Add webp to image core media types

[mattgarrish]

I'm not 100% sure on the citing for this. There are a couple of google developer pages for the container and lossless bitstream specifications, so I added both. Are these formal enough references for W3C @iherman? (I don't see what else we could cite, though.)

Partially addresses #1344. Issue of a reliable source specification still to be determined.

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[iherman]

@mattgarrish is right that the WebP normative references are iffy. See my comment in #1344 (comment).

Until this is resolved, we should not merge this imho.

[dauwhe]

I'm trying to shame Google on Twitter about this :)

[dauwhe]

It appears that the developer is not interested in standardization:

The specs used a reference are:
lossy VP8: https://tools.ietf.org/html/rfc6386

• Lossless: https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification
• Container: https://developers.google.com/speed/webp/docs/riff_container

The (large) time investment it takes going to ISO or similar for official spec was diverted to making libwebp better :)

They do not address the question of registering the media type. Is that possible without a specification from a standards body?

[iherman]

See #1344 (comment). I propose to keep this PR open and discuss the more general issue.

[svgeesus]

That is just handwaving.

If there is a decent enough specification then it is trivial to register a Media Type.

I offered to help registering it.

[iherman]

I offered to help registering it.

Thank you @svgeesus

[iherman]

This issue was discussed in a meeting.

• RESOLVED: Merge #1347 with an additional warning about support for WebP

View the transcript

Issue on WebP
Wendy Reid: #1347
Wendy Reid: I thought we were waiting for an answer from someone
Ivan Herman: perhaps in a non-normative fashion
… it’s not registered anywhere
Dave Cramer: When we were talking about WebP, it’s an internal doc at Google
… the person who wrote the spec didn’t want to register the media type
… various W3C people have offered to help register the type
… some concern that google could change the spec
Wendy Reid: Chris Lilley had offered to help with media type registration
Ivan Herman: what we could do is… we can do two things
… one, keep the PR open and come back in a year
… two, we put it in with a big yellow warning saying this is a feature that may be taken out
… because status is unclear
… I don’t know which of the two is better
Dave Cramer: I would be curious to see if WebP works in existing reading systems
Hadrien Gardeur: It works in readium
Ivan Herman: does it rely on google engine?
Hadrien Gardeur: Whatever is around, if you’re on iOS 14 it works there, on android it has worked for a few years
… has worked on Android for a while
Ivan Herman: what about thorium?
Hadrien Gardeur: Thorium uses chromium, so it works, even on a mac
Ivan Herman: even on a mac?
Hadrien Gardeur: yes
… I would expect it would work in a lot of places, because it’s supported by many webviews
… probably won’t work on RMSDK
Garth Conboy: I agree with Dave and Hadrien
… I think we should put it in with a warning
… that might drive more learning
Matt Garrish: a third option is reconsider mandating support in the spec
… there are custom implementations, we need a baseline… I don’t know if that’s something the spec needs to say
… and not getting into the whole restricting things that are outside of our control
… that’s a separate discussion
Wendy Reid: I support putting in WebP with a warning
Ivan Herman: to follow up on what matt said
… we are already in an awkward situation
… there are some media types where we are explicit
… we don’t have a list of video types
Dave Cramer: Difference between video and images, 99% of EPUBs have images, but very few EPUBS have video
George Kerscher: I would love to see us start testing video in the titles
… people are waiting for that quality of content being added to educational materials
… putting it in the spec would protect from Google IP
Hadrien Gardeur: ivan hinted at the larger question
… can we tackle that larger question?
… I don’t think it’s sustainable
… it belongs in a best practices doc
… we are not consistent with how we deal with HTML/CSS vs images
Gregorio Pellegrino: for the image format I’m concerned about e-readers
… there are a lot of old e-readers which would never support webp
… and new content wouldn’t work
Garth Conboy: I would like to get to Hadrien’s discussion
… we can have a vote now about WebP
… then return to the larger issue
… should we move image specificity to video specificity
Ivan Herman: garth almost said what I wanted to say
… let’s decide on webp today
… and open an issue on github
Proposed resolution: Merge #1347 with an additional warning about support for WebP (Wendy Reid)
Ivan Herman: +1
Garth Conboy: +1
Matt Garrish: +1
George Kerscher: +
Hadrien Gardeur: +1
Bill Kasdorf: +1
Charles LaPierre: +1
Juliette McShane: +1
Gregorio Pellegrino: 0
Brady Duga: 0
Wendy Reid: +1
Matthew Chan: 0
George Kerscher: I think it’s great if we put this in
Toshiaki Koike: 0
Laurent Le Meur: +1
George Kerscher: if it moves to a best practice that’s fine
Ben Schroeter: 0
Masakazu Kitahara: 0
George Kerscher: but we get the format into implementations and documented
Wendy Reid: that’s another discussion
Resolution #2: Merge #1347 with an additional warning about support for WebP

[iherman]

The latest information is that WebP will move to IETF in the coming months. We can have good hope that, by the time the spec is final, the issues around WebP will be gone.

@dauwhe @shiestyle @wareid @HadrienGardeur