodec ff_avrn_decoder;
extern const FFCodec ff_avs_decoder;
extern const FFCodec ff_avui_encoder;
extern const FFCodec ff_avui_decoder;
#if FF_API_AYUV_CODECID
extern const FFCodec ff_ayuv_encoder;
extern const FFCodec ff_ayuv_decoder;
#endif
extern const FFCodec ff_bethsoftvid_decoder;
extern const FFCodec ff_bfi_decoder;
extern const FFCodec ff_bink_decoder;
extern const FFCodec ff_bitpacked_decoder;
extern const FFCodec ff_bitpacked_encoder;
extern const FFCodec ff_bmp_encoder;
extern const FFCodec ff_bmp_decoder;
extern const FFCodec ff_bmv_video_decoder;
extern const FFCodec ff_brender_pix_decoder;
extern const FFCodec ff_c93_decoder;
extern const FFCodec ff_cavs_decoder;
extern const FFCodec ff_cdgraphics_decoder;
extern const FFCodec ff_cdtoons_decoder;
extern const FFCodec ff_cdxl_decoder;
extern const FFCodec ff_cfhd_encoder;
extern const FFCodec ff_cfhd_decoder;
extern const FFCodec ff_cinepak_encoder;
extern const FFCodec ff_cinepak_decoder;
extern const FFCodec ff_clearvideo_decoder;
extern const FFCodec ff_cljr_encoder;
extern const FFCodec ff_cljr_decoder;
extern const FFCodec ff_cllc_decoder;
extern const FFCodec ff_comfortnoise_encoder;
extern const FFCodec ff_comfortnoise_decoder;
extern const FFCodec ff_cpia_decoder;
extern const FFCodec ff_cri_decoder;
extern const FFCodec ff_cscd_decoder;
extern const FFCodec ff_cyuv_decoder;
extern const FFCodec ff_dds_decoder;
extern const FFCodec ff_dfa_decoder;
extern const FFCodec ff_dirac_decoder;
extern const FFCodec ff_dnxhd_encoder;
extern const FFCodec ff_dnxhd_decoder;
extern const FFCodec ff_dpx_encoder;
extern const FFCodec ff_dpx_decoder;
extern const FFCodec ff_dsicinvideo_decoder;
extern const FFCodec ff_dvaudio_decoder;
extern const FFCodec ff_dvvideo_encoder;
extern const FFCodec ff_dvvideo_decoder;
extern const FFCodec ff_dxa_decoder;
extern const FFCodec ff_dxtory_decoder;
extern const FFCodec ff_dxv_decoder;
extern const FFCodec ff_eacmv_decoder;
extern const FFCodec ff_eamad_decoder;
extern const FFCodec ff_eatgq_decoder;
extern const FFCodec ff_eatgv_decoder;
extern const FFCodec ff_eatqi_decoder;
extern const FFCodec ff_eightbps_decoder;
extern const FFCodec ff_eightsvx_exp_decoder;
extern const FFCodec ff_eightsvx_fib_decoder;
extern const FFCodec ff_escape124_decoder;
extern const FFCodec ff_escape130_decoder;
extern const FFCodec ff_exr_encoder;
extern const FFCodec ff_exr_decoder;
extern const FFCodec ff_ffv1_encoder;
extern const FFCodec ff_ffv1_decoder;
extern const FFCodec ff_ffvhuff_encoder;
extern const FFCodec ff_ffvhuff_decoder;
extern const FFCodec ff_fic_decoder;
extern const FFCodec ff_fits_encoder;
extern const FFCodec ff_fits_decoder;
extern const FFCodec ff_flashsv_encoder;
extern const FFCodec ff_flashsv_decoder;
extern const FFCodec ff_flashsv2_encoder;
extern const FFCodec ff_flashsv2_decoder;
extern const FFCodec ff_flic_decoder;
extern const FFCodec ff_flv_encoder;
extern const FFCodec ff_flv_decoder;
extern const FFCodec ff_fmvc_decoder;
extern const FFCodec ff_fourxm_decoder;
extern const FFCodec ff_fraps_decoder;
extern const FFCodec ff_frwu_decoder;
extern const FFCodec ff_g2m_decoder;
extern const FFCodec ff_gdv_decoder;
extern const FFCodec ff_gem_decoder;
extern const FFCodec ff_gif_encoder;
extern const FFCodec ff_gif_decoder;
extern const FFCodec ff_h261_encoder;
extern const FFCodec ff_h261_decoder;
extern const FFCodec ff_h263_encoder;
extern const FFCodec ff_h263_decoder;
extern const FFCodec ff_h263i_decoder;
extern const FFCodec ff_h263p_encoder;
extern const FFCodec ff_h263p_decoder;
extern const FFCodec ff_h263_v4l2m2m_decoder;
extern const FFCodec ff_h264_decoder;
extern const FFCodec ff_h264_crystalhd_decoder;
extern const FFCodec ff_h264_v4l2m2m_decoder;
extern const FFCodec ff_h264_mediacodec_decoder;
extern const FFCodec ff_h264_mediacodec_encoder;
extern const FFCodec ff_h264_mmal_decoder;
extern const FFCodec ff_h264_qsv_decoder;
extern const FFCodec ff_h264_rkmpp_decoder;
extern const FFCodec ff_hap_encoder;
extern const FFCodec ff_hap_decoder;
extern const FFCodec ff_hevc_decoder;
extern const FFCodec ff_hevc_qsv_decoder;
extern const FFCodec ff_hevc_rkmpp_decoder;
extern const FFCodec ff_hevc_v4l2m2m_decoder;
extern const FFCodec ff_hnm4_video_decoder;
extern const FFCodec ff_hq_hqa_decoder;
extern const FFCodec ff_hqx_decoder;
extern const FFCodec ff_huffyuv_encoder;
extern const FFCodec ff_huffyuv_decoder;
extern const FFCodec ff_hymt_decoder;
extern const FFCodec ff_idcin_decoder;
extern const FFCodec ff_iff_ilbm_decoder;
extern const FFCodec ff_imm4_decoder;
extern const FFCodec ff_imm5_decoder;
extern const FFCodec ff_indeo2_decoder;
extern const FFCodec ff_indeo3_decoder;
extern const FFCodec ff_indeo4_decoder;
extern const FFCodec ff_indeo5_decoder;
extern const FFCodec ff_interplay_video_decoder;
extern const FFCodec ff_ipu_decoder;
extern const FFCodec ff_jpeg2000_encoder;
extern const FFCodec ff_jpeg2000_decoder;
extern const FFCodec ff_jpegls_encoder;
extern const FFCodec ff_jpegls_decoder;
extern const FFCodec ff_jv_decoder;
extern const FFCodec ff_kgv1_decoder;
extern const FFCodec ff_kmvc_decoder;
extern const FFCodec ff_lagarith_decoder;
extern const FFCodec ff_ljpeg_encoder;
extern const FFCodec ff_loco_decoder;
extern const FFCodec ff_lscr_decoder;
extern const FFCodec ff_m101_decoder;
extern const FFCodec ff_magicyuv_encoder;
extern const FFCodec ff_magicyuv_decoder;
extern const FFCodec ff_mdec_decoder;
extern const FFCodec ff_media100_decoder;
extern const FFCodec ff_mimic_decoder;
extern const FFCodec ff_mjpeg_encoder;
extern const FFCodec ff_mjpeg_decoder;
extern const FFCodec ff_mjpegb_decoder;
extern const FFCodec ff_mmvideo_decoder;
extern const FFCodec ff_mobiclip_decoder;
extern const FFCodec ff_motionpixels_decoder;
extern const FFCodec ff_mpeg1video_encoder;
extern const FFCodec ff_mpeg1video_decoder;
extern const FFCodec ff_mpeg2video_encoder;
extern const FFCodec ff_mpeg2video_decoder;
extern const FFCodec ff_mpeg4_encoder;
extern const FFCodec ff_mpeg4_decoder;
extern const FFCodec ff_mpeg4_crystalhd_decoder;
extern const FFCodec ff_mpeg4_v4l2m2m_decoder;
extern const FFCodec ff_mpeg4_mmal_decoder;
extern const FFCodec ff_mpegvideo_decoder;
extern const FFCodec ff_mpeg1_v4l2m2m_decoder;
extern const FFCodec ff_mpeg2_mmal_decoder;
extern const FFCodec ff_mpeg2_crystalhd_decoder;
extern const FFCodec ff_mpeg2_v4l2m2m_decoder;
extern const FFCodec ff_mpeg2_qsv_decoder;
extern const FFCodec ff_mpeg2_mediacodec_decoder;
extern const FFCodec ff_msa1_decoder;
extern const FFCodec ff_mscc_decoder;
extern const FFCodec ff_msmpeg4v1_decoder;
extern const FFCodec ff_msmpeg4v2_encoder;
extern const FFCodec ff_msmpeg4v2_decoder;
extern const FFCodec ff_msmpeg4v3_encoder;
extern const FFCodec ff_msmpeg4v3_decoder;
extern const FFCodec ff_msmpeg4_crystalhd_decoder;
extern const FFCodec ff_msp2_decoder;
extern const FFCodec ff_msrle_decoder;
extern const FFCodec ff_mss1_decoder;
extern const FFCodec ff_mss2_decoder;
extern const FFCodec ff_msvideo1_encoder;
extern const FFCodec ff_msvideo1_decoder;
extern const FFCodec ff_mszh_decoder;
extern const FFCodec ff_mts2_decoder;
extern const FFCodec ff_mv30_decoder;
extern const FFCodec ff_mvc1_decoder;
extern const FFCodec ff_mvc2_decoder;
extern const FFCodec ff_mvdv_decoder;
extern const FFCodec ff_mvha_decoder;
extern const FFCodec ff_mwsc_decoder;
extern const FFCodec ff_mxpeg_decoder;
extern const FFCodec ff_notchlc_decoder;
extern const FFCodec ff_nuv_decoder;
extern const FFCodec ff_paf_video_decoder;
extern const FFCodec ff_pam_encoder;
extern const FFCodec ff_pam_decoder;
extern const FFCodec ff_pbm_encoder;
extern const FFCodec ff_pbm_decoder;
extern const FFCodec ff_pcx_encoder;
extern const FFCodec ff_pcx_decoder;
extern const FFCodec ff_pfm_encoder;
extern const FFCodec ff_pfm_decoder;
extern const FFCodec ff_pgm_encoder;
extern const FFCodec ff_pgm_decoder;
extern const FFCodec ff_pgmyuv_encoder;
extern const FFCodec ff_pgmyuv_decoder;
extern const FFCodec ff_pgx_decoder;
extern const FFCodec ff_phm_encoder;
extern const FFCodec ff_phm_decoder;
extern const FFCodec ff_photocd_decoder;
extern const FFCodec ff_pictor_decoder;
extern const FFCodec ff_pixlet_decoder;
extern const FFCodec ff_png_encoder;
extern const FFCodec ff_png_decoder;
extern const FFCodec ff_ppm_encoder;
extern const FFCodec ff_ppm_decoder;
extern const FFCodec ff_prores_encoder;
extern const FFCodec ff_prores_decoder;
extern const FFCodec ff_prores_aw_encoder;
extern const FFCodec ff_prores_ks_encoder;
extern const FFCodec ff_prosumer_decoder;
extern const FFCodec ff_psd_decoder;
extern const FFCodec ff_ptx_decoder;
extern const FFCodec ff_qdraw_decoder;
extern const FFCodec ff_qoi_encoder;
extern const FFCodec ff_qoi_decoder;
extern const FFCodec ff_qpeg_decoder;
extern const FFCodec ff_qtrle_encoder;
extern const FFCodec ff_qtrle_decoder;
extern const FFCodec ff_r10k_encoder;
extern const FFCodec ff_r10k_decoder;
extern const FFCodec ff_r210_encoder;
extern const FFCodec ff_r210_decoder;
extern const FFCodec ff_rasc_decoder;
extern const FFCodec ff_rawvideo_encoder;
extern const FFCodec ff_rawvideo_decoder;
extern const FFCodec ff_rka_decoder;
extern const FFCodec ff_rl2_decoder;
extern const FFCodec ff_roq_encoder;
extern const FFCodec ff_roq_decoder;
extern const FFCodec ff_rpza_encoder;
extern const FFCodec ff_rpza_decoder;
extern const FFCodec ff_rscc_decoder;
extern const FFCodec ff_rv10_encoder;
extern const FFCodec ff_rv10_decoder;
extern const FFCodec ff_rv20_encoder;
extern const FFCodec ff_rv20_decoder;
extern const FFCodec ff_rv30_decoder;
extern const FFCodec ff_rv40_decoder;
extern const FFCodec ff_s302m_encoder;
extern const FFCodec ff_s302m_decoder;
extern const FFCodec ff_sanm_decoder;
extern const FFCodec ff_scpr_decoder;
extern const FFCodec ff_screenpresso_decoder;
extern const FFCodec ff_sga_decoder;
extern const FFCodec ff_sgi_encoder;
extern const FFCodec ff_sgi_decoder;
extern const FFCodec ff_sgirle_decoder;
extern const FFCodec ff_sheervideo_decoder;
extern const FFCodec ff_simbiosis_imx_decoder;
extern const FFCodec ff_smacker_decoder;
extern const FFCodec ff_smc_encoder;
extern const FFCodec ff_smc_decoder;
extern const FFCodec ff_smvjpeg_decoder;
extern const FFCodec ff_snow_encoder;
extern const FFCodec ff_snow_decoder;
extern const FFCodec ff_sp5x_decoder;
extern const FFCodec ff_speedhq_decoder;
extern const FFCodec ff_speedhq_encoder;
extern const FFCodec ff_speex_decoder;
extern const FFCodec ff_srgc_decoder;
extern const FFCodec ff_sunrast_encoder;
extern const FFCodec ff_sunrast_decoder;
extern const FFCodec ff_svq1_encoder;
extern const FFCodec ff_svq1_decoder;
extern const FFCodec ff_svq3_decoder;
extern const FFCodec ff_targa_encoder;
extern const FFCodec ff_targa_decoder;
extern const FFCodec ff_targa_y216_decoder;
extern const FFCodec ff_tdsc_decoder;
extern const FFCodec ff_theora_decoder;
extern const FFCodec ff_thp_decoder;
extern const FFCodec ff_tiertexseqvideo_decoder;
extern const FFCodec ff_tiff_encoder;
extern const FFCodec ff_tiff_decoder;
extern const FFCodec ff_tmv_decoder;
extern const FFCodec ff_truemotion1_decoder;
extern const FFCodec ff_truemotion2_decoder;
extern const FFCodec ff_truemotion2rt_decoder;
extern const FFCodec ff_tscc_decoder;
extern const FFCodec ff_tscc2_decoder;
extern const FFCodec ff_txd_decoder;
extern const FFCodec ff_ulti_decoder;
extern const FFCodec ff_utvideo_encoder;
extern const FFCodec ff_utvideo_decoder;
extern const FFCodec ff_v210_encoder;
extern const FFCodec ff_v210_decoder;
extern const FFCodec ff_v210x_decoder;
extern const FFCodec ff_v308_encoder;
extern const FFCodec ff_v308_decoder;
extern const FFCodec ff_v408_encoder;
extern const FFCodec ff_v408_decoder;
extern const FFCodec ff_v410_encoder;
extern const FFCodec ff_v410_decoder;
extern const FFCodec ff_vb_decoder;
extern const FFCodec ff_vbn_encoder;
extern const FFCodec ff_vbn_decoder;
extern const FFCodec ff_vble_decoder;
extern const FFCodec ff_vc1_decoder;
extern const FFCodec ff_vc1_crystalhd_decoder;
extern const FFCodec ff_vc1image_decoder;
extern const FFCodec ff_vc1_mmal_decoder;
extern const FFCodec ff_vc1_qsv_decoder;
extern const FFCodec ff_vc1_v4l2m2m_decoder;
extern const FFCodec ff_vc2_encoder;
extern const FFCodec ff_vcr1_decoder;
extern const FFCodec ff_vmdvideo_decoder;
extern const FFCodec ff_vmnc_decoder;
extern const FFCodec ff_vp3_decoder;
extern const FFCodec ff_vp4_decoder;
extern const FFCodec ff_vp5_decoder;
extern const FFCodec ff_vp6_decoder;
extern const FFCodec ff_vp6a_decoder;
extern const FFCodec ff_vp6f_decoder;
extern const FFCodec ff_vp7_decoder;
extern const FFCodec ff_vp8_decoder;
extern const FFCodec ff_vp8_rkmpp_decoder;
extern const FFCodec ff_vp8_v4l2m2m_decoder;
extern const FFCodec ff_vp9_decoder;
extern const FFCodec ff_vp9_rkmpp_decoder;
extern const FFCodec ff_vp9_v4l2m2m_decoder;
extern const FFCodec ff_vqa_decoder;
extern const FFCodec ff_vqc_decoder;
extern const FFCodec ff_wbmp_decoder;
extern const FFCodec ff_wbmp_encoder;
extern const FFCodec ff_webp_decoder;
extern const FFCodec ff_wcmv_decoder;
extern const FFCodec ff_wrapped_avframe_encoder;
extern const FFCodec ff_wrapped_avframe_decoder;
extern const FFCodec ff_wmv1_encoder;
extern const FFCodec ff_wmv1_decoder;
extern const FFCodec ff_wmv2_encoder;
extern const FFCodec ff_wmv2_decoder;
extern const FFCodec ff_wmv3_decoder;
extern const FFCodec ff_wmv3_crystalhd_decoder;
extern const FFCodec ff_wmv3image_decoder;
extern const FFCodec ff_wnv1_decoder;
extern const FFCodec ff_xan_wc3_decoder;
extern const FFCodec ff_xan_wc4_decoder;
extern const FFCodec ff_xbm_encoder;
extern const FFCodec ff_xbm_decoder;
extern const FFCodec ff_xface_encoder;
extern const FFCodec ff_xface_decoder;
extern const FFCodec ff_xl_decoder;
extern const FFCodec ff_xpm_decoder;
extern const FFCodec ff_xwd_encoder;
extern const FFCodec ff_xwd_decoder;
extern const FFCodec ff_y41p_encoder;
extern const FFCodec ff_y41p_decoder;
extern const FFCodec ff_ylc_decoder;
extern const FFCodec ff_yop_decoder;
extern const FFCodec ff_yuv4_encoder;
extern const FFCodec ff_yuv4_decoder;
extern const FFCodec ff_zero12v_decoder;
extern const FFCodec ff_zerocodec_decoder;
extern const FFCodec ff_zlib_encoder;
extern const FFCodec ff_zlib_decoder;
extern const FFCodec ff_zmbv_encoder;
extern const FFCodec ff_zmbv_decoder;

