将 H264 + PCMA 转为MP4格式（RTSP协议）

问题：

通过rtsp交互，解析RTP流（h264视频+alaw(pcma)音频），将其保存为MP4格式。

解决方案：

使用MP4V2 ，版本2.0.0， VC2010可编译。（还有一种gpac库，听说支持h265，未实验）

Mp4V2下载地址： https://code.google.com/archive/p/mp4v2/downloads ，文件名mp4v2-2.0.0.tar.bz2

参考文章：使用mp4v2将H264+AAC合成mp4文件

参考文章：将RTSP流录制为mp4文件

参考文章： linux下利用mp4v2库将h264和aac文件封装成MP4

参考文章： Android音视频系列：视频容器操作篇 -- mp4容器打包实现

参考文章： Mp4V2调试经验记录（视频或者音画同步的主要参数是duration）

参考文章：mp4v2 接口函数：其中有一些注意的地方，我似乎没有理会。

PS：考虑过FFmpeg，但是太大，Windows下编译麻烦，不会裁剪。Mp4V2比较轻量级，适合做一个SDK。

前期：

建议先对MP4格式有一点基本了解，看看一些MP4格式的文档，有一个基本概念。

参考文章： mp4文件格式解析，介绍详细，其中推荐mp4v2 和 gpac，和一个在线MP4格式解析器，

参考文章（代码）：逐个Box解析MP4文件的代码，挺好的。 MP4 file analyzer （This is a console application, written by MSVC 2008.It will display mp4 file content in human readable format.）

套路：


//创建mp4文件
MP4FileHandle file = MP4CreateEx("d:\\test.mp4", MP4_CREATE_64BIT_DATA | MP4_CREATE_64BIT_TIME);MP4SetTimeScale(file, 90000);MP4TrackId video = MP4AddH264VideoTrack(file, 90000, 90000/_fps, _width, _height,0x64, //sps[1] AVCProfileIndication0x00, //sps[2] profile_compat0x1f, //sps[3] AVCLevelIndication3); // 4 bytes length before each NAL unit
MP4SetVideoProfileLevel(file, 0x7F);//源码重新编译，新加函数MP4AddALawAudioTrack2
MP4TrackId audio = MP4AddALawAudioTrack2(file,8000,   //timescale8000*40/1000);   //sampleDuration.  40msMP4SetTrackIntegerProperty(file,audio, "mdia.minf.stbl.stsd.alaw.channels",1);
MP4SetAudioProfileLevel(file, 0x2);while(1)
{//更新SPSMP4AddH264SequenceParameterSet(file, video, (const uint8_t*)(pH264+4), len);//更新PPSMP4AddH264PictureParameterSet(file, video, (const uint8_t*)(pH264+4), len);//更新H264 (前四个字节需要特殊处理)if(key_frame){MP4WriteSample(file, video, (const uint8_t* )pH264, len, MP4_INVALID_DURATION, 0, 1);}else{MP4WriteSample(file, video, (const uint8_t* )pH264, len, MP4_INVALID_DURATION, 0, 0);}//更新pcmaMP4WriteSample(file, audio, (const uint8_t* )pCMA, len , MP4_INVALID_DURATION, 0, 1);}MP4Close(file);

PS: 注意Write H264 Sample时，h264流中的NAL，头四个字节是0x00000001，而mp4中的h264track，头四个字节要求是NAL的长度，并且是大端顺序，所以，写入前，需要进行如下更改：

uint32_t* pSize = (uint32_t*)pH264 ;
*pSize = htonl(len - 4);

PS: 源码中函数 AddALawAudioTrack里面计算

uint32_t fixedSampleDuration = (timeScale * 20)/1000; // 20mSec/Sample

然而实际的1秒25帧，间隔40ms，而不是20ms。故而需要手动添加一个新的接口。

PS: 音频和视频同步没有特别处理，没考虑。

PS: SPS，PPS 不知道是否需要每次变更都需要进行 MP4AddH264SequenceParameterSet ， MP4AddH264PictureParameterSet操作。不确定这个操作的影响。

