Quantcast Frame drop every 100 seconds exactly - digitalFAQ Forum
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03-22-2006, 02:29 AM
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Hey Kevin, I've got a situation I'd like to run by you and my fellow LordSmurf fans. Sorry for the epic post, but more info is better than not enough, right?

For the past 3 years, I've been capturing AVI through an ATI AIW 128 PCI 16MB, using VirtualDub Sync Mod and HuffYUV. Once I found the sync mod, I have never had a problem with dropped frames. The downside was that I had to configure my machine as a dual-boot, with the C drive as a WinME partition dedicated to capturing only. I was capturing to a separate FAT32 partition on another physical drive. I do all my processing/encoding in WinXP, so the dual-boot was a cumbersome but necessary solution to the lack of good drivers for that card in WinXP. When capping, the CPU load was generally 75-95%, but I didn't drop any frames in the 2hr5min VHS capture interval...and some of the source tapes are pretty ratty. I usually engage the line TBC in my JVC SRV10-U vcr, or I try my AVT8710 full-frame TBC in more challenging scenarios.

Recently, I bought a used AIW Radeon 7500 AGP, and decided to get my capture rig running in WinXP. After imaging the old config, I wiped everything and did a clean install. Now, my old nemesis - dropped frames, has reared its ugly head. I've been working through the list of "usual suspects" to iron out the problem. Currently, I have my system drive (IBM 40GB) as master on primary IDE bus, my capture drive (WD 300GB) as slave on same (another HD and a DVD burner are on secondary IDE). Both are formatted NTFS and the capture drive is empty. According to HDtach, my capture drive is my fastest drive. DMA is enabled on both and they report UDMA 5 status. The machine is a 1.5G P4 on an Intel motherboard, 400MHz front-side bus and 256MB rambus memory. The sound card is a Creative EQ1371 (non-Audigy). I have shut down all non-essential background tasks, and pared my services down using the guides compiled by "Black Viper" and by pcaudiolabs.com, and some common sense. I even created a hardware profile, where I disable all non-essential hardware like network card, USB card, firewire card, comm ports and parallel port. I have tried to eliminate as many variables as possible.

So, I've tried many capture apps in my quest to get a clean capture. VirtualDub, using the xp sp2 vfw wrapper, reports between 47-50% CPU usage during capture but drops a single frame at exactly 100 second intervals. This value seems significant, as it is 2997 frames between drops, and NTSC is 29.97 frames per second. But with the sync mod, I was able to overcome the clock mismatch between video and audio cards in my old configuration. Here is a table of the dropped frames:

Frame # TimeFrame diff Time diff
298999.734&n bsp;299099.734

5986 199.73529971 00.001
8983 299.73629971 00.001
11980 399.73729971 00.001
14977 499.73829971 00.001
17974 599.73829971 00.000
20971 699.73929971 00.001
23968 799.74029971 00.001
26965 899.74129971 00.001

Before paring down my system as detailed above, I ran some WDM-based capture programs. VirtualVCR dropped many frames. iuVCR (registered) won't let me select any resolution above VCD values. My biggest success so far is with AMCap, which lets me capture D1 resolution without dropping frames over an ~12min interval. Problem with that is that I can't use the compression I want, I have to capture at 720x480 when I know the card is 704 native, and I haven't figured out how to get 48kHz audio yet (I'd rather not upsample 44.1kHz) ATI MMC 9.02 drops frames as well, and I didn't get a readout of frame drops during capture as shown in the digitalfaq capture guide. I intend to go back tonight and check what kind of response I get to capturing in my pared-down hardware profile with the above software, to see if the dropped frame pattern is independent of the capture program.

-Does any of the above raise any flags as far as blatant configuration problems, and do you have any recommendations regarding the best drivers/capture program for my new-to-me card? Currently, I'm running the 6.14.10.6246 driver.

-In my BIOS, which AGP aperature should I use, 64MB or 256MB. Is that 1x & 4x, since I have 64mb onboard the ATI card?

-Any ideas about the significance of a periodic frame drop every 100 seconds?

Thanks for your time and attention!
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  #2  
04-13-2006, 05:12 AM
awow69 awow69 is offline
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Okay, I'll answer my own question...

The solution that I eventually hit upon was to change the capture framerate in VirtualDub. I've always heard that in order to get 29.970, you had to have VD set at 29.9697 because of some internal VD issue. Changing this value to 29.9706 has eliminated the problem. Glad I found the fix while I still had some hair left.
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04-13-2006, 08:31 PM
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I am so sorry this post slipped by me. If that ever happens again, and I do not reply within 2-3 days, send an e-mail from the main page of digitalFAQ.com and let me know I've missed a question. The Internet is not as perfect as some believe, sites make mistakes (like not sending e-mail notification of a new post!).

However, I would have never guessed that as being the fix, we would have been testing other audio cards or using other capture software or codecs.

I would also have suggested you not use VirtualDub for capture, but rather ATI MMC, following the guides. I would further have suggested that, had HuffYUV been a problem, to try another codec (MJPEG or Alparysoft) or simply go uncompressed.

For some more advanced information on what AGP aperture is, read this: http://www.techpowerup.com/articles/...ing/vidcard/43. Basically, set it at 256MB, but it's really nothing more than a safety net. It does not mean you'll use it, but it's there if needed.

The significance of a dropped frame on occasion, depending on where it falls can go either unnoticed or it can be a huge video blemish. If you're panning a raceway, it'll be a problem. If you're timelapsing the growth of a flower, nobody will notice. In general, you'll want to avoid them.

I've never heard that rumor on VirtualDub needing a lower custom framerate. That is either before my time (I missed the first couple years worth of VirtualDub, or it was just a bad rumor that I never saw. In general, something like that should never be true. Most often, something like that is a defect in the card or software, in which case I'd never use it. You should always be able to capture the true framerate, like 29.970.

Anyway, glad you figured it out.


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04-14-2006, 08:15 AM
awow69 awow69 is offline
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What I had in my favor was the knowledge that this hardware and software could be configured to capture without dropped frames. I just had to figure out how to do it again in XP. My next step would have been to try different versions of the ATI drivers...my AIW128 only worked well with an older version, not the latest one for that card.

I would love to get MMC working, but it just might have too much overhead for my particular hardware config. Strange that I don't get a display of dropped frames like in the guide...only # of frames captured is displayed. For whatever reason, all my attempts at WDM-based capture have failed to yield satisfactory results - always dropped frames. I think I tried every available program, and I had to revert to VFW-based VDub.

Regarding VDub framerate, it's no rumor. You can't dial in exactly 29.970. That's the only aspect of this great program that seems inherently flawed, but it doesn't significantly affect the result. I always add the assumeFPS(29.970) line in my AVIsynth scripts, and the change in run time on a 2 hour capture is on the order of milliseconds. Because I am focused currently on concert footage shot from the audience, I always resync the audio with a better version, so I can either alter the audio to match the new video runtime, or just fix it during the resync process.

Thanks for the link regarding AGP aperature! Cheers...
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