[mythtv-users] A/V out of sync due to dropped frames

[Justin Gombos]

* Ian Trider <iantri at gmail.com> [2005-04-05 20:58]:
> 
> BTW, essentially if the problem you are referring to is audio sync,
> it is because of how the PVR-250 outputs streams -- the video and
> audio are aligned with via the PTS data, essentially timestaps,
> which dicates the temporal relationship between audio and video in
> an MPEG elementary stream.  If something bad happens (i.e. a frame
> drop) the PVR-250 takes no notice of it; it will be indicated in the
> PTS data and the player deals with keeping the sync locked together.
> 
> This isn't really wrong, and in fact seems like a good way to
> produce perfectly synced audio (because the temporal position of
> each frame of audio or video is indicated), but because most editing
> programs simply disregard this and work on the raw video and audio
> streams, you get 'issues' -- the lengths won't be exactly the same
> due to recording flaws (like frame drops) and it will go out of
> sync.
> 
> The way to fix it is to have a program go through and readjust lengths
> of the audio and video so that the raw streams sync properly -- by
> dropping audio or video frames to make the actual video and audio
> streams match the PTS data.

Wouldn't it be better in that case to reconstruct the missing video
frames, rather than drop audio frames?  Missing video frames can
probably be reconstructed by interpolating the 'before' and 'after'
frames, no?

BTW- I'd like to point out that this problem seems to occurr with the
Plextor tv402u.  Sometimes part way into a capture video will get
quite choppy, and audio out of sync, which is probably a symptom of
the problem you describe.  I just wanted to point that out, so folks
buying a Plextor ConvertX are aware that the bundled software is not
smart enough to resolve this problem.

Does MythTV resolve this problem?