Quantcast Sound speed fluctuations? - digitalFAQ Forum
  #1  
12-03-2019, 06:03 AM
discmeister discmeister is offline
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Hi all,

I've been happily capturing many videos over the past 12 months, using the originally advice gleaned from the experts here.

Recently, though, I've started to have glitches in my raw capture files. Basically the sound slows down in a fraction of a second, then takes anywhere up to half a minute to a) run very slowly for a while, then b) run very quickly until it catches up.

I've attached an MP4 file here so you can see what I mean.

On paper, it would look like there's a bizarre fault with the VHS cassette itself. But when I recapture it, it's fine.

I'm using the same hardware as before - Datavideo TBC-1000 with Panasonic NV-HS950, into VirtualDub via an ATI USB600. I've had no warnings about any hard disk faults or failures. I have experienced the issue using a number of lossless compression algos - mainly Lagarith, which has been my default over the past year, but also UT-Video (I tried it to see if it made any difference).

Could anyone make any suggestions as to what's causing this one? It's driving me nuts.

Regards to all,

Discy


Attached Files
File Type: mp4 Sound fluctuation example.mp4 (19.26 MB, 2 downloads)
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  #2  
12-03-2019, 09:45 AM
keaton keaton is offline
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If you don't see/hear the issue while playing the tape to a monitor/tv or in preview mode in Virtualdub without capturing, then it would sure seem to be something happening during capture itself. Some have not had issue capturing with Lagarith, although the general advice I've gathered from this forum is to capture with Huffyuv. The reason being it is less CPU intensive and causes less real time issues. Although, if there were some issue with the hard drive, I guess it wouldn't matter what codec you captured with. You can convert to Lagarith after capture in Virtualdub/Avisynth if you prefer to work with that. Huffyuv is captured with 4:2:2 color space, converting to Lagarith changes to 4:2:0 colorspace.

I hope your problem is that simple. I didn't watch the video, but the symptoms you describe sure don't sound like something an analog piece of equipment would do, unless you had a serious tape or player issue. Sync issues usually are a "slow creep" with dropped frames, not a drastic event like you describe. That sounds more like something in the digital realm on your computer. Virtualdub shows metrics during capture. You may not have that enabled, but it should be enabled/disabled from menu options. I see metrics in the very bottom of the window, and also on the right hand side metrics pane. If you have an audio or video issue, you should see changes for the audio or video stats suggesting it has lost sync and is trying to recover (if you've configured virtualdub to do so, see Capturing with VirtualDub [Settings Guide]). Although, I wouldn't expect that to happen so suddenly when you have a TBC-1000 in the path. It should be really good about keeping video going at a steady rate with the audio, even if there were a tape glitch. But if the codec cannot keep up with real time capture, or some weird hard drive glitch, then I would expect to see a drastic change in the metrics.

One other thought is there is some process or service running on your computer that occasionally takes too much processor away and causes this digital hiccup during capture. It is important to have as little going on as possible on your computer during capture. Windows is not a real time operating system, so the best way to ensure something real time like video capture is not disturbed is to have it do nothing else. Depending on which version of Windows you have, this may be more difficult to guarantee, as Windows gets more bloated with processes and services with each generation. I use XP offline and am fine. I cannot speak to what could be done if it's later version of Windows. Best I can say is go into Task Manager and disable/kill as much as you can. Some knowledge of windows may be needed. Certainly disconnect from a network to avoid outside interruptions.

Last edited by keaton; 12-03-2019 at 10:30 AM.
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  #3  
12-03-2019, 10:28 AM
msgohan msgohan is offline
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I agree that this seems like VirtualDub's Resync option in action.

Quote:
Originally Posted by keaton View Post
Huffyuv is captured with 4:2:2 color space, converting to Lagarith changes to 4:2:0 colorspace.
Lagarith actually supports both.
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  #4  
12-04-2019, 04:22 AM
discmeister discmeister is offline
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Thanks for your responses. So if it is VirtualDub's resync feature in operation, what would that suggest? A fault with my TBC? Could it, for example, be down to overheating?

Incidentally, I switched to Lagarith from HuffyYUV because I found occasional sound glitches when I imported the file into Premiere Pro. Although you make a fair point that I could use it for capture and then convert to Lagarith as I do my post-processing in VirtualDub/AVISynth before eventual import into a NLE.

All comments/suggestions gratefully received. I've decided to pause what is a very major series of conversions until I get to the bottom of this.

Discy
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  #5  
12-04-2019, 10:12 AM
msgohan msgohan is offline
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Try capturing with these timing options: Drops and Inserts turned on and set to Do not resync. I never turn on the Resync option. Sanlyn does.

I think interruptions caused by CPU/HDD can cause this effect with Resync on, but it's been a long time since I've tested the options. Normally momentary CPU/HDD issues would cause drops/inserts.
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  #6  
12-04-2019, 10:15 AM
discmeister discmeister is offline
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Thanks. I'll give that a try.
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