Code used to append 4 mp4 files using mp4parser - Code uses example path to file strings.

mp4parser_append_example

            try {

                final Movie intro = MovieCreator.build(new FileDataSourceImpl(file1));
                final Movie main = MovieCreator.build(new FileDataSourceImpl(file2));
                final Movie resultClip = MovieCreator.build(new FileDataSourceImpl(file3));
                final Movie end = MovieCreator.build(new FileDataSourceImpl(file4));

                final Movie[] movies = new Movie[]{intro, main, resultClip, end};

                final List<Track> videoTracks = new LinkedList<>();
                final List<Track> audioTracks = new LinkedList<>();

                for (Movie m : movies) {
                    for (Track track : m.getTracks()) {
                        if (track.getHandler().equals("soun")) {
                            audioTracks.add(track);
                        }
                        if (track.getHandler().equals("vide")) {
                            videoTracks.add(track);
                        }
                    }
                }

                final Movie output = new Movie();

                if (videoTracks.size() > 0) {
                    output.addTrack(new AppendTrack(videoTracks.toArray(new Track[videoTracks.size()])));
                }

                if (audioTracks.size() > 0) {
                    output.addTrack(new AppendTrack(audioTracks.toArray(new Track[audioTracks.size()])));
                }

                final Container container = new DefaultMp4Builder().build(output);
                final RandomAccessFile randomAccessFile = new RandomAccessFile(finalOutput, "rw");

                final FileChannel fileChannel = randomAccessFile.getChannel();
                container.writeContainer(fileChannel);
                randomAccessFile.close();
                fileChannel.close();

                Timber.d("SUCCESS!");

            } catch (IOException e) {
                e.printStackTrace();
            }