Strange problem with dropped frames under VideoWave 4greenspun.com : LUSENET : Video CD : One Thread
I'm having an odd problem capturing video with VideoWave 4. I am trying to capture input from a VCR to an AVI file, but VideoWave keeps dropping about 3% to 5% of my frames. Almost regardless of what resolution and framerate I try to record at, I get roughly the same percentage of dropped frames. I've experimented some, and the only thing I've found that has any effect on the problem is when I record at 10 or fewer FPS, I only drop about 1% of the frames instead of the 3% to 5% I get at all other speeds and resolutions. Also, the loss is not consistent, but rather tends to happen in short bursts. I will go as much as 30 seconds without dropping any frames, and then in the space of 4 or 5 seconds I will drop several frames in quick succession. I am running on a near-top-of-the-line computer, a 1.7 GHz machine with 512 megs of RAM, a relatively new 7200 RPM hard drive, and a GeForce 3 with 64 MB. Anyone have any idea what's going on? I've already tried most of the suggestions at videoguys.com, but they didn't help.
-- Andy Modrovich (email@example.com), May 27, 2002
It pays to have the best analogue source when trying to capture that. Even the fastest, best-tweaked capture device/PC will drop frames with an unstable source. NO, VHS is NOT a stable source. Inexpensive VCRs do not do anything to the sync taken from the running tape: when it disappears, as it is wont to, then for a moment there is no sync output to the TV. The TV usually copes gracefully with this and it takes a massive succession of frames without proper sync from the VCR before glitches, tearing, and rolling appear which may make u think all is well. Merely watching a VHS tape play on TV WILL NOT tell u with any accuracy how stable its sync is. Unfortunately sync is one of those important things a capture device holds dear and even if just one frame had none this is enough to drop the next few, in bursts as u note. For those who will make a living out of capturing analogue video they will invest in, at least, a time-base corrected VCR, use S-VHS, and exclusively the S-video connector. A bit cumbersome, no? It's neither so bad nor so expensive now: the best middle-ground approach is through either a D8 or DV camcorder. You simply dub your VHS tapes to any of these digital formats, then output the DV AVI files to the HDD through FireWire. These formats ARE designed for digitizing and copes very reliably even with poor sources. You only need an inexpensive OHCI FireWire card in your PC, not an expensive analogue capture device. Analogue capture devices only perform to their name when they already are in the $1000 range (or a bit less probably); it is VERY EASY and VERY COMMON to drop at least 1% to %5 of frames anytime. While the latest GeForce 3 & 4 and ATI Radeon 8500 chipset cards can capture analogue video that is not their best suit. The capturing bit is probably only to entice u to buy them. Best they are used for straight display-only purposes.
-- Mehmet Tekdemir (firstname.lastname@example.org), May 28, 2002.
Thanks for your help, that does indeed explain it. Of course, I really don't notice the dropped frames in the AVI; the problem comes in when I try to encode the AVI to MPEG-1. The dropped frames, instead of being "filled in" like they are in the AVI, are simply missing from the finished MPEG, which results in the video and audio tracks falling further and further out of sync as the clip progresses. There ought to be a way to fix that, right? It would certainly be easier and cheaper than buying a bunch of new hardware.
-- Andy Modrovich (email@example.com), May 28, 2002.