Merging or concating two mp4 Files using java

I am trying to merge two mp4 files which are having different frame rates using following code:

public class MergeMP4 {

   public static void main(String[] args) throws IOException { 

     String[] videoUris = new String[]{
                "D:/m2.mp4",
                "D:/m1.mp4"};

     List<Movie> inMovies = new ArrayList<Movie>();
        for (String videoUri : videoUris) {
            inMovies.add(MovieCreator.build(videoUri));
        }

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

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

        Movie result = new Movie();

        if (!audioTracks.isEmpty()) {
            result.addTrack(new AppendTrack(audioTracks.toArray(new Track[audioTracks.size()])));
        }
        if (!videoTracks.isEmpty()) {
            System.out.println("In Video Track");
            result.addTrack(new AppendTrack(videoTracks.toArray(new Track[videoTracks.size()])));
        }

    FileChael fc = new RandomAccessFile(String.format("D:/output.mp4"),"rw").getChael();
    new DefaultMp4Builder().build(result).writeContainer(fc);
    fc.close();
    System.out.println("Success!!");
}
}

But it able to append only audio content but video content is missing and on console it was displaying following warning messages:

Aug 30, 2016 2:25:44 PM com.googlecode.mp4parser.util.JuliLogger logError
SEVERE: BytesPerFrame differ
Aug 30, 2016 2:25:44 PM com.googlecode.mp4parser.util.JuliLogger logError
SEVERE: BytesPerSample differ
Aug 30, 2016 2:25:44 PM com.googlecode.mp4parser.util.JuliLogger logError
SEVERE: ChaelCount differ
Success!!

Please help.