New config parameter --viewer.codec defaults to VP8, but allows H264

[machenmusik]

Fixes #1325.

[tancik]

Im fine with making H264 the default, but Im curious, are there any specific reasons to prefer it over VP8?

Also with H264 I see alot of spurious printing

[machenmusik]

H264 has better compression (perhaps better for remote viewers) -- and may facilitate hardware encoding, which should be somewhat faster / less burdensome for the server.

Not sure where the log spam from libx264 is from, probably somewhere in aiortc etc.?
If we can't figure out how to quash, and it's annoying, feel free to change default from H264 back to VP8
(although then we should change the description).

[tancik]

I've dug around and haven't found any obvious ways to disable the logging. Lets keep the default to VP8 for now and then consider changing if we figure it out.

[machenmusik]

Done.
(What I've seen about PyAV logging doesn't seem to work on the libx264 spam...)

[machenmusik]

Sidebar: I notice that when doing dynamic image size calculation (e.g. changing viewer position/orientation), there are quite a number of different sizes, which seem to cause a good number of encoder changes. I wonder it would be better to have fewer discrete sub-frame sizes, to thrash a bit less, similar to downsampling... but that's probably more important if hardware encoding.

[tancik]

LGTM