Audio sync drift during capture

[mdailor]

Hi,

I am having a problem with audio/video sync during capture. I am using ATI's MMC 7.1 with a TV Wonder card to capture to an AVI file with the HuffYUV compressor on a fresh install of Windows 2000. The captured AVI file starts off with the audio and video in sync, but the sync progressively drifts apart throughout the file. I am using this exact same setup on a Win 98 machine with a 550MHz Athalon processor and it works great (aside from a 225ms constant sync difference that TEMPGenc's "Audio Gap" setting takes care of), but on the Win 2000 machine with a 988MHz processor I can't seem to nail it. Any suggestions? I don't want to fix the captured files, what I really want to capture them in sync in the first place. Thanx in advance!

System is:
Gateway Pentium 988MHz
256 MB RAM
Windows 2000
DirectX 8.1
ATI TV Wonder
ATI MMC 7.1
HuffYUV 2.1.1

[Sulik]

Either:
1. Use MMC 7.5
2. Upgrade your sound card
3. Change your motherboard

[DaMo]

TEMPGenc's "Audio Gap" setting? Where the hell is that?

[mdailor]

Either:
1. Use MMC 7.5
2. Upgrade your sound card
3. Change your motherboard

Oh, I see. So basically I just start swapping hardware and software in an out until I stumble across something that works? Gee thanks, but I think I could've done that on my own. Can anyone else shed some light on what causes this type of behaviour and what they've done to solve their problem?

[mdailor]

TEMPGenc's "Audio Gap" setting? Where the hell is that?

Backgrounder:
Most sound cards have some amount of latency. i.e., there is a small delay between you sending sound into it and the actual playing of the sound. It's not that noticeable with dialog, but it you make music or music videos with your computer (which I do) it can be a show stopper. Latencey is a constant value. In my case, it takes 225 ms. for the sound that I feed into the card to appear at the outputs. So when I capture audio+video, the audio always lags behind the video by 225 ms. Note that this is a CONSTANT delay as opposed to a VARIABLE delay (where the audio is increasingly behind or ahead of the video throughout the file).

So:
If you have a captured file with a constant audio delay, TEMPGenc gives you a way to easily correct it using the Audiao Gap setting.

o Start TEMPGenc
o Click the Settings button
o Click the Advanced tab
o Double click on Source Range
o In the Audio Gap Correct box, type in the latency value. For me, this is 225. You'll need to do a little trial and error to determine the value for your own card by encoding a small section of the same video several times while increasing/decreasing the latency value until the sound and picture line up. Once you've nailed it, write it down and use it for all your encodes.

[Mirror_Image]

Try this "time stretch" thing for starters:

http://www.vcdhelp.com/phpBB/viewtopic.php?t=78944

I always have the same sort of trouble with cable-TV captured DivX movies, but I don't convert them to mpeg, so this might not apply:

I open the avi in virtualdub. If all I'm doing is fixing a gradual sync problem, I set both audio and video to Direct Stream Copy. I go to video - frame rate - change so audio and video match, and use the value that vdub has figured automatically (note this will raise your frame rate slightly, which you may not want if later converting to VCD standard mpeg). I then go to audio - audio interleave - change the interleave to every 30 frames.

Save as a new AVI, then play it and see if the gradual sync problem is still there. If it still exists, do everything the same except increase the frame rate 0.001 fps until it syncs adequately. Offset the sound to get it synced at the start if necessary, but change the frame rate to fix it if it is good at the start but then desyncs as the movie plays.

TEMPGenc's "Audio Gap" setting? Where the hell is that?

Click the "Settings" button that is on the main screen (settings, load, save), and then click the advanced tab, then double click "Source Range" and there it is.

[Chuck2002]

Go find a copy of SoundForge VideoFactory 2.0 or VideoVegas 3.0 and your troubles will be cured. Sometimes all the free programs available don't do the job. Was having all kind of sync problems and after switching have had none. Have you not noticed that people with the snyc problems are all using free software. Sometimes the small price is worth the expense.

[mdailor]

Mirror_Image:
I appreciate the reply, but you're right, I *am* making VCD-compliant files and so changing the frame rate is going to skewer me. What I'd really like to do, though, is prevent the drift from happening in the first place rather than massaging the AVI file. I'm capturing and encoding about 12 hours of video a day, and I'd have to build myself a server farm to handle the throughput! :^)

Chuck2002: I actually *do* have a VideoFactory 2.0, and it didn't do the job for me on Win98. In fact, they (VF support) told me to use VF to capture my videos, TEMPGenc to encode them, and back to VF to burn them! But I haven't tried it on Win 2000, think I will do that next. 'Cause it's eating me up that it's collecting expensive dust on my shelf. :^) Thanks.

[Sulik]

Either your sound card has a bad clock accuracy or the VIA chipset is causing the drift (not enough bandwidth on the pci bus) -> I had the same problem on my P3-700with VIA KT133.
If you capture with MMC 7.1 you may get a drift that may or may not correct itself with time (usually will get gradually worse).
MMC 7.5 handles this much better -> I never had any sync issues on that system after upgrading to MMC 7.5.

[markh]

I have had sync problems on my machine in the past. I have one of the ATI wonder PCI cards.

It does appear to be something specific to my SB Live Value card, but I fixed it for the most part by simply uninstalling sound/ATI drivers and reinstalling.

Sometimes you can install an application that you think should have no effect but it DOES. For instance I installed Morpheus and Limewire. The former has its own little theatre app, and I think it screwed the pooch. I started getting dropped packets and sync issues. The reinstall fixed.

BTW, to this day I _still_ have sync issues with Womble, an editor that most have no problems with.

mark