ffmpeg从视频文件中提取音频数据

本文将从音视频mp4文件中提取对应的音频数据，并写入文件。
本人以霍乱时期的爱情电影为题材，提取里面的音频；整个mp4文件为1.69G大小，时长两个小时12分41秒，提取的音频数据生成的音频文件的大小为123兆，时长两个小时12分41秒。

注意，本人只提取了一路音频，不涉及mp4里面多路音频的情况。

提取过程也简单，就不说明了。

代码结构如下：

其中main函数所在文件FfmpegExtractAudio内容如下:

#include <iostream>
#include "ExtractAudio.h"
#include <vector>#ifdef   __cplusplus
extern "C"
{#endif#pragma comment(lib, "avcodec.lib")
#pragma comment(lib, "avformat.lib")
#pragma comment(lib, "avutil.lib")
#pragma comment(lib, "avdevice.lib")
#pragma comment(lib, "avfilter.lib")
#pragma comment(lib, "postproc.lib")
#pragma comment(lib, "swresample.lib")
#pragma comment(lib, "swscale.lib")#ifdef __cplusplus
};
#endifint main()
{CExtractAudio cCExtractAudio;const char *pFileA = "E:\\ffmpeg\\convert\\huoluan.mp4";const char *pFileOut = "E:\\learn\\ffmpeg\\FfmpegGifTest\\x64\\Release\\huoluan3_audio_extract.mp4";cCExtractAudio.StartExtractAudio(pFileA, pFileOut);cCExtractAudio.WaitFinish();return 0;
}

ExtractAudio.h的内容如下：

#pragma once#include <Windows.h>#ifdef __cplusplus
extern "C"
{#endif
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"
#include "libavdevice/avdevice.h"
#include "libavutil/audio_fifo.h"
#include "libavutil/avutil.h"
#include "libavutil/fifo.h"
#include "libavutil/frame.h"
#include "libavutil/imgutils.h"#include "libavfilter/avfilter.h"
#include "libavfilter/buffersink.h"
#include "libavfilter/buffersrc.h"#ifdef __cplusplus
};
#endifclass CExtractAudio
{public:CExtractAudio();~CExtractAudio();
public:int StartExtractAudio(const char *pFileA, const char *pFileOut);int WaitFinish();
private:int OpenFileA(const char *pFileA);int OpenOutPut(const char *pFileOut);
private:static DWORD WINAPI FileAReadProc(LPVOID lpParam);void FileARead();static DWORD WINAPI ExtractAudioProc(LPVOID lpParam);void ExtractAudio();
private:AVFormatContext *m_pFormatCtx_FileA = NULL;AVCodecContext *m_pReadCodecCtx_AudioA = NULL;AVCodec *m_pReadCodec_AudioA = NULL;AVCodecContext  *m_pCodecEncodeCtx_Audio = NULL;AVFormatContext *m_pFormatCtx_Out = NULL;AVAudioFifo      *m_pAudioAFifo = NULL;
private:CRITICAL_SECTION m_csAudioASection;HANDLE m_hFileAReadThread = NULL;HANDLE m_hExtractAudioThread = NULL;AVRational m_streamTimeBase;SwrContext *m_pAudioConvertCtx = NULL;int m_iAudioStreamIndex = 0;
};

