You have to change video decoding to be via the cpu not via the allwinner libs (. this is the reason why youtube video are only in SD. If i remind correctly the setting for that is in media_codecs.xml or something similar. Later I will check the correct name and the changes for video decoding. Will be better to use allwinner libs with hardware decoding but it’s require some development - firefoxos did some changes for proper mpeg4 decoding with allwinner libs.
p.s Yes media_codecs.xml is the correct file but for some reason I didn’t push my changes Later I will make new push with fix for video decoding