Audio Sync in Videos for Nokia Devices
 

Has anyone else had problems with audio sync when converting source video (like DVD VOBs) to a video format understood by the Nokia 770 or N800 (using mencoder)?

The VOBs (and any of my resulting coverted video) contain audio/video sync correction information, which describes the time difference between frames of video and frames of audio. Most video players use this information to sync, e.g., the monitor and speaker outputs. It's usually small (less than 0.1 seconds). But mencoder likes to skip duplicate frames, adding to the sync correction value to save bits, and after a few duplicate frames, the sync correction value can start adding up.

The 770/N800 video players don't seem to use that information. Videos that sync fine when I play them in Windows can be extremely out-of-sync (as much as a second) when played on a Nokia device, implying that the Nokia video players ignore the sync correction information entirely. So when I play a video with sync correction higher than, say, 0.2 seconds, the out-of-sync'ness starts to become painfully apparent.

I've tried adding the "harddup" video filter to mencoder, which prevents mencoder from skipping duplicate frames and addresses the "accumulating sync correction" problem. But that still doesn't address any inherent sync correction the source video may have...

I don't know if this is related, but I've also noticed that videos that start out at 30fps and then switch to 24fps will play fine in Windows (the frame-rate switch occurs in the video player), but on a Nokia device, that switch never occurs, so the rest of the video runs proportionately faster than the corresponding audio. I have to use the -ofps switch to force the converted video to advertise a constant 24fps rate instead of switching in the middle.


Are there any fixes for these problems? Is there a flag in mencoder that I'm missing? Is there software that will take a sync-correction-containing video file and reduce the sync correction values to near-zero, preferably without having to re-encode the video or audio streams?

Re: Audio Sync in Videos for Nokia Devices
 

Just out of curiosity, do you see the same audio sync problems in mplayer running on 770/N800?

Re: Audio Sync in Videos for Nokia Devices
 

I've noticed this most often with converted mpeg transport streams. It seems to be worse with an increased number of video filters. The sync problem exists when playing the converted videos with mplayer on my computer, not just on an n770/n800.

EDIT:
If the material you're converting is at 24 fps ( film rate ) you may want to try a pulldown reversal filter like "-vf pullup" or "-vf softpulldown"

Re: Audio Sync in Videos for Nokia Devices
 

Some encoders seem to use fictional 120fps framerate to handle 24/30fps switching: http://www.virtualdub.org/blog/pivot/entry.php?id=103