MPEG4/AC3 videos saved as Self-Contained MOV files are out of sync

[cooperaa]

Hello,

I've done some searching to find out if anyone is having similar problems as me, but while I found some sync-related posts none seemed to be the particular problem I'm experiencing.

I've downloaded several AVI videos with XVID video streams and AC3 audio streams. The original AVI files play fine with QuickTime/VLC/etc, but when I save the files as "self-contained movie files" (so that I can add them to my iTunes library) the audio starts getting ahead of the video after a few seconds. If I pause and then continue playback, the video jumps back into sync and then is out of sync a few seconds later.

I've also downloaded some AVI files with XVID video streams and MP3 audio streams and they *don't* get out of sync. The problem seems to be with the AC3 audio streams.

I have Perian 1.1.2 installed.

To add to the bizarreness, I've got some MKV files with H.264 video streams and AC3 audio streams that *don't* get out of sync. They play fine. So I guess it's some combination of XVID/MPEG-4 and AC3 streams that are causing me grief.

Could it possibly be codecs that I've got installed that are the issue or does anyone else have issue creating self-contained movies with MPEG4/AC3 streams?

[tomlee59]

Actually, your problems are more related to CPU/disk/ram performance issues. When you save as a "self-contained movie," the computer has to work hard to parse the video from the audio, and decode each separately. Audio being easy to decode that stays in sync, but the video gets further and further behind. Pausing and restarting lets the system start afresh, but lags as time goes on.

You could try backing off on video bit rates. Or get a faster computer. If you're low on RAM, take it to the max. That can help performance tremendously.

[cooperaa]

I mentioned that videos with MP3 audio stay in sync though (they have relatively the same video bitrates - ~1 Mbps video, 192 kbps audio).

Also, the 720p MKV files with H.264/AC3 streams have considerably higher bitrates and play fine (~3 Mbps video and 384 kbps audio).

My computer can also play ~8 Mbps 1080p MKV files, so I don't think it's a performance issue.

[tomlee59]

I agree -- now that you've provided some bitrate values for the various combinations, it would seem unlikely that it was a straightforward computer performance issue. Your original hypothesis that it is some odd combination of XviD and AC3 that is the problem looks pretty likely. Unfortunately, I haven't encountered that particular problem, so I don't have any useful suggestions for you on how to fix it directly. However, one possible workaround would be for you to transcode the AC3 audio into MP3, and then use the latter instead of the former in the self-contained .mov, since that combination seems to be ok.