Virtualdub VCR capture no dropped frames but 5400 inserted frames in 1 hour

[suloku]

Hi, I'm having a problem with capturing with virtualdub, which I think is preaty strange also (as I lack the knowledge about why this happens):

If I capture from composite input trough a VCR with overlay ON cpu goes over 100% (actually none of the cores goes higher than 90%, so I think it's ok), there are no dropped frames but the inserted frames go up to 5400 in one hour. The average rate for video is 23.58 fps and I'm capturing at 25 fps. The resulting video plays fine as long as I can tell.

If I capture with overlay off cpu usage disminishes and there are no dropped frames and very few inserted frames (200-400, I don't remember now, but the vhs has several cuts, so it might be for that reason). The average rate for video is 24.9 or so, which I think is very good, considering I'm capturing at 25 fps. The problem is that when doing this the audio gets off sync, it finishes about 3 minutes earlier than the video.

I have disabled resync in the timing... tab, as I'm capturing video and audio trough the same card, so this sync problem is driving me crazy.

Are 5400 inserted frames in 1 hour acceptable?
Why is audio unsync when disabling overlay?

Those are my questions, thank you very much

[jagabo]

5400 inserted frames in an hour is unacceptable. That's 1 frame in every 20.

I would start by capturing something cleaner than VHS. Like a DVD player (playing a non-CSS DVD) or cable TV box. Get that working perfectly, then look at VHS.

[suloku]

Thanks for replying, as I thought that number of inserted frames is too large (even though I think it's unnoticeable for the human eye), I guess it's related to the video stream being captured at an average of 23.6 fps when the capture is 25 fps, hence the inserted frames to compensate. What would be a tolerable rate of inserted frames?

As I said, disabling video overlay in virtualdub rises the average bitrate to nearly 25 fps, which causes only a 0.007% of inserted frames (having overlay causes a 0.05% of inserted frames), the problem is that by doing this audio is unsynched in the resulting avi file, as much as ending 3 minutes earlier in a 1hour 2 minutes capture, which I think is an abnormaly large unsynch, and I don't know what causes this.

[hech54]

resulting avi file

What kind of "avi file"?

[jagabo]

Thanks for replying, as I thought that number of inserted frames is too large (even though I think it's unnoticeable for the human eye),

Actually, it should be noticeable. With an inserted frame every 20 frames or so just about every panning shot will have a little jerk. Most smooth motions will also have a similar jerk.

What would be a tolerable rate of inserted frames?

It depends on the video. If there's very little motion you may not notice missing or duplicate frames. If there are a lot of smooth motions you will see little jerks every now and then. It also depends on the nature of the errors. A lot in a row may be more noticeable than when they are spread out. And a lot depends on your personal taste.

As I said, disabling video overlay in virtualdub rises the average bitrate to nearly 25 fps, which causes only a 0.007% of inserted frames (having overlay causes a 0.05% of inserted frames),

That's a tolerable amount for most material.

the problem is that by doing this audio is unsynched in the resulting avi file, as much as ending 3 minutes earlier in a 1hour 2 minutes capture, which I think is an abnormaly large unsynch, and I don't know what causes this.

I don't now either. Is the audio in sync at the start and slowly drifts out of sync? Or get worse in steps? Or is it off by the same amount all the way through? The first and last are easy to fix.

[suloku]

I'm encoding with mpeg-4 and divx one-pass - quality at 100%. I'm also applying the deinterlace - area based 1.4 filer with "blend insetead of interpolate" option disabled. I know it is a demmanding compression, but as I said none of the cores goes higher than 90%, being the most used core at 60-80% most of the time.

But summing up, with the very same settings:

-Overlay ON: capture average frame rate 23,6 fps, audio in sync
-Overlay OFF: capture average frame rate 24,8, audio not in sync.

This is what I don't understand, overlay off should give more cpu to virtualdub (and it does, as fps rate goes up and inserts goe down) but it gets the audio unsynched

Here's a screen of my latest try to capture the vhs (btw, I have audio set to mono, uncompressed, 16 bit 48Khz)

[jagabo]

Open one of your caps in VirtualDub, find a sequence with smooth, moderate motion, and step through frame by frame. Do you see any obvious repeat frames or skipped frames?