/* audio codecs */
extern const FFCodec ff_aac_encoder;
extern const FFCodec ff_aac_decoder;
extern const FFCodec ff_aac_fixed_decoder;
extern const FFCodec ff_aac_latm_decoder;
extern const FFCodec ff_ac3_encoder;
extern const FFCodec ff_ac3_decoder;
extern const FFCodec ff_ac3_fixed_encoder;
extern const FFCodec ff_ac3_fixed_decoder;
extern const FFCodec ff_acelp_kelvin_decoder;
extern const FFCodec ff_alac_encoder;
extern const FFCodec ff_alac_decoder;
extern const FFCodec ff_als_decoder;
extern const FFCodec ff_amrnb_decoder;
extern const FFCodec ff_amrwb_decoder;
extern const FFCodec ff_apac_decoder;
extern const FFCodec ff_ape_decoder;
extern const FFCodec ff_aptx_encoder;
extern const FFCodec ff_aptx_decoder;
extern const FFCodec ff_aptx_hd_encoder;
extern const FFCodec ff_aptx_hd_decoder;
extern const FFCodec ff_atrac1_decoder;
extern const FFCodec ff_atrac3_decoder;
extern const FFCodec ff_atrac3al_decoder;
extern const FFCodec ff_atrac3p_decoder;
extern const FFCodec ff_atrac3pal_decoder;
extern const FFCodec ff_atrac9_decoder;
extern const FFCodec ff_binkaudio_dct_decoder;
extern const FFCodec ff_binkaudio_rdft_decoder;
extern const FFCodec ff_bmv_audio_decoder;
extern const FFCodec ff_bonk_decoder;
extern const FFCodec ff_cook_decoder;
extern const FFCodec ff_dca_encoder;
extern const FFCodec ff_dca_decoder;
extern const FFCodec ff_dfpwm_encoder;
extern const FFCodec ff_dfpwm_decoder;
extern const FFCodec ff_dolby_e_decoder;
extern const FFCodec ff_dsd_lsbf_decoder;
extern const FFCodec ff_dsd_msbf_decoder;
extern const FFCodec ff_dsd_lsbf_planar_decoder;
extern const FFCodec ff_dsd_msbf_planar_decoder;
extern const FFCodec ff_dsicinaudio_decoder;
extern const FFCodec ff_dss_sp_decoder;
extern const FFCodec ff_dst_decoder;
extern const FFCodec ff_eac3_encoder;
extern const FFCodec ff_eac3_decoder;
extern const FFCodec ff_evrc_decoder;
extern const FFCodec ff_fastaudio_decoder;
extern const FFCodec ff_ffwavesynth_decoder;
extern const FFCodec ff_flac_encoder;
extern const FFCodec ff_flac_decoder;
extern const FFCodec ff_ftr_decoder;
extern const FFCodec ff_g723_1_encoder;
extern const FFCodec ff_g723_1_decoder;
extern const FFCodec ff_g729_decoder;
extern const FFCodec ff_gsm_decoder;
extern const FFCodec ff_gsm_ms_decoder;
extern const FFCodec ff_hca_decoder;
extern const FFCodec ff_hcom_decoder;
extern const FFCodec ff_hdr_encoder;
extern const FFCodec ff_hdr_decoder;
extern const FFCodec ff_iac_decoder;
extern const FFCodec ff_ilbc_decoder;
extern const FFCodec ff_imc_decoder;
extern const FFCodec ff_interplay_acm_decoder;
extern const FFCodec ff_mace3_decoder;
extern const FFCodec ff_mace6_decoder;
extern const FFCodec ff_metasound_decoder;
extern const FFCodec ff_misc4_decoder;
extern const FFCodec ff_mlp_encoder;
extern const FFCodec ff_mlp_decoder;
extern const FFCodec ff_mp1_decoder;
extern const FFCodec ff_mp1float_decoder;
extern const FFCodec ff_mp2_encoder;
extern const FFCodec ff_mp2_decoder;
extern const FFCodec ff_mp2float_decoder;
extern const FFCodec ff_mp2fixed_encoder;
extern const FFCodec ff_mp3float_decoder;
extern const FFCodec ff_mp3_decoder;
extern const FFCodec ff_mp3adufloat_decoder;
extern const FFCodec ff_mp3adu_decoder;
extern const FFCodec ff_mp3on4float_decoder;
extern const FFCodec ff_mp3on4_decoder;
extern const FFCodec ff_mpc7_decoder;
extern const FFCodec ff_mpc8_decoder;
extern const FFCodec ff_msnsiren_decoder;
extern const FFCodec ff_nellymoser_encoder;
extern const FFCodec ff_nellymoser_decoder;
extern const FFCodec ff_on2avc_decoder;
extern const FFCodec ff_opus_encoder;
extern const FFCodec ff_opus_decoder;
extern const FFCodec ff_paf_audio_decoder;
extern const FFCodec ff_qcelp_decoder;
extern const FFCodec ff_qdm2_decoder;
extern const FFCodec ff_qdmc_decoder;
extern const FFCodec ff_ra_144_encoder;
extern const FFCodec ff_ra_144_decoder;
extern const FFCodec ff_ra_288_decoder;
extern const FFCodec ff_ralf_decoder;
extern const FFCodec ff_sbc_encoder;
extern const FFCodec ff_sbc_decoder;
extern const FFCodec ff_shorten_decoder;
extern const FFCodec ff_sipr_decoder;
extern const FFCodec ff_siren_decoder;
extern const FFCodec ff_smackaud_decoder;
extern const FFCodec ff_sonic_encoder;
extern const FFCodec ff_sonic_decoder;
extern const FFCodec ff_sonic_ls_encoder;
extern const FFCodec ff_tak_decoder;
extern const FFCodec ff_truehd_encoder;
extern const FFCodec ff_truehd_decoder;
extern const FFCodec ff_truespeech_decoder;
extern const FFCodec ff_tta_encoder;
extern const FFCodec ff_tta_decoder;
extern const FFCodec ff_twinvq_decoder;
extern const FFCodec ff_vmdaudio_decoder;
extern const FFCodec ff_vorbis_encoder;
extern const FFCodec ff_vorbis_decoder;
extern const FFCodec ff_wavarc_decoder;
extern const FFCodec ff_wavpack_encoder;
extern const FFCodec ff_wavpack_decoder;
extern const FFCodec ff_wmalossless_decoder;
extern const FFCodec ff_wmapro_decoder;
extern const FFCodec ff_wmav1_encoder;
extern const FFCodec ff_wmav1_decoder;
extern const FFCodec ff_wmav2_encoder;
extern const FFCodec ff_wmav2_decoder;
extern const FFCodec ff_wmavoice_decoder;
extern const FFCodec ff_ws_snd1_decoder;
extern const FFCodec ff_xma1_decoder;
extern const FFCodec ff_xma2_decoder;

