Does simultaneous computer usage affect capture quality w/USB capture?

[miamicanes]

OK, I had a weak moment seeking instant gratification, and decided to give the ADStech DVDXpress DX2 a shot to see whether it's good enough to keep me happy. So far, it's got one strike against it -- the max bitrate for MPEG-2 seems to be 4,000kbit/sec. Dear god... even in my most aggressive svcd days, the lowest I ever really dared to go was 3,600kbit/sec with suicidally-long GOPs and 2-pass VBR... and in this case, we're talking about on-the-fly encoding with probably no B frames to speak of... . I'm capturing my first tape now, and slightly scared of what it's going to look like...

Anyway, the big question is... with a USB2 capture device, can I freely use the computer for other light tasks with zero risk of dropping frames due to parallel activity? Especially since I have a dual-core A64x2/4200+, 2 gigs, run Windows from a SCSI 15k drive, and I'm capturing to a SATA drive? Intuitively, it seems like the answer should be 'yes' since all the heavy lifting is being done by the DVDXpress DX2, and the computer's own task is comparable to just copying a file from an external USB drive to an internal drive... but it wouldn't shock me in the least if the DVDXpress's designers (and other companies) did something shortsighted and stupid to save 10 cents, like omitting enough of an onboard ram buffer to handle an occasional hiccup at the Windows end lasting for a frame or two...

Actually, while I'm at it... if I ended up taking the DVDXpress back and got a VideoXpress instead (capturing to AVI, which I'm assuming is ultimately DV), could I safely have something like TMPGenc encoding one video while the next is being captured? Or would that be REALLY pushing my luck too much?

Alternatively, if external USB/Firewire DV capture boxes WOULD be affected by simultaneous compression activities on another file, are there any sub-$200 boxes that capture to DV that can write directly to a USB2 or Firewire hard drive THEMSELVES? Perhaps connecting the drive to a PC, writing a config file to it with a special name that the capture box will look for (that among other things, might tell it how to automatically name the files, how long to keep recording once it's started, etc), disconnecting the drive from the PC and connecting it to the capture box, hitting a button on the capture box to initiate capture, and pressing 'play' on the VCR?

[olyteddy]

Get an MPEG2 external like Hauppauge's USB2 PVR if you want to do other stuff and not have to worry about dropped frames.

Edit: didn't notice the card you mention is a hardware encoder. I'd stiil suggest the Hauppauge, though.

[harley2ride]

I have captured tape via firewire on my ads pyro av/link, and done other things (like photo editing), at the same time, and have had no problems. Not sure about your dx2, as I don't know a whole lot about them. I wouldn't recommend encoding one video, while capturing another though. It might work just fine, but I don't like doing things over again, when it isn't really necessary. Just use good common sense when multi-tasking, and don't push the envelope.

[edDV]

USB2 devices are encoding in the box unless working at CIF (webcam) levels. DV and Hauppauge PVR MPeg2 boxes also put little load on the computer. So these can be used while doing something else. Better that you capture to a different drive than the OS in case it or an application hogs the disk.