MP4和MP3的合成

目标，将MP3中的声音合成到MP4中去。

采用的第三方库:MP4Parser,

Muxing Audio/Video

The API and the process is straight-forward:

1. You wrap each raw format file into an appropriate Track object. 

   H264TrackImpl h264Track = new H264TrackImpl(new FileDataSourceImpl("video.h264"));
   AACTrackImpl aacTrack = new AACTrackImpl(new FileDataSourceImpl("audio.aac"));

2. These Track object are then added to a Movie object

   Movie movie = new Movie();
   movie.addTrack(h264Track);
   movie.addTrack(aacTrack);

3. The Movie object is fed into an MP4Builder to create the container. 

   Container mp4file = new DefaultMp4Builder().build(movie);

4. Write the container to an appropriate sink.

   FileChannel fc = new FileOutputStream(new File("output.mp4")).getChannel();
   mp4file.writeContainer(fc);
   fc.close();

要求.h264文件和aac文件的作为“输入”， 输出为mp4格式。

测试：使用MediaRecorder生成后缀为.H264的文件。测试可以在手机端播放。使用以上方法与一个aac文件合成。报错：

java.lang.NullPointerException: Attempt to read from field 'int com.googlecode.mp4parser.h264.model.PictureParameterSet.seq_parameter_set_id' on a null object reference

h264Track = new H264TrackImpl(new FileDataSourceImpl("/storage/emulated/0/DCIM/TestCamera/VID_2016.H264"));//报错行

构造失败。谷歌该问题无果。

查看mp4parser的issues:

Combine a music.m4a on a video.mp4 overwrite my video audio

mp4parser的作者回复：

“Basically you want to merge two audio tracks to one. Players won't play two audio tracks at the same time. This is a use case that requires decoding, then merging and encoding into one audio track again. The MP4parser cannot do that. I guess you'll need to use ffmpeg or the MediaCodec API.”

一句话，mp4parser做不到。