/* PCM codecs */
extern const FFCodec ff_pcm_alaw_encoder;
extern const FFCodec ff_pcm_alaw_decoder;
extern const FFCodec ff_pcm_bluray_encoder;
extern const FFCodec ff_pcm_bluray_decoder;
extern const FFCodec ff_pcm_dvd_encoder;
extern const FFCodec ff_pcm_dvd_decoder;
extern const FFCodec ff_pcm_f16le_decoder;
extern const FFCodec ff_pcm_f24le_decoder;
extern const FFCodec ff_pcm_f32be_encoder;
extern const FFCodec ff_pcm_f32be_decoder;
extern const FFCodec ff_pcm_f32le_encoder;
extern const FFCodec ff_pcm_f32le_decoder;
extern const FFCodec ff_pcm_f64be_encoder;
extern const FFCodec ff_pcm_f64be_decoder;
extern const FFCodec ff_pcm_f64le_encoder;
extern const FFCodec ff_pcm_f64le_decoder;
extern const FFCodec ff_pcm_lxf_decoder;
extern const FFCodec ff_pcm_mulaw_encoder;
extern const FFCodec ff_pcm_mulaw_decoder;
extern const FFCodec ff_pcm_s8_encoder;
extern const FFCodec ff_pcm_s8_decoder;
extern const FFCodec ff_pcm_s8_planar_encoder;
extern const FFCodec ff_pcm_s8_planar_decoder;
extern const FFCodec ff_pcm_s16be_encoder;
extern const FFCodec ff_pcm_s16be_decoder;
extern const FFCodec ff_pcm_s16be_planar_encoder;
extern const FFCodec ff_pcm_s16be_planar_decoder;
extern const FFCodec ff_pcm_s16le_encoder;
extern const FFCodec ff_pcm_s16le_decoder;
extern const FFCodec ff_pcm_s16le_planar_encoder;
extern const FFCodec ff_pcm_s16le_planar_decoder;
extern const FFCodec ff_pcm_s24be_encoder;
extern const FFCodec ff_pcm_s24be_decoder;
extern const FFCodec ff_pcm_s24daud_encoder;
extern const FFCodec ff_pcm_s24daud_decoder;
extern const FFCodec ff_pcm_s24le_encoder;
extern const FFCodec ff_pcm_s24le_decoder;
extern const FFCodec ff_pcm_s24le_planar_encoder;
extern const FFCodec ff_pcm_s24le_planar_decoder;
extern const FFCodec ff_pcm_s32be_encoder;
extern const FFCodec ff_pcm_s32be_decoder;
extern const FFCodec ff_pcm_s32le_encoder;
extern const FFCodec ff_pcm_s32le_decoder;
extern const FFCodec ff_pcm_s32le_planar_encoder;
extern const FFCodec ff_pcm_s32le_planar_decoder;
extern const FFCodec ff_pcm_s64be_encoder;
extern const FFCodec ff_pcm_s64be_decoder;
extern const FFCodec ff_pcm_s64le_encoder;
extern const FFCodec ff_pcm_s64le_decoder;
extern const FFCodec ff_pcm_sga_decoder;
extern const FFCodec ff_pcm_u8_encoder;
extern const FFCodec ff_pcm_u8_decoder;
extern const FFCodec ff_pcm_u16be_encoder;
extern const FFCodec ff_pcm_u16be_decoder;
extern const FFCodec ff_pcm_u16le_encoder;
extern const FFCodec ff_pcm_u16le_decoder;
extern const FFCodec ff_pcm_u24be_encoder;
extern const FFCodec ff_pcm_u24be_decoder;
extern const FFCodec ff_pcm_u24le_encoder;
extern const FFCodec ff_pcm_u24le_decoder;
extern const FFCodec ff_pcm_u32be_encoder;
extern const FFCodec ff_pcm_u32be_decoder;
extern const FFCodec ff_pcm_u32le_encoder;
extern const FFCodec ff_pcm_u32le_decoder;
extern const FFCodec ff_pcm_vidc_encoder;
extern const FFCodec ff_pcm_vidc_decoder;