简单实验结果：

测试步骤1 : VLC可播放, 有声音。

测试步骤2：手机端微信可播放。

测试步骤3：桌面端微信不可播放。（猜测可能是音频格式需要AAC格式）

测试步骤4： Html5 可播放，有声音。

测试步骤5： Windows Media Player可播放，但是没声音。

困扰：发现MP4文件中的mdat 数据特别长，不知道是否有影响，这份生成的MP4文件不支持格式工厂转换。

其他：

感觉MP4似乎主要用来打包H264和AAC的，而我用的音频是PCMA，不知道有没有兼容性问题。

mp4格式好复杂，结构可变，又多, 里面有好多Box结构体，我曾经企图一个字节一个字节的研究，后来放弃了，复杂。

附图（图片来自网络）：

参考源码：（来源： https://github.com/Thinkerfans/lib-mp4v2/tree/master/mp4v2）

lib-mp4v2/mp4v2/mp4record.h

//
//  mp4record.h
//  RTSP_Player
//
//  Created by apple on 15/4/7.
//  Copyright (c) 2015年 thinker. All rights reserved.
//#ifndef __RTSP_Player__mp4record__
#define __RTSP_Player__mp4record__#include "mp4v2.h"#define  _NALU_SPS_  0
#define  _NALU_PPS_  1
#define  _NALU_I_    2
#define  _NALU_P_    3int initMp4Encoder(const char * filename,int width,int height);
int mp4VEncode(uint8_t * data ,int len);
int mp4AEncode(uint8_t * data ,int len);
void closeMp4Encoder();#endif /* defined(__RTSP_Player__mp4record__) */

