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【音视频开发】变速与硬解码

article 2025/1/22 9:17:14

一、变速

作者在开发过程中需要进行对视频进行变速不变调的开发，于是使用sonic库来实现对应的功能。
sonic库github地址：https://github.com/waywardgeek/sonic

// 判断是否要变速
			if (is->useSonic)
			{
				is->useSonic = !is->useSonic;
				if (is->sonic_stream_ready)
				{
					sonicDestroyStream(is->sncStream);
				}
				is->sonic_stream_ready = true;
				is->sncStream = sonicCreateStream(is->audio_tgt.freq, is->audio_tgt.channels);
				sonicSetSpeed(is->sncStream, is->volume_speed);
				sonicSetPitch(is->sncStream, 1.0);
				sonicSetRate(is->sncStream, 1.0);	
			}
			// 进行了变速 
			if (is->volume_speed != 1.0 && is->audio_buf)
			{
				int actual_out_samples = is->audio_buf_size/ (is->audio_tgt.channels * av_get_bytes_per_sample(is->audio_tgt.fmt));
				int ret;
				int num_available_samples = 0;
				int out_size = 0;
				int sonic_samples = 0;

				ret = sonicWriteShortToStream(is->sncStream, (short*)is->audio_buf, actual_out_samples);
				num_available_samples = sonicSamplesAvailable(is->sncStream);
				out_size = num_available_samples * is->audio_tgt.channels * av_get_bytes_per_sample(is->audio_tgt.fmt);
				//printf("sonic_size:%d\n", out_size);

				av_fast_malloc(&is->sonic_buf, &is->sonic_buf_size, out_size);
				if (ret)
				{
					sonic_samples = sonicReadShortFromStream(is->sncStream, (short*)is->sonic_buf, num_available_samples);

					is->audio_buf = is->sonic_buf;
					is->audio_buf_size = sonic_samples * is->audio_tgt.channels * av_get_bytes_per_sample(is->audio_tgt.fmt);
					is->audio_buf_index = 0;
				}
			}

其中 sonicWriteShortToStream(is->sncStream, (short*)is->audio_buf, actual_out_samples);sonicWriteShortToStream函数需要传入short*参数因此对其大小要重新进行计算。

二、硬解码

本人使用ffmpegAPI来进行硬解码的初始化
const AVCodecHWConfig *avcodec_get_hw_config(const AVCodec *codec, int index);：根据视频的AVCode，以及影解码器的type（AVHWDeviceType）来获取对应的AVCodecHWConfig 。
int av_hwdevice_ctx_create(AVBufferRef ** device_ctx, enum AVHWDeviceType type,const char *device, AVDictionary *opts, int flags);：创建硬解码设备参数的上下文

int ret = av_hwdevice_ctx_create(&hw_device_buf, type, nullptr, nullptr,0);
			if (ret < 0) {
				fprintf(stderr, "Failed to create specified HW device.\n");
				return ret;
			}
			//AVCodecContext* avctx 解码器上下文进行绑定
			avctx->hw_device_ctx = av_buffer_ref(hw_device_buf); 
			avctx->get_format = get_hw_format;//绑定获取硬件解码format的回调函数返回参数为AVPixelFormat