Dropped frames with USB analog capture devices

Rauld wrote on 3/14/2002, 9:54 PM
Hi Everyone,

When trying to capture, I seem to be dropping tons of frames with my either of my two USB Analog capture devices. They are a Dazzle Digital Video Creator 80 and a Belkin USB Video Bus 2. The USB Bus is sharing an IRQ with the modem and some IRQ steering thing but the modem is never in use while I'm trying to capture. Would anybody have any suggestions for me or is USB analog capture just inherintly (sp?) inferior to other types of input such as a dedicated pci card. I'm dropping a ton of frames. I would hope it's not normal.

Thank you for any advice or words of knowledge,

Raul

My system consists of:

AMD Athlon 800
ASUS A7V motherboard
Via chipset with latest 4 in 1 drivers
512 Megs of 133 SD ram
IBM 30 gig hard drive partitiioned into 3 10gig partitions
NVidia 32 meg video card
EMU APS Sound card

Comments

deef wrote on 3/15/2002, 10:25 AM
Either lower you frame rate via Capture preferences or reduce the resolution on the via the Video menu's dlgs.

You could also try disabling still image support via the Capture preferences and/or disable Square pixels on the View menu. These both take up CPU usage.
Chienworks wrote on 3/15/2002, 3:40 PM
USB (at least USB 1) simply can't transfer data fast enough for a good quality video capture. Analog video comes into the device at 160Mbps (well, not really, since it's analog, but you get the idea) and USB can only transfer 12Mbps. Obviously something's gotta give. Perhaps the Dazzle device you are using does some compression before sending it to the computer, but compressing 14:1 in real time isn't going to give a very good result for a device of that caliber.

I think the best i was able to get out of a USB capture device was 320x240x9 bit at 15fps, and even that dropped frames quite a bit. On the other hand, i tried a $60 WinTV PCI card and could capture 640x480x24 bit at 29.97fps and never drop a frame. The overall quality was still less than wonderful though. Now i'm using an external Analog to DV converter (Sony DVMC-DA2, sadly discontinued) and get delightful results capturing in DV, which only needs about 1/5 the disk space of uncompressed AVI.
Rauld wrote on 3/16/2002, 10:00 AM
Deef,Chienworks,

Thank you for the responses. I should have thought about the bandwith thing before purchasing USB video input. I will try the fixes suggested. Ohterwise I am going to get myself a digital 8 camera or a better analogue capture soloution.

Thanks again,

Raul