lib-mp4v2/mp4v2/mp4record.c

//
//  mp4record.c
//  RTSP_Player
//
//  Created by apple on 15/4/7.
//  Copyright (c) 2015年 thinker. All rights reserved.
//#include "mp4record.h"
#include <stdlib.h>typedef struct MP4V2_CONTEXT{int m_vWidth,m_vHeight,m_vFrateR,m_vTimeScale;MP4FileHandle m_mp4FHandle;MP4TrackId m_vTrackId,m_aTrackId;double m_vFrameDur;} MP4V2_CONTEXT;struct MP4V2_CONTEXT * recordCtx = NULL;int initMp4Encoder(const char * filename,int width,int height){int ret = -1;recordCtx = malloc(sizeof(struct MP4V2_CONTEXT));if (!recordCtx) {printf("error : malloc context \n");return ret;}recordCtx->m_vWidth = width;recordCtx->m_vHeight = height;recordCtx->m_vFrateR = 25;recordCtx->m_vTimeScale = 90000;recordCtx->m_vFrameDur = 300;recordCtx->m_vTrackId = 0;recordCtx->m_aTrackId = 0;recordCtx->m_mp4FHandle = MP4Create(filename,0);if (recordCtx->m_mp4FHandle == MP4_INVALID_FILE_HANDLE) {printf("error : MP4Create  \n");return ret;}MP4SetTimeScale(recordCtx->m_mp4FHandle, recordCtx->m_vTimeScale);//------------------------------------------------------------------------------------- audio track
//    recordCtx->m_aTrackId = MP4AddAudioTrack(recordCtx->m_mp4FHandle, 44100, 1024, MP4_MPEG4_AUDIO_TYPE);
//    if (recordCtx->m_aTrackId == MP4_INVALID_TRACK_ID){
//        printf("error : MP4AddAudioTrack  \n");
//        return ret;
//    }
//
//    MP4SetAudioProfileLevel(recordCtx->m_mp4FHandle, 0x2);
//    uint8_t aacConfig[2] = {18,16};
//    MP4SetTrackESConfiguration(recordCtx->m_mp4FHandle,recordCtx->m_aTrackId,aacConfig,2);
//    printf("ok  : initMp4Encoder file=%s  \n",filename);return 0;
}
int mp4VEncode(uint8_t * _naluData ,int _naluSize){int index = -1;if(_naluData[0]==0 && _naluData[1]==0 && _naluData[2]==0 && _naluData[3]==1 && _naluData[4]==0x67){index = _NALU_SPS_;}if(index!=_NALU_SPS_ && recordCtx->m_vTrackId == MP4_INVALID_TRACK_ID){return index;}if(_naluData[0]==0 && _naluData[1]==0 && _naluData[2]==0 && _naluData[3]==1 && _naluData[4]==0x68){index = _NALU_PPS_;}if(_naluData[0]==0 && _naluData[1]==0 && _naluData[2]==0 && _naluData[3]==1 && _naluData[4]==0x65){index = _NALU_I_;}if(_naluData[0]==0 && _naluData[1]==0 && _naluData[2]==0 && _naluData[3]==1 && _naluData[4]==0x41){index = _NALU_P_;}//switch(index){case _NALU_SPS_:if(recordCtx->m_vTrackId == MP4_INVALID_TRACK_ID){recordCtx->m_vTrackId = MP4AddH264VideoTrack(recordCtx->m_mp4FHandle,recordCtx->m_vTimeScale,recordCtx->m_vTimeScale / recordCtx->m_vFrateR,recordCtx->m_vWidth,     // widthrecordCtx->m_vHeight,    // height_naluData[5], // sps[1] AVCProfileIndication_naluData[6], // sps[2] profile_compat_naluData[7], // sps[3] AVCLevelIndication3);           // 4 bytes length before each NAL unitif (recordCtx->m_vTrackId == MP4_INVALID_TRACK_ID)  {return -1;}MP4SetVideoProfileLevel(recordCtx->m_mp4FHandle, 0x7F); //  Simple Profile @ Level 3}MP4AddH264SequenceParameterSet(recordCtx->m_mp4FHandle,recordCtx->m_vTrackId,_naluData+4,_naluSize-4);//break;case _NALU_PPS_:MP4AddH264PictureParameterSet(recordCtx->m_mp4FHandle,recordCtx->m_vTrackId,_naluData+4,_naluSize-4);break;case _NALU_I_:{uint8_t * IFrameData = malloc(_naluSize+1);//IFrameData[0] = (_naluSize-3) >>24;IFrameData[1] = (_naluSize-3) >>16;IFrameData[2] = (_naluSize-3) >>8;IFrameData[3] = (_naluSize-3) &0xff;memcpy(IFrameData+4,_naluData+3,_naluSize-3);
//            if(!MP4WriteSample(recordCtx->m_mp4FHandle, recordCtx->m_vTrackId, IFrameData, _naluSize+1, recordCtx->m_vFrameDur/44100*90000, 0, 1)){
//                return -1;
//            }
//            recordCtx->m_vFrameDur = 0;if(!MP4WriteSample(recordCtx->m_mp4FHandle, recordCtx->m_vTrackId, IFrameData, _naluSize+1, MP4_INVALID_DURATION, 0, 1)){return -1;}free(IFrameData);//break;}case _NALU_P_:{_naluData[0] = (_naluSize-4) >>24;  _naluData[1] = (_naluSize-4) >>16;  _naluData[2] = (_naluSize-4) >>8;  _naluData[3] = (_naluSize-4) &0xff;//            if(!MP4WriteSample(recordCtx->m_mp4FHandle, recordCtx->m_vTrackId, _naluData, _naluSize, recordCtx->m_vFrameDur/44100*90000, 0, 1)){
//                return -1;
//            }
//            recordCtx->m_vFrameDur = 0;if(!MP4WriteSample(recordCtx->m_mp4FHandle, recordCtx->m_vTrackId, _naluData, _naluSize, MP4_INVALID_DURATION, 0, 1)){return -1;}break;}}return 0;
}int mp4AEncode(uint8_t * data ,int len){if(recordCtx->m_vTrackId == MP4_INVALID_TRACK_ID){return -1;}MP4WriteSample(recordCtx->m_mp4FHandle, recordCtx->m_aTrackId, data, len , MP4_INVALID_DURATION, 0, 1);recordCtx->m_vFrameDur += 1024;return 0;
}void closeMp4Encoder(){if(recordCtx){if (recordCtx->m_mp4FHandle != MP4_INVALID_FILE_HANDLE) {MP4Close(recordCtx->m_mp4FHandle,0);recordCtx->m_mp4FHandle = NULL;}free(recordCtx);recordCtx = NULL;}printf("ok  : closeMp4Encoder  \n");}