ExtractAudio.cpp的内容如下：


#include "ExtractAudio.h"
//#include "log/log.h"CExtractAudio::CExtractAudio()
{InitializeCriticalSection(&m_csAudioASection);
}CExtractAudio::~CExtractAudio()
{DeleteCriticalSection(&m_csAudioASection);
}int CExtractAudio::StartExtractAudio(const char *pFileA, const char *pFileOut)
{int ret = -1;do{ret = OpenFileA(pFileA);if (ret != 0){break;}ret = OpenOutPut(pFileOut);if (ret != 0){break;}m_pAudioAFifo = av_audio_fifo_alloc((AVSampleFormat)m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->format,m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->channels, 3000 * 1024);int iSrcChLayout = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->channel_layout;int iDstChLayout = m_pFormatCtx_Out->streams[0]->codecpar->channel_layout;int iSrcSampleRate = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->sample_rate;int iDstSampleRate = m_pFormatCtx_Out->streams[0]->codecpar->sample_rate;int iSrcFmt = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->format;int iDstFmt = m_pFormatCtx_Out->streams[0]->codecpar->format;m_pAudioConvertCtx = swr_alloc();av_opt_set_channel_layout(m_pAudioConvertCtx, "in_channel_layout", iSrcChLayout, 0);av_opt_set_channel_layout(m_pAudioConvertCtx, "out_channel_layout", iDstChLayout, 0);av_opt_set_int(m_pAudioConvertCtx, "in_sample_rate", iSrcSampleRate, 0);av_opt_set_int(m_pAudioConvertCtx, "out_sample_rate", iDstSampleRate, 0);av_opt_set_sample_fmt(m_pAudioConvertCtx, "in_sample_fmt", (AVSampleFormat)iSrcFmt, 0);av_opt_set_sample_fmt(m_pAudioConvertCtx, "out_sample_fmt", (AVSampleFormat)iDstFmt, 0);ret = swr_init(m_pAudioConvertCtx);m_hFileAReadThread = CreateThread(NULL, 0, FileAReadProc, this, 0, NULL);m_hExtractAudioThread = CreateThread(NULL, 0, ExtractAudioProc, this, 0, NULL);} while (0);return ret;
}int CExtractAudio::WaitFinish()
{int ret = 0;do{if (NULL == m_hFileAReadThread){break;}WaitForSingleObject(m_hFileAReadThread, INFINITE);CloseHandle(m_hFileAReadThread);m_hFileAReadThread = NULL;WaitForSingleObject(m_hExtractAudioThread, INFINITE);CloseHandle(m_hExtractAudioThread);m_hExtractAudioThread = NULL;} while (0);return ret;
}int CExtractAudio::OpenFileA(const char *pFileA)
{int ret = -1;do{if ((ret = avformat_open_input(&m_pFormatCtx_FileA, pFileA, 0, 0)) < 0) {printf("Could not open input file.\n");break;}if ((ret = avformat_find_stream_info(m_pFormatCtx_FileA, 0)) < 0) {printf("Failed to retrieve input stream information\n");break;}for (int i = 0; i < m_pFormatCtx_FileA->nb_streams; i++){if (m_pFormatCtx_FileA->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO){m_streamTimeBase = m_pFormatCtx_FileA->streams[i]->time_base;m_pReadCodec_AudioA = (AVCodec *)avcodec_find_decoder(m_pFormatCtx_FileA->streams[i]->codecpar->codec_id);m_pReadCodecCtx_AudioA = avcodec_alloc_context3(m_pReadCodec_AudioA);if (m_pReadCodecCtx_AudioA == NULL){break;}avcodec_parameters_to_context(m_pReadCodecCtx_AudioA, m_pFormatCtx_FileA->streams[i]->codecpar);if (avcodec_open2(m_pReadCodecCtx_AudioA, m_pReadCodec_AudioA, NULL) < 0){break;}m_iAudioStreamIndex = i;ret = 0;break;}}} while (0);return ret;
}int CExtractAudio::OpenOutPut(const char *pFileOut)
{int iRet = -1;AVStream *pAudioStream = NULL;do{avformat_alloc_output_context2(&m_pFormatCtx_Out, NULL, NULL, pFileOut);{AVCodec* pCodecEncode_Audio = (AVCodec *)avcodec_find_encoder(m_pFormatCtx_Out->oformat->audio_codec);m_pCodecEncodeCtx_Audio = avcodec_alloc_context3(pCodecEncode_Audio);if (!m_pCodecEncodeCtx_Audio){break;}pAudioStream = avformat_new_stream(m_pFormatCtx_Out, pCodecEncode_Audio);if (!pAudioStream){break;}m_pCodecEncodeCtx_Audio->sample_rate = m_pReadCodecCtx_AudioA->sample_rate;m_pCodecEncodeCtx_Audio->channel_layout = m_pReadCodecCtx_AudioA->channel_layout;m_pCodecEncodeCtx_Audio->channels = av_get_channel_layout_nb_channels(m_pCodecEncodeCtx_Audio->channel_layout);m_pCodecEncodeCtx_Audio->sample_fmt = (AVSampleFormat)m_pReadCodecCtx_AudioA->sample_fmt;if (m_pFormatCtx_Out->oformat->flags & AVFMT_GLOBALHEADER)m_pCodecEncodeCtx_Audio->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;if (avcodec_open2(m_pCodecEncodeCtx_Audio, pCodecEncode_Audio, 0) < 0){//编码器打开失败，退出程序break;}}if (!