audio sync

[DeusExMachina]

People periodically post questions about audio sync issues and now I wish I had paid more attention to the answers. I have a bunch of MPEG-1 VCD files I want to offload to DVD. Most import into DVDSP just fine, but a few come in with audio sync problems after being demuxed and the audio re-encoded into AC3 with ffmpegX. The audio is faster than the video, and develops progressively worse audio sync.
Audio is originally mp2 41k 224kb/s, converted to 48k 256kb/s AC3.

[TugBoat]

Audio is originally mp2 41k 224kb/s, converted to 48k 256kb/s AC3.

Converting sampling rates with ffmpegX is not wise. Unless things have changed recently...
I would suggest using iTunes to convert the 41kHz MP2 Audio to 48kHz AIFF, then use Compressor (if you have DVDSP, you should have Compressor) to convert to AC3.

If that doesn't cure it, then look at;
https://forum.videohelp.com/viewtopic.php?t=308561

[DeusExMachina]

Thanks.
Actually, I ended up solving it, but through a different route. Turns out the issue was related to the demuxing, and the differences between how ffmpeg and MPEGstream clip generate the demuxed files. They were out of sync using the m2v file generated from MPEGstreamclip, but matched fine in the m1v file generated by ffmpegX. Still not quite clear what determines the naming conventions, being that even ffmpegX declares MPEG-1 sources as MPEG-2, in spite of saving it as m1v.

One question for you, though. Why do you suggest not using VBR audio? I have never had an issue with it in conversion of files for use in DVDs.

[TugBoat]

I probably don't like VBR MP3s in AVIs because it's an unsupported hack that can lead to problems, one of which is the audio losing sync when played in Certified DVIX players. I have experienced this first hand with an Avayon Dvix player.

Another reason is that VirtualDubMod, the program that encodes most of the AVIs around, suggests not using it. Straight from the VirtualDubMod FAQs;
http://forum.doom9.org/showthread.php?t=16662

I tried to opened a avi file I get a message "VirtualDub has detected an improper VBR audio encoding in the source AVI file and will rewrite the audio header with standard CBR values during processing for better compatibility.". What does that mean?
It means your AVI contains VBR (variable bitrate) audio, usually mp3. Neither VDub nor AVI supports this, writing it into AVI is a hack that can lead to troubles (namely inconsistent desync and incompressible video frames). If you want to know more about this hack, read the IRC log in the VDubMod FAQ (#14).

Ok, I understood VBR audio is bad, so what do I do when I want to edit AVIs containing VBR audio?
Clean solutions:
Transmux the whole file to a container format supporting vbr audio and edit that (eg Matroska, OGM).
Save AVI with uncompressed audio, do your editing, recompress audio
Demux audio, recompress to cbr mp3, remux, do your editing.

AVI counts on the interleaved audio chunks to be of equal durration and size. That is the only method AVI has of keeping track of time and mantaining propper synch. If the chunks are not of the same size and durration it breaks the AVI specs and leaves you open to all manner of other problems. The audio could lead or lag. It could varry between the two. It could lead to disk thrashing as the software will have to read back and forth in the file trying to get the data it needs totally negating the benefits of AVI(Audio Video Interleave).

And even with this Warning in the FAQs, people STILL insist on using VBR MP3s in AVIs. Please people, what the heck is so special about VBR MP3s that you must continue to go against the Warnings???????

And, if this problem you where having originated from you trying to edit/join the M1Vs before importing them into DVDSP (from your other post), why didn't you just use DVDSP to edit the few frames where the M1Vs join? You can do GOP accurate editing in DVDSP from the Timeline. It would be much better to just let DVDSP do the editing rather than possibly introduce errors by using a different editor. Oh, you might try Extractor for demuxing, I've never had problems with the files it produces.
8)

[DeusExMachina]

OK, well that explains your answer a bit. You see, I am NOT using AVIs, but MPEG source, so I never have any problem with VBR. I almost never use ffmpegX for DiVX encode, so that does not really affect me too much.

Also, I believe you are mistaken about editing in DVDSP, unless these features are well hidden. DVDSP does not even support frame-accurate chapter markers, and does not suport any editing at all, AFAIK. I believe you are thinking about Final Cut. And while could try to re-edit in Final Cut, I do not wish to re-encode, and it seems kind of a lot of effort just to join two KVCD files for archiving. I'll just live with the brief playback glitch as the DVD skips tracks, and minimize it by re-authoring in MyDVDEdit after the build, so I can delete all the unneeded GPRMs assigned by DVDSP and making sure the VTS and VOBs are optimally aligned for playback speed.

*sigh.

[TugBoat]

*sigh*
DVDSP has supported GOP accurate editing since version 2. All you have to do is use the Duration and Clip Start Trim Adjustments. You can use those adjustments on different clips or the same clip over and over for unlimited edits on the same track. It's very easy, and as I said, it allows DVDSP to edit the original clips instead of something that some other editor has messed up.

All you needed to do was to demux the MPGs with Extractor, convert the MP2s with iTunes (then convert the AIFFs to AC3s with Compressor if desired), then drag the M1Vs and AIFFs or AC3s to DVDSP and place them on the same track. From there you would set the Duration, on the first clip, to edit the first clip, or set the Clip Start Trim, on the second clip, to edit the second clip. Very simple and doesn't involve re-encoding or third party editors. Give it a try. Of course, you can use whatever method floats your Boat....
*sigh*