Android - Playing Mp4

I am trying to play video files from http urls in my app. Why is that my app plays only certain mp4 files (I tried 512k mp4 and it worked), and doesn't play some others?

Here's the snippet of my code:

    mVideoView.setVideoPath(myVideoURL);    mVideoView.setMediaController(new MediaController(this));    mVideoView.seekTo(currentPosition);    mVideoView.requestFocus(); 

ThanksChris