AVIF: the small one this bench will not run yet

AVIF is a still picture stored as a single frame of AV1 video. It inherits that codec’s machinery — many block sizes, many prediction modes, a search that considers a great number of ways to describe each region — and that machinery is why it routinely produces the smallest file of anything a browser can display.

It is also why encoding one is slow. The decoder is cheap and the encoder is expensive, which is an excellent trade for a website serving a million readers and a poor one for a page that has to encode your picture while you wait for it.

There is no AVIF column in the converter unless your browser can write one itself, and this page exists instead of a bundled encoder that would lie about the wait. The numbers behind the decision are below rather than in a footnote: they were measured on this project, from a file that was downloaded and run, and nothing here is quoted from a table.

The rows below are about software a file will actually be handed to, not about a specification. A format is supported when the person you sent it to can open it.

This is the whole problem. On this project's own measurement, a single-threaded WebAssembly build of the reference encoder took 3.3 seconds to write one 12-megapixel picture on an Apple-silicon laptop at its fastest useful setting, and 12.9 seconds at a moderate one — before any quality search, which multiplies that by up to seven. The encoder binary is 3.3 MB. On a mid-range phone the honest number is minutes, and there is no way to present minutes as a wait. See BUILD-NOTES in the repository for the measurements.

• Encoding is slow enough to be a product decision rather than a detail, which is why this site does not offer it yet.
• Decoding is cheap, so a page that serves AVIF is fast even where writing one was not.
• Some encoders default to a chroma configuration that softens saturated reds more than the file size would suggest.
• Re-encoding an AVIF as another AVIF is a second lossy pass, not a copy.

Pictures served from a web page, encoded once on a machine that has time, to an audience using current browsers. That is the case AVIF was designed for and it wins it clearly.

It is the wrong answer for a file you are sending to a person rather than serving to a browser. Windows will not preview one without an extra codec installed, and most desktop software of any age simply will not open it — and a file the recipient cannot open is not a smaller file, it is a failed delivery.

Encoding happens on this machine; the file stays where it is.