Add support for blurhash (MSC2448)

[turt2live]

MSC: matrix-org/matrix-spec-proposals#2448

While the image loads, we can show a blurred version of it (calculated at upload time) so we don't have a blank space in the timeline.

Example:

Done with a community hat on:

Signed-off-by: Travis Ralston <[email protected]>

[turt2live]

self-selecting this as a community PR as it's p2 relative to other work.

[jryans]

@turt2live Has Product been alerted to this idea? If not, I think we either need a review from them, or it needs to be behind a labs flag.

[turt2live]

@jryans it definitely doesn't need a labs flag imo, but product and design will need to provide input at some point. Currently this is relatively low priority as it's an MSC implementation and not finalized yet, so it's already serving its intended purpose.

I'll take this out of the review queue as it's somewhat failed to get review, and I don't expect/anticipate it to land anytime soon anyways.

[t3chguy]

So this PR has only a subset of the support for MSC2448

• Showing blurhashes on incoming timeline images
• Sending blurhashes as part of thumbnail generation for images & videos

Not yet done:

• Blurhashed stickers
• Blurhashed room avatars
• Blurhashed member avatars
• Blurhashed URL previews
• Blurhashed inline images

[turt2live]

In all honesty, those missing areas were deliberately out of scope for this PR

[t3chguy]

I was just summarising the current state.
I think the only one that I'll need to do for first cut will be local blurhashing for e2ee

[t3chguy]

Screen.Recording.2021-05-21.at.21.22.11.mov

This PR also fixes video thumbnailing in general, turns out it was totally broken at least in chrome, always yielding fully black frames.

[jryans]

Thanks, this looks great to me! There's some amount of updating to do to resolve conflicts, but otherwise it looks good. 😄