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
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