/* DPCM codecs */
extern const FFCodec ff_cbd2_dpcm_decoder;
extern const FFCodec ff_derf_dpcm_decoder;
extern const FFCodec ff_gremlin_dpcm_decoder;
extern const FFCodec ff_interplay_dpcm_decoder;
extern const FFCodec ff_roq_dpcm_encoder;
extern const FFCodec ff_roq_dpcm_decoder;
extern const FFCodec ff_sdx2_dpcm_decoder;
extern const FFCodec ff_sol_dpcm_decoder;
extern const FFCodec ff_xan_dpcm_decoder;
extern const FFCodec ff_wady_dpcm_decoder;

/* ADPCM codecs */
extern const FFCodec ff_adpcm_4xm_decoder;
extern const FFCodec ff_adpcm_adx_encoder;
extern const FFCodec ff_adpcm_adx_decoder;
extern const FFCodec ff_adpcm_afc_decoder;
extern const FFCodec ff_adpcm_agm_decoder;
extern const FFCodec ff_adpcm_aica_decoder;
extern const FFCodec ff_adpcm_argo_decoder;
extern const FFCodec ff_adpcm_argo_encoder;
extern const FFCodec ff_adpcm_ct_decoder;
extern const FFCodec ff_adpcm_dtk_decoder;
extern const FFCodec ff_adpcm_ea_decoder;
extern const FFCodec ff_adpcm_ea_maxis_xa_decoder;
extern const FFCodec ff_adpcm_ea_r1_decoder;
extern const FFCodec ff_adpcm_ea_r2_decoder;
extern const FFCodec ff_adpcm_ea_r3_decoder;
extern const FFCodec ff_adpcm_ea_xas_decoder;
extern const FFCodec ff_adpcm_g722_encoder;
extern const FFCodec ff_adpcm_g722_decoder;
extern const FFCodec ff_adpcm_g726_encoder;
extern const FFCodec ff_adpcm_g726_decoder;
extern const FFCodec ff_adpcm_g726le_encoder;
extern const FFCodec ff_adpcm_g726le_decoder;
extern const FFCodec ff_adpcm_ima_acorn_decoder;
extern const FFCodec ff_adpcm_ima_amv_decoder;
extern const FFCodec ff_adpcm_ima_amv_encoder;
extern const FFCodec ff_adpcm_ima_alp_decoder;
extern const FFCodec ff_adpcm_ima_alp_encoder;
extern const FFCodec ff_adpcm_ima_apc_decoder;
extern const FFCodec ff_adpcm_ima_apm_decoder;
extern const FFCodec ff_adpcm_ima_apm_encoder;
extern const FFCodec ff_adpcm_ima_cunning_decoder;
extern const FFCodec ff_adpcm_ima_dat4_decoder;
extern const FFCodec ff_adpcm_ima_dk3_decoder;
extern const FFCodec ff_adpcm_ima_dk4_decoder;
extern const FFCodec ff_adpcm_ima_ea_eacs_decoder;
extern const FFCodec ff_adpcm_ima_ea_sead_decoder;
extern const FFCodec ff_adpcm_ima_iss_decoder;
extern const FFCodec ff_adpcm_ima_moflex_decoder;
extern const FFCodec ff_adpcm_ima_mtf_decoder;
extern const FFCodec ff_adpcm_ima_oki_decoder;
extern const FFCodec ff_adpcm_ima_qt_encoder;
extern const FFCodec ff_adpcm_ima_qt_decoder;
extern const FFCodec ff_adpcm_ima_rad_decoder;
extern const FFCodec ff_adpcm_ima_ssi_decoder;
extern const FFCodec ff_adpcm_ima_ssi_encoder;
extern const FFCodec ff_adpcm_ima_smjpeg_decoder;
extern const FFCodec ff_adpcm_ima_wav_encoder;
extern const FFCodec ff_adpcm_ima_wav_decoder;
extern const FFCodec ff_adpcm_ima_ws_encoder;
extern const FFCodec ff_adpcm_ima_ws_decoder;
extern const FFCodec ff_adpcm_ms_encoder;
extern const FFCodec ff_adpcm_ms_decoder;
extern const FFCodec ff_adpcm_mtaf_decoder;
extern const FFCodec ff_adpcm_psx_decoder;
extern const FFCodec ff_adpcm_sbpro_2_decoder;
extern const FFCodec ff_adpcm_sbpro_3_decoder;
extern const FFCodec ff_adpcm_sbpro_4_decoder;
extern const FFCodec ff_adpcm_swf_encoder;
extern const FFCodec ff_adpcm_swf_decoder;
extern const FFCodec ff_adpcm_thp_decoder;
extern const FFCodec ff_adpcm_thp_le_decoder;
extern const FFCodec ff_adpcm_vima_decoder;
extern const FFCodec ff_adpcm_xa_decoder;
extern const FFCodec ff_adpcm_xmd_decoder;
extern const FFCodec ff_adpcm_yamaha_encoder;
extern const FFCodec ff_adpcm_yamaha_decoder;
extern const FFCodec ff_adpcm_zork_decoder;

