Adobe's whining about bad Linux and why in Windows acceleration is possible:
To be short Adobe says the video acceleration is not possible in Flash for Linux because all Video decoding APIs (including VDPAU) in Linux can not put decoded video stream back to flash plugin so it can mix it with static graphics like buttons in player gui.
How the acceleration looks now in Linux (for all apis):
application-----mpeg4 video stream---->acceleration API (vdpau for example)--decoded video in RGB-->display screen
What Adobe wants for flash plugin:
flash plugin---mpeg4 video stream----->acceleration API (vdpau for example)--decoded video in RGB-->flash plugin--->display
Adobe also complains there is plenty of decoding APIs in Linux instead of one common for all.
So the video acceleration blockers for Adobe are:
1. plenty of video decoding APIs ("Welcome to the Thicket") instead of one
2. no decoded RGB video route back from GPU to flash plugin
Windows does not have these two blockers because:
1. There is only one API possible: DXVA
2. DXVA allows decoded RGB video route back from GPU to flash plugin