Sudden increase in dropped frames in mid-capture of VHS?!? W

[JeroenH]

Hey guys,

I have a strange problem on my hands here. First, this is my setup:

HP Vectra
P2@400 (sounds slow but is fast enough)
192 Mb
1x 6 Gb ATA IDE HDD (windows + software)
2x 9.1 Gb UW SCSI HDD's (video data)
BT848 pinnacle capture card
Creative PCI128 sound card
Matrox G200 video card
Adaptec 2940UW SCSI card
VirtualDub 1.4.5
Morgan Multimedia MJPEG codec

Most used settings: video -> size : 384 x 288
frate : 25 fps
color : YUV2
codec : mjpeg @ 85 %
audio -> freq. : 44.1 KHz
8 bit
mono

I've been capturing directly from tv for a while now, and it works mighty fine. Afterwards I canvert to DivX and burn it to CD. Works like a charm. Dropped frames do occur, but only 1 or 2 every 10 mins or so.

But, then I wanted to capture something from a VHS videotape. I didn't have all the right SCART-shit lying around, so I went with the modulated cable signal. I know, I know.... the quality is not too good, but it should work, right? So I first captured a few minutes of tv-signal coming through the VCR to see if it would work. It worked great, no difference with 'normal' capturing. So I started the tape....
I was very suprised to see that I started to drop frames like mad!! When I checked, the 'jitter' and 'disp' values were increasing rapidly, and the framerate wasn't 25.0000 anymore, but was steadily decreasing!!! What the heck is going on here?!? Is my VCR making my capture card think that its framerate should be lower than 25.000 fps? If so, how? And, why? The value started to fluctuate to about 24.97...

Does anyone have *any* idea what this might be? And how it can be solved? I'm at a loss....

Oh yeah, I have all equipment set to PAL here, I heard that that means Picture Always Lovely, well.... not always

Thanx for any help guys,

Jeroen

[JeroenH]

Sorry sorry sorry!!!

My computer hungup while I was posting the first post, and I assumed it wasn't posted.... hence the doublepost.

Again: sorry

Jeroen

[Badalex]

I have the same problem. And the CPU usage is not maximum. I don't get it.

[ironwood321]

Have you tried defragmenting your hard drive? Are you capturing to a hardrive which is seperate from your main system drive? If using win98/95 right click on my computer and in performace change computer type to Network server. Disable Screen Saver and any power down after X minut options. Are you using fast hard disk drives ie UDMA 66 and above? End task evrything except explorer and systray. Remove mdm.exe from your c:\windows directory. Disable Virus Killers and Find Fast in Control pannel.
What capture program are you using? Virtual dub can be ok but is heavy on cpu load try avi_io.

I hope these suggestion help.

[Dman65]

I have heard somewhere of old VHS tapes creating problems with dropped frames and stuff. I am not a video tech wizard so i really can't explain why. It would seem to me that if you see the picture ok it should be capturable. But, like many things in life I guess it isn't as easy as it appears.

Are you defragmenting AND preallocating file space? I have noticed a few times I have gotten dropped frames when the system has to go out and assign new clusters to a file as it grows. I find it much more efficient if I preallocate the file.

[patrickm]

if it always happens in the same section of tape it probably is corruption of the tape. if it captures for 5 minutes, then drops 50 of 60 frames, the frame rate is calculated as an average, not an instantaneous value, so it will decrease, and 24.97 is nothing to worry about, that's around .1% error. the 50 dropped frames could be an issue though.

[FM]

Optimize your computer as shown here:
Win2000 - http://forum.matrox.com/mgaforum/Forum19/HTML/000035.html
Win98 - http://forum.matrox.com/mgaforum/Forum19/HTML/000028.html

You should not have all these problems after that.