[MPlayer-users] Fw: apparent frame dropping when playing mpeg4 part 2 es

[Tim Jebb]

Resend - didn't seem to get through?

--- On Mon, 27/9/10, Tim Jebb <jebbtr at talk21.com> wrote:

From: Tim Jebb <jebbtr at talk21.com>
Subject: apparent frame dropping when playing mpeg4 part 2 es
To: mplayer-users at mplayerhq.hu
Date: Monday, 27 September, 2010, 22:50

Hi,

I've been experimenting with capturing mpeg 4 part 2 video being produced by a camera.  It's encapsulated in RTP.  I extract the raw video data from the RTP packets into chunks (separate files)  - sequence header etc, then intra+inter frames.  I can then create arbitrary video streams by concatenating sequence header + "chunks" of intra + inter frames.  The video chunks are each one second in length.  The sequence header chunks are always identical.

The video files thus created play fine in mplayer, with one exception, which as far as I can tell is always the same:  the first three P frames in the file are not decoded.  It doesn't matter which second I start with, I'm always missing the 1st three P frames.  I can get those three frames to be decoded by starting one second earlier - in which case I'm
 missing three P frames from that earlier second and so on.  The first I frame is always present.

I tried playing the files with ffplay and as far as I can tell the error does not occur, but I don't seem to have sufficient control over eg playback frame rate to be certain.

The video is advances simple profile - I and P frames, no B frames (I checked).

Could it be some subtlety in the bitstream that I've missed, is there some timing info that mplayer's looking at causing it to ignore those frames?  I have a copy of the standard but am not an expert (am more familiar with H.264).

Any suggestions? 

Tim