centos7用html5播放器,centos 7, firefox 52.2.0, html5, h264 not working.

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tested:

Centos 7

firefox 52.2.0 and 57.0

52.2.0 is the one from the centos distribution, 57.0 is the one I got when I

downloaded from mozilla's website tonight.

Two different machines, one my production machine and one a fresh install.

visit the site http://www.youtube.com/html5 . I get checkmarks by

htmlvideoelement

media source extensions

webm vp8

mse & webm vp9

but I do not get checkmarks by:

h.264

mse & h.264

What I see online is that I'm supposed use firefox and visit about:config

and set various flags to certain values. I'm supposed to set

media.fragmented*

various suffixes, to various values, but none of these

appear on my machine (either version of firefox). I also read that these

flags are obsolete/deprecated from firefox 44.0 on, so i guess that's why.

media.mp4.enabled true

media.mediasource.enabledtrue

media.mediasource.mp4.enabledtrue

media.mediasource.webm.audio.enabledtrue

media.mediasource.webm.enabledtrue

So those are what I have, but those aren't the ones I'm supposed to have,

unless what I'm reading online is obsolete.

I checked plugins (open menu --> add-ons --> plugins) and it claims

openh264 is automatically installed. and active.

Chrome, by the way, works--that is, the youtube site gives me six

checkmarks.

So, does anyone know of a modern answer to whether firefox on linux

can do html5 video? Are there some rpms I might be missing? Seems

like that couldn't be the issue given that chrome works. (I've driven

myself a little bit nuts on this, I guess.) Yeah, yeah, i could use chrome

but I like firefox and it seems like firefox ought to work.