https://bugs.freedesktop.org/show_bug.cgi?id=71570
--- Comment #1 from Kertesz Laszlo laszlo.kertesz@gmail.com --- Sorry for not being contrtructive with this reply, but hardware decoding with flash player was always shoddy even with nvidia for which it was intended in the first place and bug reports like this should be directed to the flash developers first since the flash plugin is not open source and has issues with nvidia too (read below).
Also note that the plugin destined for browsers that are not Chrome will not be updated anymore so the only possible solution would be filing a bug for the Chrome version of Flash (which in my experience is worse than the Firefox&al flash on radeon at the moment).
The only site which works ok ish is youtube (there might be others), but hw decoding enabled crashes the plugin on many other sites. This happened with nvidia (i had a nvidia 8200 IGP which had vdpau B class which worked very well with VDPAU otherwise) and it still happens with my A8-5500 (Radeon 7560 IGP) with the latest git Mesa, kernel, drm.
So its most likely a Flash issue.
Funny thing is that the AMD GPU with radeon/VDPAU works better with the legacy flash on Seamonkey/Firefox (nvidia had inverted colors sometimes on youtube and HW decoding wasnt working consitently)...