Audio Drifting Increasingly Out of Sync
 

I captured a bunch of tapes a while back. Audio was generally 2-5 frames out of sync across the video. Not a huge deal, just a matter of finding a point where a ball bounces or something alone those lines and syncing up.

Now, however, my captures start over a second out of sync and drift from there, meaning the end is two or three seconds out.

I'm not aware of having changed anything in the capture process. What's the likely cause of this?

Any of these can cause sync problems:

capturing to USB hard dives or slow external/internal drives
Running other active applications during capture (word processors, etc.)
Processing/playing another video during capture
Capturing to the operating system's hard drive
Too many PC attachments drawing power from main PC
Hard ddrive defects
Heavy CPU usage problems or overheated CPU
Enabling VirtualDub a/v sync timing management (http://www.digitalfaq.com/forum/vide...html#post45242)
Starting VDub capture with the "F5" key (compatibility audio mode)

There are other causes. How can one list them all? To say that "nothing was changed" is likely not accurate. Something always changes or gets changed.

Always quickly review captures for things like correct sync at begin, middle, and end, at the time of the capture, not 6 months later.
Video and/or audio editors can change audio timing, so I hear. I never had the problem, so can't help with audio edits.

It's a laptop, so AFAIK I have to do one of these two things. I've been capturing to the OS drive (then moving to an external drive, then to my desktop machine to edit). But it worked fine before, so I doubt it's the problem...could it be too full? I've added a lot to it since my first round of captures.

It's none of these.

The first two boxes (dropping and inserting frames) are checked, but none of my captures have reported dropped or inserted frames. 'Do not resync' is checked, 'correct video timing' is checked, 'automatically disable resync' is unchecked, latency is automatic and 30, and the only DirectShow option that's checked is 'force audio clock'.

Hmm. Don't recall whether I started with F5 or F6.

I've posted in this forum and elsewhere that I find audio sync problems baffling because I've never had them, and several efforts to replicate the problem have failed in my case (except for starting a capture with F5, which produced lagging audio). But your remarks reminded me of a forgotten attempt at USB capture with a laptop from many years ago. That was a 15 minute capture that I stopped because I hate trying to work with video on a laptop, which is something no one could pay me do to. In that case audio was out of sync from frame zero.

One factor I didn't mention earlier was monitoring audio during capture. I've tried that with AIW cards and had no problem with it, so I still can't help those who say they had bad sync because they left the audio monitor enabled. There are three precautions I've always taken that are holdovers from my ancient Pentium-3 and Windows 98 days of capture. I turn off internet connections, turn off Windows update, and disable anti-virus. The cards used on various XP PC's were a 7500 AIW and an AIW 9600XT. More recently I use faster PC's these days and have left those factors turned on now and then, but they're still old habits that I fall into often and will set them off sometimes unconsciously. Turning them on still didn't give bad sync.

The only options I turn on in VDub's timing options menu are "sync audio to video by resampling the audio to a faster or slower rate" (which I sometimes turn off anyway just to see what happens, but can detect no difference), and "Audio latency determination" is at "Automatic". No other options are in use in that dialog with AIW cards.

These days, the audio monitor is turned off when I capture with a newer Win7 machine on which I sometimes use a VC500 USB card. The VC500 requires that audio re-sync options should be turned off as well.

Cleaned out the hard drive and tried a capture, and it looks like it's a fraction of a second out the entire way through, which is the result I was initially getting. That one's fairly easy to solve, though.

Okay, looks like I can capture five tapes at a time before my drive gets full enough to start screwing really badly with the sync.

Am I stuck with this limitation, since I'm capping via a laptop? Capturing straight onto the USB drive I'm then shifting my captures to apparently won't help, since USB is a bad idea, and it being a laptop I can't just add another hard drive.