I'm running Windows XP SP2 on an AMD Athlon XP Barton 2500+ at 2800+ with 1gig Kingston PC400 in dual channel, an ATI Radeon X800XT 256meg AGP 8x (Catalyst 5.9) on an nForce2 system (latest chipset drivers), and I have trouble decoding H.264 at 480p (in fullscreen) or better. At 480p it works alright, but chops up every now and then, and just after watching a video at 640x480 (displayed in fullscreen) it started getting super choppy, even with QuicktimePlayer.exe at high priority.

An example are the TWIT IPTV shows. My computer can barely keep up in fullscreen.

I can only dream of watching 720p or 1080p trailers on Apple's trailer site.

The annoying part is with my ATI X800XT, I can watch Windows Media 9 HD streams at 1080p flawlessly in fullscreen. Thanks to DxVA. Why can't Apple take advantage of hardware acceleration in X86..?

Also, in higher action videos with Quicktime 7 H.264 I notice alot of tearing. Is this common? Am I alone?

Just for the hell of it, I'm also running the videos from my Western Digital Raptor 36gig SATA 10,000RPM drive.

This does not answer your question, but maybe you could try decoding with Nero media player or FFDShow.

I did try opening the video in WMP10 with ffdshow H.264, and a frame of the video will display, and I can skip around an other frames will show, but the video/audio will not play. Also, the video is noticably blurrier. I might need to tweak ffdshow settings.

I will try a newer build of the H.264 (x264) codec from here: http://mirror01.x264.nl/x264/ later.

Thanks..

Also a note.. can the ffdshow and nero versions play the H.264 trailers from Apples site? is there a way to download the videos, or stream them with something other then Quicktime?

you can save them if you have quicktime pro, no idea about streaming, maybe VLC (edit: plays video jumpy, aac 5.1 is mute, also with wrong audio info displayed, now sure who to blame )?

720p plays (almost, there is some banding) fine on p4/3gigs, there are problems playing them with nero (weirds skips, jumps, ect, but i didnt really do any proper testing on whats up.)

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edit: another machine (dual xeon 2.8), nero plays iceage 720p video fine - smooth, no banding, there is no 5.1 audio, possibly something wrong with my setup / what aac decoder will work?.

kingkong, nero plays 1080p video (not fine), there is audio as well (stereo aac).