Just one question for comments by those VCD gurus:

Is there a maximum capture rate for AVI over which no further quality improvements can be achieved? If so, what is this rate, 55, 60, 65, 70 or 75 M/min?

-- Daniel Lee (siangneng@sp.edu.sg), February 01, 2000

Answers

Comments associated with DVD state there is no benifit beyond 9.5Mbits/sec in mpeg2 = about 1.2M/s (1228kb/s or 72M/min).

I quote that because it all depends on the codec, the standard data rate for DV capture in the consumer area is about 3.6M/s (29Mbits/sec, 216M/minute), three times the rate quoted as being acceptable for DVD in mpeg2. It all depends on frame size as well. Analogue capture rates generally needed to be higher before you could not see a difference. These values apply to full frame captures.

If one captures in smaller frame sizes then the data rate required/achieved is smaller. For example a DV full frame capture at 3.6M/s when transfered to a 352x 288 frame usually peaks at about 1.2M/s and after that the whole business is subjective for the produced quality.

The data rate used for VCD's in the mpeg-1 format including the sound component is about 0.17M/s (about 9M/minute) and I do not believe you can compare the formats by data rates alone. The source material needs to have as high a data rate as you can get. Obviously un compressed video is going to be the best but 7M/s for a quarter size picture requires a big hard drive and there is some doubt that you will see any difference at the vcd level anyway.

I find VCD's (352 x 288) based on an avi's with a peak data rate of 1.2M/s very watchable, but then others will say half that rate provides excellent results.

In any event the achieved data rate will relate to whats actually in the picture, and the capture card will not go beyond that which exists. How well it does the job is a different matter, what you get is generally what you pay for, well maybe.......

Certainly, in my view digital source material provides a better end product from its 3.6M/s starting point and at $100US the Pyro 1394 firewire card is a steal.

-- Ross McL (rmclennan@esc.net.au), February 02, 2000.