/* subtitles */
extern const FFCodec ff_ssa_encoder;
extern const FFCodec ff_ssa_decoder;
extern const FFCodec ff_ass_encoder;
extern const FFCodec ff_ass_decoder;
extern const FFCodec ff_ccaption_decoder;
extern const FFCodec ff_dvbsub_encoder;
extern const FFCodec ff_dvbsub_decoder;
extern const FFCodec ff_dvdsub_encoder;
extern const FFCodec ff_dvdsub_decoder;
extern const FFCodec ff_jacosub_decoder;
extern const FFCodec ff_microdvd_decoder;
extern const FFCodec ff_movtext_encoder;
extern const FFCodec ff_movtext_decoder;
extern const FFCodec ff_mpl2_decoder;
extern const FFCodec ff_pgssub_decoder;
extern const FFCodec ff_pjs_decoder;
extern const FFCodec ff_realtext_decoder;
extern const FFCodec ff_sami_decoder;
extern const FFCodec ff_srt_encoder;
extern const FFCodec ff_srt_decoder;
extern const FFCodec ff_stl_decoder;
extern const FFCodec ff_subrip_encoder;
extern const FFCodec ff_subrip_decoder;
extern const FFCodec ff_subviewer_decoder;
extern const FFCodec ff_subviewer1_decoder;
extern const FFCodec ff_text_encoder;
extern const FFCodec ff_text_decoder;
extern const FFCodec ff_ttml_encoder;
extern const FFCodec ff_vplayer_decoder;
extern const FFCodec ff_webvtt_encoder;
extern const FFCodec ff_webvtt_decoder;
extern const FFCodec ff_xsub_encoder;
extern const FFCodec ff_xsub_decoder;

/* external libraries */
extern const FFCodec ff_aac_at_encoder;
extern const FFCodec ff_aac_at_decoder;
extern const FFCodec ff_ac3_at_decoder;
extern const FFCodec ff_adpcm_ima_qt_at_decoder;
extern const FFCodec ff_alac_at_encoder;
extern const FFCodec ff_alac_at_decoder;
extern const FFCodec ff_amr_nb_at_decoder;
extern const FFCodec ff_eac3_at_decoder;
extern const FFCodec ff_gsm_ms_at_decoder;
extern const FFCodec ff_ilbc_at_encoder;
extern const FFCodec ff_ilbc_at_decoder;
extern const FFCodec ff_mp1_at_decoder;
extern const FFCodec ff_mp2_at_decoder;
extern const FFCodec ff_mp3_at_decoder;
extern const FFCodec ff_pcm_alaw_at_encoder;
extern const FFCodec ff_pcm_alaw_at_decoder;
extern const FFCodec ff_pcm_mulaw_at_encoder;
extern const FFCodec ff_pcm_mulaw_at_decoder;
extern const FFCodec ff_qdmc_at_decoder;
extern const FFCodec ff_qdm2_at_decoder;
extern FFCodec ff_libaom_av1_encoder;
extern const FFCodec ff_libaribb24_decoder;
extern const FFCodec ff_libcelt_decoder;
extern const FFCodec ff_libcodec2_encoder;
extern const FFCodec ff_libcodec2_decoder;
extern const FFCodec ff_libdav1d_decoder;
extern const FFCodec ff_libdavs2_decoder;
extern const FFCodec ff_libfdk_aac_encoder;
extern const FFCodec ff_libfdk_aac_decoder;
extern const FFCodec ff_libgsm_encoder;
extern const FFCodec ff_libgsm_decoder;
extern const FFCodec ff_libgsm_ms_encoder;
extern const FFCodec ff_libgsm_ms_decoder;
extern const FFCodec ff_libilbc_encoder;
extern const FFCodec ff_libilbc_decoder;
extern const FFCodec ff_libjxl_decoder;
extern const FFCodec ff_libjxl_encoder;
extern const FFCodec ff_libmp3lame_encoder;
extern const FFCodec ff_libopencore_amrnb_encoder;
extern const FFCodec ff_libopencore_amrnb_decoder;
extern const FFCodec ff_libopencore_amrwb_decoder;
extern const FFCodec ff_libopenjpeg_encoder;
extern const FFCodec ff_libopenjpeg_decoder;
extern const FFCodec ff_libopus_encoder;
extern const FFCodec ff_libopus_decoder;
extern const FFCodec ff_librav1e_encoder;
extern const FFCodec ff_librsvg_decoder;
extern const FFCodec ff_libshine_encoder;
extern const FFCodec ff_libspeex_encoder;
extern const FFCodec ff_libspeex_decoder;
extern const FFCodec ff_libsvtav1_encoder;
extern const FFCodec ff_libtheora_encoder;
extern const FFCodec ff_libtwolame_encoder;
extern const FFCodec ff_libuavs3d_decoder;
extern const FFCodec ff_libvo_amrwbenc_encoder;
extern const FFCodec ff_libvorbis_encoder;
extern const FFCodec ff_libvorbis_decoder;
extern const FFCodec ff_libvpx_vp8_encoder;
extern const FFCodec ff_libvpx_vp8_decoder;
extern FFCodec ff_libvpx_vp9_encoder;
extern FFCodec ff_libvpx_vp9_decoder;
/* preferred over libwebp */
extern const FFCodec ff_libwebp_anim_encoder;
extern const FFCodec ff_libwebp_encoder;
extern const FFCodec ff_libx262_encoder;
#if CONFIG_LIBX264_ENCODER
#include <x264.h>
#if X264_BUILD < 153
#define LIBX264_CONST
#else
#define LIBX264_CONST const
#endif
extern LIBX264_CONST FFCodec ff_libx264_encoder;
#endif
extern const FFCodec ff_libx264rgb_encoder;
extern FFCodec ff_libx265_encoder;
extern const FFCodec ff_libxavs_encoder;
extern const FFCodec ff_libxavs2_encoder;
extern const FFCodec ff_libxvid_encoder;
extern const FFCodec ff_libzvbi_teletext_decoder;

/* text */
extern const FFCodec ff_bintext_decoder;
extern const FFCodec ff_xbin_decoder;
extern const FFCodec ff_idf_decoder;

