Originally Posted by ticket
On Jaunty, the MP4 file played smoothly, but its smoothness was simply because it was playing the video back in slow motion! However, the audio was racing ahead, so the sound and video were totally out of sync. The same happened when playing in a window and in full screen mode.
On Windows, quicktime played the video flawlessly
Last time I looked, Quicktime always activated the equivalent of -lavdopts skiploopfilter=all:skipframe=nonref (which will allow you to play the video with mplayer on your P4).
The comparison is not completely fair, because imo (and especially for video decoding) the Sempron performs much better than any P4 (even a faster one). You could download a pre-compiled mplayer executable for windows (that is less optimized than would be possible) and I believe it will also succeed playing the videos (at least the H264 sample, I never had frame loss for Apple 720 trailers on a 2GHz Athlon).
I wonder if WMP can use the fact that your screen has a much lower resolution than your sample: For some codecs (not H264 and VC1), this knowledge can be used by MPlayer (lowres) and reduces decoding time by a large factor.
CPU usage in windows would be useful.
PS: No, unfortunately, skiploopfilter and skipframe do not - yet - work for VC1.