Since my own Powermac did not run HTML5 fast enough until I upgraded the processor, porting Fab's work to AOS4 probably doesn't make sensde.
Most hardware running AOS4 would not be powerful enough to display HTML5 code any better than my original 933Mhz G4.
Erm, on my Pegasos II / G4, I can play 360p youtube clips at full speed using 30% CPU in overlay mode, unlike the "normal/windowed" mode that is heavier and may skip frames, because it has to go through (soft-)cairo rendering. So you should really use the "fullscreen" option (which plays in fullwindow, in practice).
Make sure to read OWB's readme in YouTube section. There are a few things to know :
- adding one userscript (scripts/youtube_fullscreen_fix.js) to unbreak Youtube's HTML5 fullscreen mode.
- adding another one to make non-HTML5 Youtube link play through the builtin HTML5 player anyway (scripts/youtube.js).