What fraction of work is iDCT?

[Jeffrey W. Baker]

I am unfamiliar with the workload needed to decode a DVD.  Can someone
please characterize for me how frequently the iDCT need to be performed,
and what fraction of the CPU load it normally represents?  I have an iDCT
routine for AltiVec to replace the broken routine currently in the source
tree.  This routine performs the transform at the rate of 377000
transforms per second on an otheriwse idle 400 MHz 7410.  With the
"classic" iDCT, the machine drops about every fifth frame.  How much
should I expect this new routine to boost performance?

I'll plug the routine in tomorrow and have some emperical data.

Regards,
Jeffrey