virutal dub mod dropping frames but wierd

[lancer]

this is a strange one. until this weekend my machine could capture lossless no problems.

I can capture using virtualdub mod in sync 1.4.9 1.4.10 and 1.4.13.

all of them would capture 720 x 480 no problems, in sync audio, no lost frames.

My machine is

PIII 733
512mb SDRAM
80GB Maxtor to capture
40GB hard drive is my C:\ and the swap file is on there.
Win98 SE
capturing through an Asus 6800 deluxe with video in. capturing using composite
SB live! platinum and capturing audio through the analogue in. no pops or crackles when doing so

I capture with the following

audio at 44khz 16 bit stereo
no overlay (hide on capture set)
video buffers = 10
audio buffers = 36000 as suggested by virtualdub mod in sync readme
crop 108 and 98 from top and bottom as I capture. (having this on or off makes no differnce to this problem)
huffyuv in yuy2 predict median (best)

i've tried video buffers = 36 same problem.

BTW in virtual dub when using the sync mod exe, if you go to timings, I have the first one selected, is this right?

the problem is this. the machine will run, capture fine and lose no frames, when suddenly it drops 12-20 frames in one go. ie my footage will jerk because it's half a seconds to one seconds worth of video lost.

it will do it once and then not do it again for the same time.

but the time it does it is not consistent. it might do it after 6 minutes, after 25, after 29. totally random each time. I've switched off all task bar processes and all other tasks in the background, and capture from a fresh boot into the O/S

things I haven't done, direct draw acceleration both fields. how does this make a difference?

should I up the video buffers more? the more they are, the longer there is before it drops frames. the default is 10, what might I take it too? I've tried 35 and it dropped after 25.16

I am really scratching my head over this one because nothing has been loaded on the machine in weeks and nothing happened different this weekend to any other, and yet suddenly I can't capture lossless.

can anyone suggest some things to try because it is really peeing me off now.

[jggimi]

sounds like background task activity. Virus scanner, or something, may have awakened. Of course, I don't really know. When I capture, nothing is running but Explorer and Vdub -- not even Systray.

I've seen drops due to lousy VHS sources, I suppose because sync is lost.

[lancer]

see I thought that but I checked and there is nothing in the background at all. I close all my taskbar things down, shut off the virus check etc. and I am clean to run.

what has me scratching my head is the fact it is not consistent when it drops the 10-20 frames. there is no apparent reason for it.

BTW video buffers, general configuring of virtual dub mod , any tips

[lemon]

It can be a hard disk issue.
IDE hard disks do something called 'thermal calibration'. I don't know exactly what it is, but, when they get some temperature, they do a recalibration of the heads or something. The result is that every random amount of time, they are some time 'blocked'. It has no effect for normal computer usage, but always causes dropped frames if they do the termal calibration when grabbing video.
You should try playing with the cache settings. Sometimes disabling write cache improves, sometimes making a bigger one improves.
Normally a bigger write cache gives problems, because if when it tries to write the drive is not ready, the cache can get full and not grab some frames until it is empty. If you disable it, you can lose 1-2 frames while you can lose 12-20 with a big cache enabled.

If you can, try another disk, then you'll be sure if it's a disk problem or not.