In my experience capturing with Divx is guaranteed to give A/V sync problems. Try switching to HuffYUV (the files will be very large of course) for a test and see if the situation improves. What happens if you capture without audio? Do you still get dropped/inserted frames? You're not compressing the audio while capturing are you? That's another common cause of problems.

Less than 100 percent CPU usage is no guarantee of trouble free captures. With realtime processes not only do you have to have enough CPU power to perform the job but that power must be available at the right time. As a simple example, say your computer could capture 60 fps for half a second, then locked up for half a second, repeatedly. On average you have enough CPU power to capture 30 fps. But when capturing 30 fps video those lockups mean you will drop half the frames every second. Ie, during those half second intervals new frames of video keep arriving from the capture card but the CPU is unavailable to process them, so they are lost.

There's always the sticky about capturing problems if you haven't seen it already:
https://forum.videohelp.com/threads/104098-Why-does-your-system-drop-frames

[hech54]

capturing with Divx is guaranteed to give A/V sync problems.

Exactly. People often complain about how long it takes to convert/compress stuff to Xvix/Divx, but expect to capture as Xvid/Divx.....downright silly idea.

[jagabo]

Divx at its fastest setting (forget what it's called, but the free version doesn't have it, no b-frames, little or no motion search) is almost as fast as HuffYUV and PicVideo MJPEG. Of course, it doesn't compress as well at that setting. Still, it seems to have problems with video capture, especially at the very start (probably some initialization issue), then sporadically during capture.

[suloku]

I don't now either. Is the audio in sync at the start and slowly drifts out of sync? Or get worse in steps? Or is it off by the same amount all the way through? The first and last are easy to fix.

It starts somewhat synched, but gets noticeable in the first minutes until the 3 minutes unsynch after 1 hour.

Open one of your caps in VirtualDub, find a sequence with smooth, moderate motion, and step through frame by frame. Do you see any obvious repeat frames or skipped frames?

In the capture with overlay ON there are 1-2 inserted frames (I haven't seen more than 2 in a row, but the most common is 2 inserted frames). They occur frequently, but not within the same second, and as there are mostly 2 inserted frames in a row it would mean that the inserction would be "noticeable"every 2 seconds on average (rough calculations of course). I guess this is why the captured video seems to play fine.

By the way I don't have any problem with drops, in the image i posted you can see 14 drops, but as I said the vhs has several cuts and a scene at the last part that has some distortion, which may contribute to those drops, but I think 14 drops in 1 hour is more than enough.

It stills puzzles me what has the overlay option to do with the audio being unsyched when the video is actually better.


I'll try to capture with other codecs and see if the unsynch occurs, I didn't know divx was so bad for capturing, as audio and video are captured toguether and my computer seems to be able to handle it.

I'll also try the latest version of virtualdub (I'm with 1.9.9)


EDIT: I'm an idiot. In the screen I posted I can clearly see that average audio rate is 44915 while it should be 48000 (or similar).

I've tried virtualdub 1.10 with the same settings, everything seems to be working alright now (I just tested 6 minutes) but video and audio rates where constantly the wanted ones, so I guess 1.9.9 had some kind of bug.

I'll tell you if the full capture went OK

[jagabo]

I forgot to ask about the odd audio sample rate. Sounds like things are working now...

[suloku]

I forgot to ask about the odd audio sample rate. Sounds like things are working now...

False alarm, after 20 minutes capturing audio sample rate went down to 43000. I'm gonna try another encoder.

Maybe capturing audio at 44.10 will give better results? It really might be my computer not being powerful enough to encode divx on the fly, but I'm not using audio compression, so why does the audio sample rate go down when I swith off overlay?

Anyway I captured in dv with very good results (less than 200 inserted frames, only 12 dropped frames, many may be in the last minute, as I'm using the stop conditions tab with 2 minutes marging for recording).
I freed some space and I'm gonna go with HuffYUV, as I'll need to reenconde the movie anyways. I thought it would take more space, but it only takes 30 gigs per hour and the tapes I need to capture are 1 hour or 2 hour length.

[Brad]

VirtualDub has a few options that affect audio in order to keep things in sync when the video stream isn't keeping up.