/* external libraries, that shouldn't be used by default if one of the
 * above is available */
extern const FFCodec ff_aac_mf_encoder;
extern const FFCodec ff_ac3_mf_encoder;
extern const FFCodec ff_h263_v4l2m2m_encoder;
extern const FFCodec ff_libaom_av1_decoder;
/* hwaccel hooks only, so prefer external decoders */
extern const FFCodec ff_av1_decoder;
extern const FFCodec ff_av1_cuvid_decoder;
extern const FFCodec ff_av1_mediacodec_decoder;
extern const FFCodec ff_av1_nvenc_encoder;
extern const FFCodec ff_av1_qsv_decoder;
extern const FFCodec ff_av1_qsv_encoder;
extern const FFCodec ff_av1_amf_encoder;
extern const FFCodec ff_libopenh264_encoder;
extern const FFCodec ff_libopenh264_decoder;
extern const FFCodec ff_h264_amf_encoder;
extern const FFCodec ff_h264_cuvid_decoder;
extern const FFCodec ff_h264_mf_encoder;
extern const FFCodec ff_h264_nvenc_encoder;
extern const FFCodec ff_h264_omx_encoder;
extern const FFCodec ff_h264_qsv_encoder;
extern const FFCodec ff_h264_v4l2m2m_encoder;
extern const FFCodec ff_h264_vaapi_encoder;
extern const FFCodec ff_h264_videotoolbox_encoder;
extern const FFCodec ff_hevc_amf_encoder;
extern const FFCodec ff_hevc_cuvid_decoder;
extern const FFCodec ff_hevc_mediacodec_decoder;
extern const FFCodec ff_hevc_mediacodec_encoder;
extern const FFCodec ff_hevc_mf_encoder;
extern const FFCodec ff_hevc_nvenc_encoder;
extern const FFCodec ff_hevc_qsv_encoder;
extern const FFCodec ff_hevc_v4l2m2m_encoder;
extern const FFCodec ff_hevc_vaapi_encoder;
extern const FFCodec ff_hevc_videotoolbox_encoder;
extern const FFCodec ff_libkvazaar_encoder;
extern const FFCodec ff_mjpeg_cuvid_decoder;
extern const FFCodec ff_mjpeg_qsv_encoder;
extern const FFCodec ff_mjpeg_qsv_decoder;
extern const FFCodec ff_mjpeg_vaapi_encoder;
extern const FFCodec ff_mp3_mf_encoder;
extern const FFCodec ff_mpeg1_cuvid_decoder;
extern const FFCodec ff_mpeg2_cuvid_decoder;
extern const FFCodec ff_mpeg2_qsv_encoder;
extern const FFCodec ff_mpeg2_vaapi_encoder;
extern const FFCodec ff_mpeg4_cuvid_decoder;
extern const FFCodec ff_mpeg4_mediacodec_decoder;
extern const FFCodec ff_mpeg4_omx_encoder;
extern const FFCodec ff_mpeg4_v4l2m2m_encoder;
extern const FFCodec ff_prores_videotoolbox_encoder;
extern const FFCodec ff_vc1_cuvid_decoder;
extern const FFCodec ff_vp8_cuvid_decoder;
extern const FFCodec ff_vp8_mediacodec_decoder;
extern const FFCodec ff_vp8_qsv_decoder;
extern const FFCodec ff_vp8_v4l2m2m_encoder;
extern const FFCodec ff_vp8_vaapi_encoder;
extern const FFCodec ff_vp9_cuvid_decoder;
extern const FFCodec ff_vp9_mediacodec_decoder;
extern const FFCodec ff_vp9_qsv_decoder;
extern const FFCodec ff_vp9_vaapi_encoder;
extern const FFCodec ff_vp9_qsv_encoder;

// null codecs
extern const FFCodec ff_vnull_decoder;
extern const FFCodec ff_vnull_encoder;
extern const FFCodec ff_anull_decoder;
extern const FFCodec ff_anull_encoder;

// The iterate API is not usable with ossfuzz due to the excessive size of binaries created
#if CONFIG_OSSFUZZ
const FFCodec * codec_list[] = {
    NULL,
    NULL,
    NULL
};
#else
#include "libavcodec/codec_list.c"
#endif

static AVOnce av_codec_static_init = AV_ONCE_INIT;
static void av_codec_init_static(void)
{
    for (int i = 0; codec_list[i]; i++) {
        if (codec_list[i]->init_static_data)
            codec_list[i]->init_static_data((FFCodec*)codec_list[i]);
    }
}

const AVCodec *av_codec_iterate(void **opaque)
{
    uintptr_t i = (uintptr_t)*opaque;
    const FFCodec *c = codec_list[i];

    ff_thread_once(&av_codec_static_init, av_codec_init_static);

    if (c) {
        *opaque = (void*)(i + 1);
        return &c->p;
    }
    return NULL;
}

static enum AVCodecID remap_deprecated_codec_id(enum AVCodecID id)
{
    switch(id){
        //This is for future deprecatec codec ids, its empty since
        //last major bump but will fill up again over time, please don't remove it
        default                                         : return id;
    }
}

static const AVCodec *find_codec(enum AVCodecID id, int (*x)(const AVCodec *))
{
    const AVCodec *p, *experimental = NULL;
    void *i = 0;

    id = remap_deprecated_codec_id(id);

    while ((p = av_codec_iterate(&i))) {
        if (!x(p))
            continue;
        if (p->id == id) {
            if (p->capabilities & AV_CODEC_CAP_EXPERIMENTAL && !experimental) {
                experimental = p;
            } else
                return p;
        }
    }

    return experimental;
}

const AVCodec *avcodec_find_encoder(enum AVCodecID id)
{
    return find_codec(id, av_codec_is_encoder);
}

const AVCodec *avcodec_find_decoder(enum AVCodecID id)
{
    return find_codec(id, av_codec_is_decoder);
}

static const AVCodec *find_codec_by_name(const char *name, int (*x)(const AVCodec *))
{
    void *i = 0;
    const AVCodec *p;

    if (!name)
        return NULL;

    while ((p = av_codec_iterate(&i))) {
        if (!x(p))
            continue;
        if (strcmp(name, p->name) == 0)
            return p;
    }

    return NULL;
}

const AVCodec *avcodec_find_encoder_by_name(const char *name)
{
    return find_codec_by_name(name, av_codec_is_encoder);
}

const AVCodec *avcodec_find_decoder_by_name(const char *name)
{
    return find_codec_by_name(name, av_codec_is_decoder);
}

2.通过编码器得到编码器上下文

 AVCodecContext *avcodec_alloc_context3(const AVCodec *codec);

/**
 * Allocate an AVCodecContext and set its fields to default values. The
 * resulting struct should be freed with avcodec_free_context().
 *
 * @param codec if non-NULL, allocate private data and initialize defaults
 *              for the given codec. It is illegal to then call avcodec_open2()
 *              with a different codec.
 *              If NULL, then the codec-specific defaults won't be initialized,
 *              which may result in suboptimal default settings (this is
 *              important mainly for encoders, e.g. libx264).
 *
 * @return An AVCodecContext filled with default values or NULL on failure.
 */
AVCodecContext *avcodec_alloc_context3(const AVCodec *codec);

3.通过编码器上下文 打开编码器

int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);

参数：

AVCodecContext *avctx：传递的编码器上下文

const AVCodec *codec：如果我们在 创建编码器的时候，传递的是nullptr，那么这时候就要传递具体的codec

AVDictionary **options：一个包含AVCodecContext和编解码器私有选项的字典。返回时，此对象将填充未找到的选项。（这个红色部分的翻译很二，完全看不懂啥意思，），

重新翻译：（可选）一个包含编解码器特定选项的字符串。 这是一个以key=value形式的选项列表，用,分隔。如果不需要额外的选项，可以直接传递NULL。关于 AVDictionary，很显然，这个AVDictionary是为了AVCodecContext 用的，也就是我们指定的编码器（例如h264）有一些参数需要设置，可以通过AVDictionary设置。

我们有两个疑问在这里：

注意的是通过AVDictionary设置的是 特定编码器特定的参数，如果是通用的参数，avcodec中是有key的，通过avcodec设置就好。

1.怎么知道特定的编码器有哪些参数要设置（例如h264编码器有哪些特殊的参数）

        从这里看出，如果要设置这些参数，首先要明白h264的原理，文件结构，因此这里也很有必要学习x264。 另外这里可以参考如何知道x264的参数，了解x265的参数。

2.如何使用 AVDictionary 设定这些特定的参数

核心就是 使用 av_dict_set 一系列方法。        

这里注意的是：如果有特定的参数，设定到AVDictionary后，才能使用 open。

3.还有一种方法是通过 av_opt_set 设定这些特殊的参数

核心是使用 av_opt_set 一系列方法。

例如 

    /// 恒定速率因子（CRF）
    av_opt_set_int(c->priv_data, "crf", 23, 0);

/**
 * Initialize the AVCodecContext to use the given AVCodec. Prior to using this
 * function the context has to be allocated with avcodec_alloc_context3().
 *
 * The functions avcodec_find_decoder_by_name(), avcodec_find_encoder_by_name(),
 * avcodec_find_decoder() and avcodec_find_encoder() provide an easy way for
 * retrieving a codec.
 *
 * @note Always call this function before using decoding routines (such as
 * @ref avcodec_receive_frame()).
 *
 * @code
 * av_dict_set(&opts, "b", "2.5M", 0);
 * codec = avcodec_find_decoder(AV_CODEC_ID_H264);
 * if (!codec)
 *     exit(1);
 *
 * context = avcodec_alloc_context3(codec);
 *
 * if (avcodec_open2(context, codec, opts) < 0)
 *     exit(1);
 * @endcode
 *
 * @param avctx The context to initialize.
 * @param codec The codec to open this context for. If a non-NULL codec has been
 *              previously passed to avcodec_alloc_context3() or
 *              for this context, then this parameter MUST be either NULL or
 *              equal to the previously passed codec.
 * @param options A dictionary filled with AVCodecContext and codec-private options.
 *                On return this object will be filled with options that were not found.
 *
 * @return zero on success, a negative value on error
 * @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(),
 *      av_dict_set(), av_opt_find().
 */
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);

