[trunnell]

Scanning the comments here and I don't see anyone addressing the elephant in the room: PATENTS.

After a bit of searching, it's unclear what degree of "patent risk" comes with JPEG XL. JPEG historically was subject to patent troll lawsuits until the patent expired in 2006.

Please note that it's not enough for there to be a "royalty-free reference implementation" of JPEG XL, even if it's licensed with Apache 2.0, because you can't be sure from a glance that the Apache license patent grant includes all relevant patents. If you care about open source and free formats, you should look for two things: a comprehensive patent pool transferred to the standards body AND a royalty-free patent license to anyone with no strings attached.

The game here is that companies with potential claims over some techniques used within codecs have an incentive to withhold their patents from the official pool until years after adoption. Then they sue the biggest users of the codec (like Google) for obscene sums of money. That's why ALL of the patents used in a codec must be assigned to the standards body for open licensing, and you have to be SURE that none are withheld. This is difficult.

AVIF (and it's standards body, the AOM) was created in part (I believe) to solve this very problem. All the major tech companies are members and they've effectively agreed to a patent truce with regards to codecs.

This is arguably the most important commercial concern in distributing a browser for free that includes codecs. If you ship unlicensed codecs, some random company can crawl out of the woodwork 5 year later and sue you for a billion dollars.

In my view, AVIF only needs to be competitive with compression and quality. It patent risk is so low that it is the obvious choice. AVIF is truly open, there are multiple implementations, and its reason for existing is to solve the codec patent problem.

Source: I was near the activities within Netflix that helped found the AOM.

Disclaimer: I'm not a lawyer and this isn't legal advice; also I'm several years out of date w.r.t. JPEG XL specifically, so I'd be happy to be corrected about the relevant patent risk. Maybe someone has better info?

[neandrake]

Did google cite patents as one of the reasons they removed support initially? I thought it was all around lack of benefits and difficulty of maintenance.

[Sakos]

Apparently Microsoft was granted this patent on rANS in early 2022 (https://patents.google.com/patent/US11234023B2/en) and Google deprecated JPEG XL support late 2022. JPEG XL uses rANS, so I think there's some likelihood that this motivated Google to change their focus. Google didn't mention anything about this in their reasoning, but would they have mentioned patent issues publicly if that were the real reason? Google isn't obligated to tell us everything and the reasons they gave always felt weak and weirdly dismissive.

[JyrkiAlakuijala]

JPEG XL doesn't use the kind of rANS that Microsoft has patented.

JPEG XL decides the codes at encoding time and does context modeling the same way as WebP lossless and Brotli, by deciding which entropy codes to use explicitly.

Microsoft's rANS patent is supposedly centralized around updating rANS codes at decoding time (based on past symbols). This is slightly more efficient for density, but much slower and may negate the speed benefits that rANS brings. For practical implementations JPEG XL/Brotli way is quite a bit better.