Intermittent Audio/Video Sync hiccups after Demuxing

[nagha]

hi,

i have a wedding DVD that i wanted to add chapters and menus to - my videographer sucks!

so, i ripped the DVD to my computer, demuxed it using MPEG Streamclip, fixed the time errors, converted it into unheaded MP2/AC3 (audio originally AC3) and then did the work i needed in DVDSP3.

the problem is that every 30-45 seconds, there are hiccups where the audio is mismatched for a fraction of a second and then resyncs. everything is in sync at all other times. it's like a record skipping periodically.

any suggestions/insight would be greatly appreciated.

na

[alph]

I don't have all the answers, but I'm a little confused about what you did in Streamclip. Mostly, fixing time errors after demuxing seems like it could cause sync problems.

If you are using MPEG Streamclip 1.2, and indeed you need to demux for your uses in DVDSP3, all it seems to me you need to do is use the "Demux to m2v and ac3..." command. By default when a demux, convert, or export command is used a "fix streams with data breaks" is run, as set in the preferences.

Cheers,
Alph

[havema-1]

At first I thought that it might be good to always enable MPEG Streamclip's preference "Fix streams with data breaks".

I asked this from the MPEG Streamclip author. Although there is no "significant" speed penalty in routinely enabling "Fix streams with data breaks", it is not recommended for everyone to enable this option without reason because it may further damage some slightly incorrect MPEG files. And it does nothing with well-authored VOB files.

However, I do often choose Edit/Fix Timecode Breaks... so the combined length of the MPEGs is reported. I got also info about the difference between "Save as" and "Convert to" commands which seem similar when dealing with MPEG-only files but often it is best to use the latter:

"Save As" simply makes a copy of the file, while "Convert to" passes the file through the internal remultiplexer. "Save As" does not change the structure of the file (and does not save fixed timecode, at least in version 1.2), while "Convert to" changes many things, fixes timecode, and also drops everything but one video and one audio track.

However there are two cases in which Save As behaves like "Convert to": 1. you have edited the stream with Cut; 2. the source file is a demuxed M2V file. In these cases, the resulting file will be identical for "Save As" and "Convert to"; if you use Save As in these cases, the progress window will say "Converting" instead of "Copying" and the batch list will report "Convert to" instead of "Save As".

[nagha]

I tired yade X (yet another DVD decoder) and it worked perfectly. i suspect it had something to do with how Streamclip fixes the time codes that caused the problem. in retrospect, there must be a problem with the source DVD because i see glitches in the time counter that are at the same places as the previous hiccups but with yade X, the audio stays in sync.

thanks,
Neema

[alph]

Yade and MPEG Streamclip are 2 different things. Streamclip is an MPEG editor and Yade is a DVD ripper. Yade has ripping features that Streamclip does not. I suspect using Streamclip to rip a DVD could lead to sync problems.

hmm,
Alph :O)

[sjk]

Perfect timing with that info, havema-1 -- thanks! It's exactly what I wanted to know when using MPEG Streamclip to combine multiple VOB files into a single MPEG-2 file for EyeHome playback. Still figuring out what'll work best for preserving only the specific audio track(s) I'm interested in.

[maetel99]

MPEG Streamclip uses Apple's QuickTime MPEG-2 Playback component to do its video decoding. Unfortunately, Apple's component is notoriously buggy and frequently gets the frame rate wrong, leading to sync problems. Apple has shown no interest in fixing things for at least the last two years, and I understand that the fellow who wrote that component left the company a while back.

YadeX uses the open source libmpeg2 to do the decoding and that may work better in some cases, but I would bet that it also will get out of sync if you have a DVD with variable frame rate video. This is unfortunately getting rather common, especially with music videos and discs from DVD recorders.

If you want something that actually works reliably to keep things in sync, you'll have to go for a commercial product. Try Cinematize.

[sjk]

Thanks for the reminder about QuickTime MPEG-2 Playback component being "notoriously buggy". I'll remember that if Apple tries charging another $20 for it with QuickTime 7 while it remains buggy. So far I've avoided frame rate or sync problems with it and MPEG Streamclip but my usage has been pretty basic and conservative.