4. 将avframe数据发送给 编码器上下文

int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

当然发送前，avframe里面是要有数据的。

/**
 * Supply a raw video or audio frame to the encoder. Use avcodec_receive_packet()
 * to retrieve buffered output packets.
 *
 * @param avctx     codec context
 * @param[in] frame AVFrame containing the raw audio or video frame to be encoded.
 *                  Ownership of the frame remains with the caller, and the
 *                  encoder will not write to the frame. The encoder may create
 *                  a reference to the frame data (or copy it if the frame is
 *                  not reference-counted).
 *                  It can be NULL, in which case it is considered a flush
 *                  packet.  This signals the end of the stream. If the encoder
 *                  still has packets buffered, it will return them after this
 *                  call. Once flushing mode has been entered, additional flush
 *                  packets are ignored, and sending frames will return
 *                  AVERROR_EOF.
 *
 *                  For audio:
 *                  If AV_CODEC_CAP_VARIABLE_FRAME_SIZE is set, then each frame
 *                  can have any number of samples.
 *                  If it is not set, frame->nb_samples must be equal to
 *                  avctx->frame_size for all frames except the last.
 *                  The final frame may be smaller than avctx->frame_size.
 * @retval 0                 success
 * @retval AVERROR(EAGAIN)   input is not accepted in the current state - user must
 *                           read output with avcodec_receive_packet() (once all
 *                           output is read, the packet should be resent, and the
 *                           call will not fail with EAGAIN).
 * @retval AVERROR_EOF       the encoder has been flushed, and no new frames can
 *                           be sent to it
 * @retval AVERROR(EINVAL)   codec not opened, it is a decoder, or requires flush
 * @retval AVERROR(ENOMEM)   failed to add packet to internal queue, or similar
 * @retval "another negative error code" legitimate encoding errors
 */
int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

5.从编码器上下文获得 avpacket

int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);

当然在avpacket 的时候，avpacket的空间是需要分配好的。

注意的是1：一帧avframe发送到 解码器上下文，有可能有好几帧avpacket 被解码器上下文 发送出来。

因此在 avcodec_send_frame 调用后，avcodec_receive_packet需要在一个循环中接受 解码器上下文发送出来的 avpacket。循环结束的条件是：avcodec_receive_packet的返回值，注意的是，这个返回值有好几种情况，要分开处理。

注意的是2：另外，循环结束后，还需要通过 avcodec_send_frame 的第二个参数为null，再刷新一下 编码器上下文的缓存。

注意的是3：在循环中，每次通过 avcodec_receive_packet 获得avpacket之后，还应该将avpacket通过 av_packet_unref 将avpacket的引用计数-1，防止内存泄漏。

/**
 * Read encoded data from the encoder.
 *
 * @param avctx codec context
 * @param avpkt This will be set to a reference-counted packet allocated by the
 *              encoder. Note that the function will always call
 *              av_packet_unref(avpkt) before doing anything else.
 * @retval 0               success
 * @retval AVERROR(EAGAIN) output is not available in the current state - user must
 *                         try to send input
 * @retval AVERROR_EOF     the encoder has been fully flushed, and there will be no
 *                         more output packets
 * @retval AVERROR(EINVAL) codec not opened, or it is a decoder
 * @retval "another negative error code" legitimate encoding errors
 */
int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);

6 代码

#include <iostream>
#include <fstream>
extern "C" {
	#include "libavcodec/avcodec.h"
	#include "libavcodec/codec.h"
}
using namespace std;

char* yuvfilename = (char *)"400_300_25.yuv";
char* h264filename = (char*)"400_300_25.h264";
ifstream fin;
ofstream fout;

AVCodecID codec_id_h264 = AV_CODEC_ID_H264;
AVCodecID codec_id_h265 = AV_CODEC_ID_H265;
AVCodecID codec_id_h265_1 = AV_CODEC_ID_HEVC;
AVCodec* avcodec = nullptr;
AVCodecContext* avcodecContext = nullptr;

AVFrame* avframe = nullptr;
AVPacket* avpacket = nullptr;
void freeAndClose();
/***
*
* 目的是从一个YUV文件中，读取YUV数据到AVFrame
* 然后通过 H264编码器将AVFrame 转换成AVPacket
* 将每一帧的AVPacket 直接写入 xxx.h264文件，编码后的数据有带startcode
* h264文件可以通过 VLC 播放器播放，
***/
int main1(int argc, char * argv[]) {
	cout << "014ChangeAVFrameToAVPakcet start" << endl;
	int ret = 0;

	//打开要读取的YUV 文件
	fin.open(yuvfilename, ios_base::binary);
	if (!fin) {
		ret = -1;
		cout << "open yuv file error yuvfilename = " << yuvfilename << endl;
		freeAndClose();
		return ret;
	}
	//打开要写入的h264文件
	fout.open(h264filename, ios_base::binary);
	if (!fout) {
		ret = -2;
		cout << "open h264 file error h264filename = " << h264filename << endl;
		freeAndClose();
		return ret;
	}

	//1.找到编码器
	avcodec = avcodec_find_encoder(codec_id_h264);
	if (avcodec == nullptr) {
		ret = -3;
		cout << "avcodec_find_encoder error codec_id_h264 = " << codec_id_h264 << endl;
		freeAndClose();
		return ret;
	}
	///2. 编码器上下文
	avcodecContext = avcodec_alloc_context3(avcodec);
	if (avcodecContext == nullptr) {
		ret = -3;
		cout << "avcodec_alloc_context3 error avcodec = " << avcodec->name << endl;
		freeAndClose();
		return ret;
	}
	///3. 设定编码器上下文的参数，例如视频的宽高，那么这个参数应该是我们要处理的视频的宽高
	//我们要处理的视频是 400_300_25.yuv
	///编码的时候，原始的视频是从 摄像头来的，那么也就是说，宽和高我们应该能知道
	avcodecContext->width = 400;
	avcodecContext->height = 300;
	avcodecContext->pix_fmt = AVPixelFormat::AV_PIX_FMT_YUV420P;
	avcodecContext->time_base = {1,25};
	avcodecContext->thread_count = 16; 


	//4.打开编码器上下文
	ret = avcodec_open2(avcodecContext, nullptr, nullptr);
	if (ret !=0 ) {
		ret = -4;
		cout << "avcodec_open2 error  avcodecContext= " << avcodecContext->codec->name << endl;
		freeAndClose();
		return ret;
	}


	//5.从 YUV 中读取数据到 AVFrame，那么首先要构建AVFrame，让YUV数据有地方放置
	avframe = av_frame_alloc();
	if (avframe == nullptr) {
		ret = -5;
		cout << "av_frame_alloc error  "  << endl;
		freeAndClose();
		return ret;
	}
	//5.1 构造 avframe的参数
	avframe->width = avcodecContext->width;
	avframe->height = avcodecContext->height;
	avframe->format = avcodecContext->pix_fmt;

	//手动的分配 avframe的linesize 和 data的空间大小 start
	//设置每一行 avframe的大小，还记得YUV420P，每一行的大小是多少吗
	//avframe->linesize[0] = { avcodecContext->width};
	//avframe->linesize[1] = { avcodecContext->width /2 };
	//avframe->linesize[2] = { avcodecContext->width /2 };
	//创造YUV存放数据的空间，一个avframe放置的就是一张图片的大小，YUV420P的存储是 Y存储在data[0]中，U存储在data[1]中，V存储在data[2]中
	// YUV420p的大小为 RGB888的一半，Y占1，U占1/4 ，V占1/4.
	avframe->data[3] = { 0 };
	avframe->data[0] = new unsigned char[avcodecContext->width * avcodecContext->height];
	avframe->data[1] = new unsigned char[avcodecContext->width * avcodecContext->height/4];
	avframe->data[2] = new unsigned char[avcodecContext->width * avcodecContext->height/4];
	//手动的分配 avframe的linesize 和 data的空间大小 end


	//获取avframe的空间
	ret= av_frame_get_buffer(avframe, 0);
	if (ret <0) {
		char errbuf[1024] = { 0 };
		av_strerror(ret, errbuf, sizeof(errbuf) - 1);
		freeAndClose();
		return ret;
	}

