DCT observations
I recall that when I was developing the DCT code I ran it through AMD's CodeAnalyst (then in beta form). My DCT did a lot of its work in floating point on normal 8x8 macroblocks. MMX was used a lot too - I did all I could to make it fast but above all accurate.
The CodeAnalyst pipelining graph was amazing. The CPU was completely stalled by full pipelines. No memory nor decoder bottleneck , just instruction after instruction waiting for pipeline stages to retire. I managed to keep everything in registers and did some tricky bits but in the end there just wasn't much more that could be done. There was a lot of MMX too with PAVG used heavily for motion comp.
It was nearly an optimal DCT output-quality wise.
I don't know about XviD but the DivX encoder on an XP 1800+, without any external hardware, was faster than realtime too. I think the results of software are about the same. In that scenario the cost of the video disappears.
Still I stand by my belief that video processing is one, if not THE, app that will drive home users to needing faster hardware. Funny thing is that its a different demographic interested in processing video - and older group, some retired, who have the money to spend.
Cheers
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