I have absolutely no idea what a SAM and OS4 are capable of (as a die-hard classic user) but for smooth DVD playback you need
- DMA transfer for the DVD drive (PIO will heavily load the CPU)
- (hardware) video overlay on the gfx card
-- MPEG-2 uses YCbCr color space (similar to YUV); using the CPU for RGB conversion costs quite a bit of power
-- scaling the image to the desired size - again - puts load on the CPU
Remember, you've got 40 ms to decode and show each video frame (PAL). If you waste too much for data transfer, color space conversion and scaling you're quickly running out of time.
