Problem with dropped frames

[iKlEiTlH]

Does anyone know what factors affect the rate of dropped frames?
I use an ATI AIW RADEON and recently experimented with capturing to Divx using VirtualDub, and can't seem to capture without dropping frames.
It's strange, because I'll capture using the same setting, but it often results in a different rate of dropped frames.
I know that it's possible to start dropping frames when capturing at high bitrates, but even when choosing a low bitrate (600), I still end up dropping frames.
It shouldn't be my computer slowing things down either, because I usually defrag before capturing, and I'm running a 1ghz duron processor.
What's causing VirtualDub to drop frames while I'm capturing?

[Anonymous65]

I have found that with the same capture settings, some times I will drop frames, and sometimes I will not. To "fix" the problems when dropping frames, I stop and restart the capture. Other times I have to reboot the PC to make it stop dropping frames. I guess it's an operating system and software instability issue.

SK

[CubDukat]

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On 2001-08-08 21:15:04, iKlEiTlH wrote:
Does anyone know what factors affect the rate of dropped frames?
I use an ATI AIW RADEON and recently experimented with capturing to Divx using VirtualDub, and can't seem to capture without dropping frames.
It's strange, because I'll capture using the same setting, but it often results in a different rate of dropped frames.
I know that it's possible to start dropping frames when capturing at high bitrates, but even when choosing a low bitrate (600), I still end up dropping frames.
It shouldn't be my computer slowing things down either, because I usually defrag before capturing, and I'm running a 1ghz duron processor.
What's causing VirtualDub to drop frames while I'm capturing?

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I had similar problems with capturing directly to DivX, then I remembered reading somewhere that the Angelpotion codec is completely unsuitable for direct captures, but rather should be used exclusively for post-capture encoding and playback. Even with a 1GHz Duron, it still takes up a lot of the CPU's time because even though it's almost as fast as a corresponding full Athlon, it's still a slightly hobbled chip--just less so than the Celeron is compared to the P3.

The short answer is, AFAIK, the Angelpotion codec is not meant for direct capturing. I suppose if you play around with it, you could find the balance between quality and dropped frames, but who wants to work that hard?

[sdmig]

Make sure that you have (no Recompression) selected in the Recompression dialog box. If you have DivX or any other codec in the list you will always get dropped frames.

'mig

[Dman65]

Which DivX CODEC are you using?

What resolution are you capturing at?

How many frames are you losing?

I capture 320*240 using a Pentium III 500mhz and the Microsoft MPEG4V2 CODEC that is an older version before they locked out its use in AVIs and while the capture program does report lost frames, it is about 1 every 20-30 seconds and in the grand scheme of things isn't really noticeable in the final product and probably has as much to do with synching the video to the sound card as anything else.

Are the dropped frames noticeable in the final product? To me that is the item of importance. If you drop .5% of your frames I doubt that you are going to even notice it unless they are all dropping at one time in which case you are probably dealing with a fragmented hard drive.

I tried for about half an hour once to try to capture 640x480 MPEG4 real time. Hahahahaha, it was funny anyhow. Lost 90% of the frames.

[iKlEiTlH]

I'm using the DivX MPEG-4 Video Codec v3.2 by Kristal Studios.
I capture at 320x240, and the rate of frames dropped seems to be totally random.
Sometimes I drop few to no frames during a couple of minutes of capture, but other times it drops a lot.
What's an acceptable rate of dropped frames?
Is it even possible to capture 1-2 hours worth of video from VHS tapes without dropping a single frame?
Even during my best capture sessions, I have yet to be 100% successful in keeping all my frames from dropping.
I also noticed that restarting VirtualDub does help on occaision as well.
Another question: would it be better to capture first using PICVIDEO MJPEG or HUFFYUV and then encode it as a DivX afterwards, or should I just capture straight into a DivX?

[Dman65]

I think most people would say you would get a better capture using Huffy or MJPEG and then encoding that if your system is fast enough to capture that without a lot of loss.

There are a lot of factors that affect frame loss.

If you are getting lots of lost frames all the time your hardware is most likely unable to keep up.

If you get a block of lost frames every once in a while, but everything works fine otherwise, you probably have a fragmented hard drive.

If you get one frame lost that happens at a fairly usual frequency, it is more than likely the system dropping a frame to synch the video to your sound card.

Have you watched your captures? Do they look jerky? If they look ok, then your capture is okay in my opinion. I record video to play it back and watch it later rather than to figure out if it had frames dropped in it. If it looks ok to my eye, then it is okay.

[circleking]

Also, I am using the ATI AIW Radeon AGP to capture. I have Athlon 950Mhz. I use VirtualDub with PICVideo MJPEG codec (640x480 resolution). I have Monster sound card.

I get 1 dropped frame for approx. every 2500 frames (very regularly). This is acceptable except if the capture runs for 25 minutes or so (long enough to lose 20 or more frames). Then I start to lose audio sync.

BTW I lose the same amount of frames at 480x480 and 720x480, and no matter what quality PICVideo codec is set for (I usually set for 18). I also tried changing video buffer settings in VirtualDub with no positive change.

Someone mentioned that dropped frames are caused by sync to sound card. If that were so I shouldn't lose sync, eh?

Anyone know what's up with this yet?

(edited to get rid of smiley I didn't want)

<font size=-1>[ This Message was edited by: circleking on 2001-08-14 22:13:26 ]</font>

[EP10]

Pointers:

• Make sure that if your HD support's it to check DMA.
• Check if card shares IRQ's.
• Possibly disable Overlay while capturing.
• Use a second HD only for capturing.
• Use a clean system.
• Optionaly disable "Write behind caching"
• Use latest ActiveX (=version
• Make sure latest drivers for Videocard are installed
• Maybe try "reference" drivers for videocard***

*** These drivers generaly are more up to date the the ones from the card-company. For example Riva TNT(2) drivers. Check your card's chipset and look for it.

[EP10]

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Use latest ActiveX (=version
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is in this case wrongly translated as a smiley, but should read 8 & )
So version Eight

[circleking]

Thanks for all the help.

Just for everyone's information. I solved my problem of regular frame dropping by altering the capture frame rate to the average frame rate reported in VirtualDub during a capture.

BTW this was mentioned in the 'tips' section of VirtualDub's help tab. (I guess it pays to read that stuff eh.)

Procedure: Make a capture long enough for the average frame rate to become stable in VirtualDub. Stop the capture. Then set the frame rate in capture settings to that value. (Mine was 29.965 NTSC) This also dropped my CPU usage from around 30% to around 15%.

This may not help everyone's problem, but if you keep dropping a frame at a regular interval, you might try this fix.

[zzyzzx]

I get tons of dropped frames when using Virtualdub, but not with other capture programs. I have no idea why. I don't see how anyone could be using Virtualdub for capture.