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

旧城等待， 2021-09-24 04:00 1763阅读 0赞

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 <stdio.h>
    
    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

![20200416155857278.png][]

## 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 ##