AVIF output depends on the image libraries installed on the hosting server. Two sites running PHP can have different codec support, so the same preparation choice may work on one host and be unavailable on another.
Convert Image to AVIF checks for usable AVIF output during encoding. It reports a codec error when that capability is missing.
Start with the host support summary
The Image Preparation admin screen reports available image functions. An AVIF function still needs its underlying codec to work, so the actual processing result is the final check.
Use a small demonstration image first. If it succeeds, review its byte size and appearance at the intended display dimensions. Quality controls encoding; it does not resize the picture.
If the host cannot encode AVIF, use PNG, JPEG or WebP as appropriate rather than repeatedly uploading the same file. Hosting support may be able to explain whether an updated PHP/GD build is available.
Output support does not expand the input list
This tool set accepts static JPEG, PNG and WebP uploads. The AVIF tool creates an AVIF output from those supported inputs. It does not promise to decode an uploaded AVIF, HEIC file or animated sequence.
The receiving system also matters. A website image slot and a document upload form may accept different formats, regardless of what the server can generate.
Keep the source because reencoding removes original metadata and colour profiles. A generated AVIF should be reviewed for its intended use, not treated as an archival replacement for the original.
The local fixture used for this release lacked AVIF encoding, and its unavailable codec response was checked. That limitation is stated openly; it is not evidence that every compatible hosting environment lacks the format.
Reference: PHP AVIF encoding documentation.