FFmpeg —— 9.示例程序（三）：音视频分离（分离为PCM、YUV格式）

读取文件分离出音视频文件：音频格式为PCM码流，视频格式为YUV

程序源码

 

/*
 * 音视频解码：分离出音频文件和视频文件
 * 播放命令为：ffplay -ar 44100 -ac 1 -f s16le -i out.pcm
 * ffmpeg -y -i input.mp3 -acodec pcm_s16le -f s16le -ac 2 -ar 44100 16k.pcm
 */

#include 

extern "C"
{
#include "libavformat/avformat.h"
#include "libavdevice/avdevice.h"
#include "libavcodec/avcodec.h"
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"
#include "libavutil/imgutils.h"
}

/*
 * 音频播放命令：ffplay -ar 44100 -ac 1 -f s16le -i out.pcm
 */

int avcodec_save_audio_file(AVFormatContext *pFormatCtx, int streamIndex, char *fileName)
{
	AVCodec *pCodec;
	AVCodecContext *pCodecCtx;
	AVCodecParameters *codecpar = pFormatCtx->streams[streamIndex]->codecpar;

	//4.获取解码器（一）:音频
	//根据索引拿到对应的流
	pCodec = avcodec_find_decoder(codecpar->codec_id);
	if (!pCodec)
	{
		printf("can't decoder audio\n");
		return -1;
	}
	//申请一个解码上下文
	pCodecCtx = avcodec_alloc_context3(pCodec);
	if (!pCodecCtx)
	{
		printf("can't allocate a audio decoding context\n");
		return -1;
	}

	//用流解码信息初始化编码参数
	avcodec_parameters_to_context(pCodecCtx, codecpar);

	//没有此句会出现：Could not update timestamps for skipped samples
	pCodecCtx->pkt_timebase = pFormatCtx->streams[streamIndex]->time_base;

	//5.打开解码器
	if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
	{
		printf("can't open codec\n");
		return -1;
	}

//	printf("--------------- File Information ----------------\n");
//	av_dump_format(pFormatCtx, 0, fileName, 0);
//	printf("-------------------------------------------------\n");

	//编码数据
	AVPacket *packet = (AVPacket*) av_malloc(sizeof(AVPacket));
	//解压缩数据
	AVFrame *frame = av_frame_alloc();

	//frame->16bit 44100 PCM统一音频采样格式与采样率
	SwrContext *swrCtx = swr_alloc();
	//重采样设置选项-----------------------------------------------------------start
	//输入的采样格式
	AVSampleFormat inSampleFmt = pCodecCtx->sample_fmt;
	//输出的采样格式
	AVSampleFormat outSampleFmt = AV_SAMPLE_FMT_S16;
	//输入的采样率
	int inSampleRate = pCodecCtx->sample_rate;
	//输出的采样率
	int outSampleRate = 44100;
	//输入的声道布局
	uint64_t inChannelLayout = pCodecCtx->channel_layout;
	//输出的声道布局：CHANNEL_IN_MONO为单声道，CHANNEL_IN_STEREO为双声道
	uint64_t outChannelLayout = AV_CH_LAYOUT_MONO;

	printf("inSampleFmt = %d, inSampleRate = %d, inChannelLayout = %d， name = %s\n", inSampleFmt, inSampleRate,
			(int) inChannelLayout, pCodec->name);

	swr_alloc_set_opts(swrCtx, outChannelLayout, outSampleFmt, outSampleRate,
			inChannelLayout, inSampleFmt, inSampleRate, 0, NULL);
	swr_init(swrCtx);
	//重采样设置选项-----------------------------------------------------------end

	//获取输出的声道个数
	int outChannelNb = av_get_channel_layout_nb_channels(outChannelLayout);
	printf("outChannelNb = %d\n", outChannelNb);

	//存储PCM数据
	uint8_t *outBuffer = (uint8_t*) av_malloc(2 * 44100);

	FILE *fp = fopen(fileName, "wb");

	//回到流的初始位置
	av_seek_frame(pFormatCtx, streamIndex, 0, AVSEEK_FLAG_BACKWARD);

	//6.一帧一帧读取压缩的音频数据AVPacket
	while (av_read_frame(pFormatCtx, packet) >= 0)
	{
		if (packet->stream_index == streamIndex)
		{
			//解码AVPacket --> AVFrame
			int ret = avcodec_send_packet(pCodecCtx, packet);
			if (ret < 0)
			{
				printf("Decode error\n");
				break;
			}

			if (avcodec_receive_frame(pCodecCtx, frame) >= 0)
			{
				swr_convert(swrCtx, &outBuffer, 2 * 44100, (const uint8_t**) frame->data, frame->nb_samples);
				//获取sample的size
				int outBufferSize = av_samples_get_buffer_size(NULL, outChannelNb, frame->nb_samples, outSampleFmt, 1);
				//写入文件
				fwrite(outBuffer, 1, outBufferSize, fp);
			}
		}

		av_packet_unref(packet);
	}

	fclose(fp);
	av_frame_free(&frame);
	av_free(outBuffer);
	swr_free(&swrCtx);
	avcodec_close(pCodecCtx);

	return 0;
}

/*
 * 视频播放命令：ffplay -video_size 654x368 -i out.yuv
 */
int avcodec_save_video_file(AVFormatContext *pFormatCtx, int streamIndex, char *fileName)
{
	AVCodec *pCodec;
	AVCodecContext *pCodecCtx;
	AVCodecParameters *codecpar = pFormatCtx->streams[streamIndex]->codecpar;

