Remove JPEG poster image?

[slightlyoff]

All modern browsers now support WebP. Any reason to keep the JPEG code?

[justinribeiro]

Yeaaaa it's a fair callout. I have branch that strips it; the only reason I ahven't merged it as of yet is I'm still trying to determine if the older "WebP generated with delay by YouTube" is still a thing—doesn't seem to be in my testing.

I think I'll prep it to merge as part of a general perf-revision next couple of weeks (there's some other stuff that needs to get chop chopped too).