Video decoding on these machines is all about CPU power, and the consensus seems to be that a G4 CPU (even a pair of them) cannot handle 1080p at any reasonable frame rate, with 720p performance being marginal at best, even on the fastest G4s. Even G5s can struggle with HD video playback, particularly 1080p at higher frame rates.
No, no, and no. Bottom line : get CorePlayer. All right I don't know how the thread starter can have good results with Quicktime (that sounds very weird), but what I do know is what you can accomplish with the mighty CorePlayer.
Check my other post about Vimeo on a 733mhz single G4.... 1080p must be a JOKE for a G5, I am pretty sure about that. OK I don't have a G5, but my G4 can handle some HD 1080p (from OK to very very nicely).
Think about it.... Back in 1993 you could edit DVD-like quality (640X480) compressed video on a 40 mhz Quadra and system 7. Damn it. By today's point of view, 40 mhz sounds like the computer doesn't even have enough power to boot.
Apps apps apps.... optimization, coding.... everything is about it. Imho, the hardware made back in the G4 days is still overkill for any 2D 3D video application you see on the market today. I have no doubt a game like Skyrim SHOULD work on a G4. Programmers just don't work hard anymore. When you HAVE to find a trick because the hardware isn't that great, you work hard and get it working. Nowdays there is no need -- computers have more cores every day.
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Now OP, what the f..... is your trick, because I want to know how you manage better results on a computer lower than mine in every aspect.