To retain maximum quality through to the final DVD from a VHS tape I have been told that one needs to capture from the VHS tape in AVI format at a resolution of 720 X 480 at 29.97 fps 16 bit color video and 48000 16 bit stereo audio. That's "only" about 21MB/second for video information plus the audio information. My system should handle that data flow with ease, dropping no frames at all and with the CPU loafing along at about 30%. But it doesn't. My system is a 1.3MHZ Celeron, Avermedia Philips-based PCI capture card WDM, CMI8738 PCI sound card, Radeon AGP 7000 32MB RAM display card, dedicated 80 GB 7200 RPM IDE HDD UMDA, 350 MB RAM. OS is WinXP Home set as Standard Computer so IRQs could be assigned to devices. Each device has its own IRQ except the Radeon and network cards which share IRQ11. Under ACPI, every device concerned with capturing shared one IRQ -- IRQ5. That the display and netwrok cards still share an IRQ should not be a problems as they are on different buses and I always disconnect from the network when capturing. I use the latest version of Virtual Dub for capturing because I want to have AVI files for later processing. There are just so many neat things you can do to an AVI file while keeping quality top-notch. The problem is that I cannot get clean captures (no dropped frames, no inserted null frames, frame rate at 29.9+/-) at any resolution above 360 X 480. And that is with all processes not essential to the operation of the system shut down. At any resolution greater than 360 X 480 I get unnaceptable levels of inserted null frames, as many as one to one, and frame rate drops to about 12. The status box shows zero dropped frames and the CPU does indeed loaf along at 30% or so. But the resulting capture with all those inserted null frames is useless. The 360 X 480 captures do process into quite good quality 720 X 480 DVDs with spot-on A/V synchronization. But I am frustrated knowing they could be better. Given the abrupt onset of excessive inserted frames and reduction in frame rate I suspect there is a bottleneck somewhere. But I am hanged if I can find out where or how to fix it. I would be delighted to have some sager minds come up with a cause and solution.
Your capture card, and compression (or lack of it) are the bottlenecks. Uncompressed avi needs huge bandwidth, and fast read/write times. Other compressions need less, but can also be slower. mjpeg or huffyuv are your best options, cutting down the need for read/write speed, yet retaining superb quality. The phillips chipset can only process so much video at a given speed as well. Forget 720x480, just use the highest bitrate you can manage, at a smaller framesize, or get a hardware mpeg-2 card.
I capture at 720 X 480 +48k audio with virtual dub using the huffyuv codec. I have no hardware acceleration in the capture card--it's just an S-video input. During capture Virtualdub reports that I'm using just 33% of my processor on my 2.6 Ghz pc. So you might get away with that resolution on your slower machine with huffyuv. Also a large, defragged hard drive is as crucial.
Thank you both, gentlemen, for your responses. I am not capturing uncompressed AVI. I use Hufy and get about 2.5 compression. Are you saying that the Phillips chipset just is not up to the job? My CPU is 1.3GHz. Is that too slow? The drives clearly are not the problem. They benchmark at way over 720x480 16 bit and are rated at 100 MHz/sec, three times what's needed. I have one dedicated 80GB 7000 rpm drive reserved for no other purpose but capturing. So the drive is not the problem. Also, while the CPU is chugging along at 30% +/-, the capture is inserting vast numbers of null frames.
Also, you mention using the highest bitrate you can manage. Is not the bitrate on capture a function of the resolution, frame rate, color depth, etc., and defined by those parameters and also highly variable? Bitrate after capture when convertting the captured file is another matter. You can set the bitrate at a level that will give you a filew of a certian size.