	//手动的分配 AVPacket
	avpacket = av_packet_alloc();
	if (avpacket == nullptr) {
		ret = -6;
		cout << "av_packet_alloc error  " << endl;
		freeAndClose();
		return ret;
	}
	//
	while (!fin.eof()) {
		if (!av_frame_is_writable(avframe)) {
			av_frame_make_writable(avframe);
		}
		fin.read((char*)avframe->data[0], avcodecContext->width * avcodecContext->height);
		fin.read((char*)avframe->data[1], avcodecContext->width * avcodecContext->height / 4);
		fin.read((char*)avframe->data[2], avcodecContext->width * avcodecContext->height / 4);
		//每次循环时候，理论上 avframe里面已经有了 一张图片的大小，那么下来就需要将这张图片发送给 avcodecContext
		//注意的是：发送一次avframe，可能收到多次的avpacket
		ret = avcodec_send_frame(avcodecContext, avframe);
		if (ret != 0) {
			//说明发送到 编码器的时候就有问题.那么就让继续读取下一帧，也可以直接退出。
			continue;
		}
		if (ret ==0) {
			//这说明 发送到编码器成功了,那么就要进入一个循环 中获取 avpacket
			while (true) {
				ret = avcodec_receive_packet(avcodecContext, avpacket);
				if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
					break;
				}
				if (ret < 0) {
					char buf[1024] = { 0 };
					av_strerror(ret, buf, sizeof(buf) - 1);
					cerr << "avcodec_receive_packet failed!" << buf << endl;
					break;
				}
				if (ret == 0) {
					//这时候 说明 编码器中的 avpacket是真的有数据的
					fout.write((char*)avpacket->data, avpacket->size);
					av_packet_unref(avpacket);
				}
			}
		}
	}

	//刷新
	ret = avcodec_send_frame(avcodecContext, nullptr);
	if (ret != 0) {
		//说明发送到 编码器的时候就有问题.说明没有啥能刷新的
		cout << "aaa" << endl;
	}
	int count = 0;
	while (ret == 0) {
		while (true) {
			ret = avcodec_receive_packet(avcodecContext, avpacket);
			if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
				break;
			}
			if (ret < 0) {
				char buf[1024] = { 0 };
				av_strerror(ret, buf, sizeof(buf) - 1);
				cerr << "avcodec_receive_packet failed!" << buf << endl;
				break;
			}
			if (ret == 0) {
				//这时候 说明 编码器中的 avpacket是真的有数据的
				count++;
				fout.write((char*)avpacket->data, avpacket->size);
				av_packet_unref(avpacket);
			}
		}
	}
	cout << "count = " << count << endl;
	freeAndClose();

	return ret;
}

void freeAndClose() {
	if (!avpacket) {
		av_packet_free(&avpacket);
	}
	if (avframe != nullptr) {
		int i = 0;
		while (!avframe->data[i]) {
			delete avframe->data[i];
			++i;
		}
	}
	if (avframe != nullptr) {
		av_frame_free(&avframe);
	}
	if (avcodecContext != nullptr) {
		avcodec_free_context(&avcodecContext);
	}
	if (!fout) {
		fout.close();
	}

	if (!fin) {
		fin.close();
	}

}

7.代码改动，int av_image_get_buffer_size(enum AVPixelFormat pix_fmt, int width, int height, int align); 根据ffmpeg的方法计算一张图片的大小。

前面的代码示例中，我们通过自己分配 avframe->data的空间大小做的，这样是OK的，但是有两个不优秀的地方，

第一是  我们分配的avframe的linesize大小，也是根据不同的 pixfmt要改动。YUV420分配的是：

    avframe->linesize[0] = { avcodecContext->width};
    avframe->linesize[1] = { avcodecContext->width /2 };
    avframe->linesize[2] = { avcodecContext->width /2 };

但是对于其他格式的原始数据，计算方式要改动，因此通用性不强。

第二是代码的通用性不好，YUV420P的图片的大小是    这么计算的

    avframe->data[3] = { 0 };
    avframe->data[0] = new unsigned char[avcodecContext->width * avcodecContext->height];
    avframe->data[1] = new unsigned char[avcodecContext->width * avcodecContext->height/4];
    avframe->data[2] = new unsigned char[avcodecContext->width * avcodecContext->height/4];

但是对于其他格式的原始数据，计算方式要改动，因此通用性不强。

像这样常用的填充 avframe的数据，ffmpeg 已经替我们提供了合适的方法。

根据传递的参数，得到一张图片的大小

 * @param pix_fmt  the pixel format of the image  图片的格式 AVPixelFormat
 * @param width    the width of the image in pixels   图片的宽度
 * @param height   the height of the image in pixels  图片的高度
 * @param align    the assumed linesize alignment   假定的linesize的对齐值: 如果传1，假设这张图片的格式是RGB888(一个像素的大小为 24位，也就是3个字节)，则这张图片的大小为  (宽 * 高 * 一个像素的大小)。如果是YUV420P，则是 宽 * 高 * 一个像素的大小（1.5个字节）。
 * @return the buffer size in bytes, a negative error code in case of failure

返回值为 根据 参数 计算出来的这张图片的大小。

/**
 * Return the size in bytes of the amount of data required to store an
 * image with the given parameters.
 *
 * @param pix_fmt  the pixel format of the image
 * @param width    the width of the image in pixels
 * @param height   the height of the image in pixels
 * @param align    the assumed linesize alignment
 * @return the buffer size in bytes, a negative error code in case of failure
 */
int av_image_get_buffer_size(enum AVPixelFormat pix_fmt, int width, int height, int align);

使用 

//先计算出一张图片的大小
int frame_bytes_bufsize = av_image_get_buffer_size(
            (enum AVPixelFormat)frame->format, 
            frame->width,
            frame->height, 
            1);

//我们在分配对应大小的空间
uint8_t* frame_bytes_buf = (uint8_t*)malloc(frame_bytes_bufsize);

//读取YUV文件/或者RGB 文件

for (;;) {
        memset(frame_bytes_buf, 0, frame_bytes_bufsize);
        size_t read_bytes = fread(frame_bytes_buf, 1, frame_bytes_bufsize, infile);
        int need_size = av_image_fill_arrays(frame->data, 
                    frame->linesize, 
                    frame_bytes_buf,
                    (enum AVPixelFormat)frame->format,
                    frame->width, 
                    frame->height, 
                    1);
        ///这时候数据已经在 avframe中了
        ///下来处理 avframe 数据
}

8.代码改动 int av_image_fill_arrays(

uint8_t *dst_data[4],

int dst_linesize[4], 

const uint8_t *src,

enum AVPixelFormat pix_fmt,

int width,

int height,

int align);

将第三个参数指针指向的数据，赋值给第一个参数。

那么怎么赋值呢？是根据4,5,6,7参数决定的，因此这里4,5,6,7参数 需要和 av_image_get_buffer_size方法的4个参数一样，不然赋值就有问题了。

这里要注意的是，avframe在这之前的linesize 是按照 通用的方式（一般在32位windows上是按照16位的对齐方式给出的），在这个方法使用后，会根据最后一个参数，重新改动 AVframe的 linesize

/**
 * Setup the data pointers and linesizes based on the specified image
 * parameters and the provided array.
 *
 * The fields of the given image are filled in by using the src
 * address which points to the image data buffer. Depending on the
 * specified pixel format, one or multiple image data pointers and
 * line sizes will be set.  If a planar format is specified, several
 * pointers will be set pointing to the different picture planes and
 * the line sizes of the different planes will be stored in the
 * lines_sizes array. Call with src == NULL to get the required
 * size for the src buffer.
 *
 * To allocate the buffer and fill in the dst_data and dst_linesize in
 * one call, use av_image_alloc().
 *
 * @param dst_data      data pointers to be filled in
 * @param dst_linesize  linesizes for the image in dst_data to be filled in
 * @param src           buffer which will contain or contains the actual image data, can be NULL
 * @param pix_fmt       the pixel format of the image
 * @param width         the width of the image in pixels
 * @param height        the height of the image in pixels
 * @param align         the value used in src for linesize alignment
 * @return the size in bytes required for src, a negative error code
 * in case of failure
 */
int av_image_fill_arrays(uint8_t *dst_data[4], int dst_linesize[4],
                         const uint8_t *src,
                         enum AVPixelFormat pix_fmt, int width, int height, int align);


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