(m_pFormatCtx_Out->oformat->flags & AVFMT_NOFILE)){if (avio_open(&m_pFormatCtx_Out->pb, pFileOut, AVIO_FLAG_WRITE) < 0){break;}}avcodec_parameters_from_context(pAudioStream->codecpar, m_pCodecEncodeCtx_Audio);if (avformat_write_header(m_pFormatCtx_Out, NULL) < 0){break;}iRet = 0;} while (0);if (iRet != 0){if (m_pCodecEncodeCtx_Audio != NULL){avcodec_free_context(&m_pCodecEncodeCtx_Audio);m_pCodecEncodeCtx_Audio = NULL;}if (m_pFormatCtx_Out != NULL){avformat_free_context(m_pFormatCtx_Out);m_pFormatCtx_Out = NULL;}}return iRet;
}DWORD WINAPI CExtractAudio::FileAReadProc(LPVOID lpParam)
{CExtractAudio *pExtractAudio = (CExtractAudio *)lpParam;if (pExtractAudio != NULL){pExtractAudio->FileARead();}return 0;
}void CExtractAudio::FileARead()
{AVFrame *pFrame;pFrame = av_frame_alloc();AVPacket packet = { 0 };int ret = 0;while (1){av_packet_unref(&packet);ret = av_read_frame(m_pFormatCtx_FileA, &packet);if (ret == AVERROR(EAGAIN)){continue;}else if (ret == AVERROR_EOF){break;}else if (ret < 0){break;}if (packet.stream_index != m_iAudioStreamIndex){continue;}ret = avcodec_send_packet(m_pReadCodecCtx_AudioA, &packet);if (ret >= 0){ret = avcodec_receive_frame(m_pReadCodecCtx_AudioA, pFrame);if (ret == AVERROR(EAGAIN)){continue;}else if (ret == AVERROR_EOF){break;}else if (ret < 0) {break;}while (1){int buf_space = av_audio_fifo_space(m_pAudioAFifo);if (buf_space >= pFrame->nb_samples){EnterCriticalSection(&m_csAudioASection);ret = av_audio_fifo_write(m_pAudioAFifo, (void **)pFrame->data, pFrame->nb_samples);LeaveCriticalSection(&m_csAudioASection);break;}else{Sleep(100);}}}if (ret == AVERROR(EAGAIN)){continue;}}av_frame_free(&pFrame);
}DWORD WINAPI CExtractAudio::ExtractAudioProc(LPVOID lpParam)
{CExtractAudio *pExtractAudio = (CExtractAudio *)lpParam;if (pExtractAudio != NULL){pExtractAudio->ExtractAudio();}return 0;
}void CExtractAudio::ExtractAudio()
{int ret = 0;AVFrame *pFrameAudioA = av_frame_alloc();pFrameAudioA->nb_samples = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->frame_size > 0 ? m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->frame_size : 1024;pFrameAudioA->channel_layout = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->channel_layout;pFrameAudioA->format = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->format;pFrameAudioA->sample_rate = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->sample_rate;pFrameAudioA->channels = m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->channels;av_frame_get_buffer(pFrameAudioA, 0);AVPacket packet = { 0 };int iAudioFrameIndex = 0;while (1){if (NULL == m_pAudioAFifo){break;}if (av_audio_fifo_size(m_pAudioAFifo) >=(m_pFormatCtx_Out->streams[0]->codecpar->frame_size > 0 ? m_pFormatCtx_Out->streams[0]->codecpar->frame_size : 1024)){EnterCriticalSection(&m_csAudioASection);int readcount = av_audio_fifo_read(m_pAudioAFifo, (void **)pFrameAudioA->data,(m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->frame_size > 0 ? m_pFormatCtx_FileA->streams[m_iAudioStreamIndex]->codecpar->frame_size : 1024));LeaveCriticalSection(&m_csAudioASection);ret = avcodec_send_frame(m_pCodecEncodeCtx_Audio, pFrameAudioA);if (ret == AVERROR(EAGAIN)){continue;}ret = avcodec_receive_packet(m_pCodecEncodeCtx_Audio, &packet);if (ret == AVERROR(EAGAIN)){continue;}packet.stream_index = 0;packet.pts = iAudioFrameIndex * m_pFormatCtx_Out->streams[0]->codecpar->frame_size;packet.dts = iAudioFrameIndex * m_pFormatCtx_Out->streams[0]->codecpar->frame_size;packet.duration = m_pFormatCtx_Out->streams[0]->codecpar->frame_size;ret = av_write_frame(m_pFormatCtx_Out, &packet);iAudioFrameIndex++;}else{if (m_hFileAReadThread == NULL){break;}Sleep(1);}}av_write_trailer(m_pFormatCtx_Out);avio_close(m_pFormatCtx_Out->pb);av_frame_free(&pFrameAudioA);
}

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