Thumbnail WebP images as WebP

[tastytea]

I'm testing it since about 3 months (on a single user server) and it works fine.

Closes: #11840
Signed-off-by: Ronny (tastytea) Gutbrod tastytea@tastytea.de

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[clokep]

At #7586 (comment) @erikjohnston said:

On the other hand, it might make sense to generate webp previews for webp images. This one also works fine. What do you think?

Given some devices can't render webp I think it makes sense for thumbnails to be in a more widely supported format.

I think in the (almost) 3 years since that comment support for WebP has increased, back in May of 2020 Safari (on both iOS and macOS) didn't support WebP, where it looks like it is widely supported now. The only folks who might have an issue are people on macOS < 11 where transparency of WebP is not supported. This shouldn't be any worse than what we currently do of thumbnailing to JPEG! (Latest IE 11 and KaiOS Browser 2.5 also don't support WebP, but those are hardly used.) I'm a little less confident about mobile support (I'm not sure how mobile clients usually render images), but have asked internally about that.

tl;dr I think it is reasonable to support this, but I have a few questions:

• Do you know if our minimum version of pillow supports thumbnailing to WebP?
• Do we need to ensure any operating system libraries are installed to support WebP?

Can we now update the tests at tests/rest/media/v1/test_media_storage.py to have expected output? It seems that in #7586 it was not "deterministic" so was left out?

[tastytea]

tl;dr I think it is reasonable to support this, but I have a few questions:

• Do you know if our minimum version of pillow supports thumbnailing to WebP?
• Do we need to ensure any operating system libraries are installed to support WebP?

Looks like it is supported since pillow 2.4.0 from 2014 and it needs libwebp.

[squahtx]

Looks good. Now that we're relying on libwebp, we should also:

• Update the installation instructions in docs/setup/installation.md
  https://github.com/matrix-org/synapse/blob/4eb2f4e02b83c90519a8a55c562d1fafab7caf0b/docs/setup/installation.md#platform-specific-prerequisites
  The package name is libwebp-dev for Debian/Ubuntu/Raspbian, libwebp-devel for CentOS/Fedora and libwebp-devel for OpenSUSE
• Add a check for webp support to synapse/rest/media/v1/__init__.py
  https://github.com/matrix-org/synapse/blob/develop/synapse/rest/media/v1/__init__.py

[clokep]

Cross-referencing matrix-org/matrix-spec#453.

[tastytea]

Updated instructions and added check; also fixed the zlib check error message while i was there.

[squahtx]

Thanks for updating the docs so thoroughly!

Just one minor thing left.

[tastytea]

updated since the location of synapse/rest/media/v1/thumbnailer.py changed to synapse/media/thumbnailer.py.

[clokep]

I suspect this needs something like MSC4011 by the way to unstick the current issue.