I've had a pretty poor experience with HTML 5 video. It stutters far more than flash and in particular it does very weird things when I try to skip around in videos. I'll miss flash.
So my old tactic of open 5 tabs, maximise and watch one by one is completely nerfed
To prevent YouTube from switching sources when resizing the content, select a specific quality first (it defaults to “Auto”). I wouldn't be surprised if there were browser extensions that automatically do this (e.g. always choose the highest quality).
I switched to forcing HTML a while ago so can't test. Either way, I'll try that - thank you :)
Of course computer itself plays 1080p h264 perfectly fine in mplayer, so I might end up writing javascript that fires mplayer with mp4 link (to stream rather than downloading whole clip) instead of displaying video in the browser :(
There used to be mplayer plugin for firefox a loong time ago, nowadays all browsers use building unoptimized codecs.
The fact that somebody down-voted me for adding a relevant anecdote, but happens to go against the tide of this threads opinion(ie: FU Flash), it's pretty indicative of the extremely poor voting etiquette around here.
Your anecdote isn't relevant, because I don't know what hardware you run, and it's likely that most other readers aren't using the same hardware. Your time would be better spent filing a bug report.