so it would appear that the only values that actually work are 0.0, 0.5, 1.0, and 2.0...
i tried setting it to 0.25 since I want it to play at 1/4th of the natural speed, but it played it at 1/2 of the natural speed instead. can anyone confirm this?
Confirmed. I actually had a ticket with Apple DTS open for this issue and a bug filed. The only supported values are 0.50, 0.67, 0.80, 1.0, 1.25, 1.50, and 2.0. All other settings are rounded to nearest value.