几种框架的比较：

https://www.zhihu.com/question/278431860

实现步骤：

1.添加依赖

implementation 'com.googlecode.mp4parser:isoparser:1.1.21'

2.视频裁剪

/**
 * 裁剪视频
 * @param srcPath 需要裁剪的原视频路径
 * @param outPath 裁剪后的视频输出路径
 * @param startTimeMs 裁剪的起始时间
 * @param endTimeMs 裁剪的结束时间
 */
public static void clip(String srcPath, String outPath, double startTimeMs, double endTimeMs) throws IOException, IllegalArgumentException {if (TextUtils.isEmpty(srcPath) || TextUtils.isEmpty(outPath)) {throw new IllegalArgumentException("file path can't be null!!!!");
    }if (!(new File(srcPath).exists())) {throw new IllegalArgumentException("the source file is not exist!!!!");
    }if (startTimeMs >= endTimeMs) {throw new IllegalArgumentException("the startTimeMs is larger than endTimeMs!!!!");
    }Movie movie = MovieCreator.build(srcPath);
    List<Track> tracks = movie.getTracks();
    //移除旧的track
    movie.setTracks(new LinkedList<Track>());
    //处理的时间以秒为单位
    double startTime = startTimeMs/1000;
    double endTime = endTimeMs/1000;
    YDLog.logDebeg(TAG, "--->>>>startTimeMs = " + startTimeMs + "\n endTimeMs = " + endTimeMs + "\n tracks.size = " + tracks.size());
    //计算剪切时间，视频的采样间隔大，以视频为准
    for (Track track : tracks) {if (track.getSyncSamples() != null && track.getSyncSamples().length > 0) {startTime = correctTimeToSyncSample(track, startTime, false);
            endTime = correctTimeToSyncSample(track, endTime, true);
            if (track.getHandler().equals("vide")) {break;
            }}}YDLog.logDebeg(TAG, "--->>>>startTime = " + startTime + "\n endTime = " + endTime);

    long currentSample;
    double currentTime;
    double lastTime;
    long startSample1;
    long endSample1;
    long delta;

    for (Track track : tracks) {currentSample = 0;
        currentTime = 0;
        lastTime = -1;
        startSample1 = -1;
        endSample1 = -1;
//根据起始时间和截止时间获取起始sample和截止sample的位置
        for (int i = 0; i < track.getSampleDurations().length; i++) {delta = track.getSampleDurations()[i];
            if (currentTime > lastTime && currentTime <= startTime) {startSample1 = currentSample;
            }if (currentTime > lastTime && currentTime <= endTime) {endSample1 = currentSample;
            }lastTime = currentTime;
            currentTime += (double)delta / (double)track.getTrackMetaData().getTimescale();
            currentSample++;
        }Log.d(TAG, "track.getHandler() = " + track.getHandler() + "\n startSample1 = " + startSample1 + "\n endSample1 = " + endSample1);
        if (startSample1 <= 0 && endSample1 <= 0) {throw new RuntimeException("clip failed !!");
        }movie.addTrack(new CroppedTrack(track, startSample1, endSample1));// 添加截取的track
    }//合成视频mp4
    Container out = new DefaultMp4Builder().build(movie);
    FileOutputStream fos = new FileOutputStream(outPath);
    FileChannel fco = fos.getChannel();
    out.writeContainer(fco);
    fco.close();
    fos.close();
}

3.视频合成

/**
 * 将 AAC 和 MP4 进行混合[替换了视频的音轨]
 *
 * @param aacPath .aac
 * @param mp4Path .mp4
 * @param outPath .mp4
 */
public static boolean muxAacMp4(String aacPath, String mp4Path, String outPath) {try {AACTrackImpl aacTrack = new AACTrackImpl(new FileDataSourceImpl(aacPath));
        Movie videoMovie = MovieCreator.build(mp4Path);
        Track videoTracks = null;// 获取视频的单纯视频部分
        for (Track videoMovieTrack : videoMovie.getTracks()) {if ("vide".equals(videoMovieTrack.getHandler())) {videoTracks = videoMovieTrack;
            }}Movie resultMovie = new Movie();
        resultMovie.addTrack(videoTracks);// 视频部分
        resultMovie.addTrack(aacTrack);// 音频部分
Container out = new DefaultMp4Builder().build(resultMovie);
        FileOutputStream fos = new FileOutputStream(new File(outPath));
        out.writeContainer(fos.getChannel());
        fos.close();
    } catch (Exception e) {e.printStackTrace();
    }return true;
}

4.合成音视频长度不一样的问题

/***
 * 把视频裁剪15s。然后和音频合并。然后再裁剪15s
 * @param sdCardPath
 */
public static void getMergeVideo(String sdCardPath) {String srcMergePath = sdCardPath + "/4.mp4";//录屏文件
    String aacPath = sdCardPath + "/5.aac";
    Log.d("peng", "onClick:  aacPath" + aacPath);
    String outMergePath = sdCardPath + "/6.mp4";//得到临时的合成的视频文件
    Log.d("peng", "onClick:  outMergePath" + outMergePath);

    long startTime = 0;
    long endTime = 15 * 1000;

    boolean isMux =  VideoClipUtils.muxAacMp4(aacPath, srcMergePath, outMergePath);

    if (isMux) {String outMergeClipPath = sdCardPath + "/7.mp4";
        Log.d("peng", "onClick:  outMergeClipPath" + outMergeClipPath);

        try {VideoClipUtils.clip(outMergePath, outMergeClipPath, startTime, endTime);
            Log.d("peng", "OKKKKKKKK");
        } catch (IOException e) {e.printStackTrace();
        }}
}

1.音频和视频合成，他们的长度

     要以视频为准的

2.合成音视频的格式，是否支持，2种方案

方案一：

先全部合并，然后再裁剪15s

方案二：(没有声音)

把视频裁剪15s。然后和音频合并。然后再裁剪15s

方案三：（导致有视频不一定有声音，或者有声音不一定有视频）

视频剪切，音频剪切，音频和视频合并

方法一：

MediaMuxer文件生成：

官方文档：

https://developer.android.google.cn/reference/android/media/MediaMuxer?hl=zh-cn

=========================================================

mp4方案：

https://blog.csdn.net/lxy_tap/article/details/74567282

http://blog.chinaunix.net/uid-20771867-id-4114253.html

使用map4parser作为视频处理包，android studio引入 compile 'com.googlecode.mp4parser:isoparser:1.1.21'//视频处理

https://blog.csdn.net/u011520181/article/details/84309734

https://www.jianshu.com/p/c87ada9b0f65

不错的库：

https://blog.csdn.net/sdvch/article/details/38348411?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param

https://github.com/sannies/mp4parser

Android(java方法）上实现mp4的分割和拼接 （二）

https://www.cnblogs.com/android-blogs/p/5711171.html