	//4.获取解码器（一）:视频
	//根据索引拿到对应的流
	pCodec = avcodec_find_decoder(codecpar->codec_id);
	if (!pCodec)
	{
		printf("can't decoder audio\n");
		return -1;
	}
	//申请一个解码上下文
	pCodecCtx = avcodec_alloc_context3(pCodec);
	if (!pCodecCtx)
	{
		printf("can't allocate a audio decoding context\n");
		return -1;
	}

	//用流解码信息初始化编码参数
	avcodec_parameters_to_context(pCodecCtx, codecpar);

	//没有此句会出现：Could not update timestamps for skipped samples
//	pCodecCtx->pkt_timebase = pFormatCtx->streams[streamIndex]->time_base;

	//5.打开解码器
	if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
	{
		printf("can't open codec\n");
		return -1;
	}

//	printf("--------------- File Information ----------------\n");
//	av_dump_format(pFormatCtx, 0, fileName, 0);
//	printf("-------------------------------------------------\n");

	//编码数据
	AVPacket *pPacket = (AVPacket*) av_malloc(sizeof(AVPacket));
	//解压缩数据
	AVFrame *pFrame = av_frame_alloc();
	AVFrame *pFrameYUV = av_frame_alloc();

	unsigned char *outBuffer = (unsigned char*) av_malloc(
			av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height, 1));
	av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize, outBuffer,
			AV_PIX_FMT_YUV420P, pCodecCtx->width,
			pCodecCtx->height, 1);

	SwsContext *pImgConvertCtx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
			pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);

	printf("width = %d, height = %d, name = %s\n", pCodecCtx->width, pCodecCtx->height, pCodec->name);

	FILE *fp = fopen(fileName, "wb+");

	//回到流的初始位置
	av_seek_frame(pFormatCtx, streamIndex, 0, AVSEEK_FLAG_BACKWARD);

	//6.一帧一帧读取压缩的视频数据AVPacket
	while (av_read_frame(pFormatCtx, pPacket) >= 0)
	{
		if (pPacket->stream_index == streamIndex)
		{
			//解码AVPacket --> AVFrame
			int ret = avcodec_send_packet(pCodecCtx, pPacket);
			if (ret < 0)
			{
				printf("Decode error\n");
				break;
			}

			if (avcodec_receive_frame(pCodecCtx, pFrame) >= 0)
			{
				sws_scale(pImgConvertCtx, pFrame->data, pFrame->linesize, 0,
						pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);

				int y_size = pCodecCtx->width * pCodecCtx->height;
				fwrite(pFrameYUV->data[0], 1, y_size, fp);    //Y
				fwrite(pFrameYUV->data[1], 1, y_size / 4, fp);  //U
				fwrite(pFrameYUV->data[2], 1, y_size / 4, fp);  //V
			}
		}

		av_packet_unref(pPacket);
	}

	fclose(fp);
	av_frame_free(&pFrame);
	av_frame_free(&pFrameYUV);
	av_free(outBuffer);
	avcodec_close(pCodecCtx);

	return 0;
}

int main(int argc, char *argv[])
{
	AVFormatContext *pFormatCtx;

	int audioStreamIndex = -1;
	int videoStreamIndex = -1;
	unsigned int i = 0;

	char inputFile[128] = "input.mp4";
	char outAudioFile[128] = "out.pcm";
	char outVideoFile[128] = "out.yuv";

	//1.注册组件
	avdevice_register_all();
	//封装格式上下文
	pFormatCtx = avformat_alloc_context();

	//2.打开输入文件
	if (avformat_open_input(&pFormatCtx, inputFile, NULL, NULL) != 0)
	{
		printf("can't open input file\n");
		return -1;
	}

	//3.获取音视频信息
	if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
	{
		printf("can't find stream info\n");
		return -1;
	}

	//音视频编码，找到对应的音视频流的索引位置
	//找到音频流的索引
	for (i = 0; i < pFormatCtx->nb_streams; ++i)
	{
		if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)
		{
			audioStreamIndex = i;
			break;
		}
	}

	//找到视频流的索引
	for (i = 0; i < pFormatCtx->nb_streams; ++i)
	{
		if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
		{
			videoStreamIndex = i;
			break;
		}
	}

	printf("audioStreamIndex = %d, videoStreamIndex = %d\n", audioStreamIndex, videoStreamIndex);

	if (audioStreamIndex == -1)
	{
		printf("can't find a audio stream\n");
	}
	else
	{
		printf("try to save audio stream\n");
		avcodec_save_audio_file(pFormatCtx, audioStreamIndex, outAudioFile);
	}

	if (videoStreamIndex == -1)
	{
		printf("can't find a video stream\n");
	}
	else
	{
		printf("try to save video stream\n");
		avcodec_save_video_file(pFormatCtx, videoStreamIndex, outVideoFile);
	}

	avformat_close_input(&pFormatCtx);

	return 0;
}

播放 

程序运行之后，后面播放音视频的时候会用到这些参数

播放音频 

ffplay -ar 44100 -ac 1 -f s16le -i out.pcm

播放视频

ffplay -video_size 654x368 -i out.yuv

 可能遇到的问题

Could not update timestamps for skipped samples

 解决办法：

pCodecCtx->pkt_timebase = pFormatCtx->streams[streamIndex]->time_base;

视频文件输出为空

解决办法：

av_seek_frame(pFormatCtx, streamIndex, 0, AVSEEK_FLAG_BACKWARD);

当然，我们可以在一个while循环里面同时处理音频和视频 

参考 

FFmpeg (libav*) 开发踩过的坑