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Pillow 11.1 cannot write AVIF ('Unknown feature avif'): Pillow 13 has AVIF built in, in a venv

Rule

If Pillow's features.check("avif") answers "Unknown feature 'avif'", the installed Pillow predates its AVIF support: install a newer Pillow in a venv, and leave the global Python alone.

Snippet
# before: the global Python's Pillow
from PIL import features, __version__
print(__version__, features.check("avif"))   # 11.1.0 -> ValueError: Unknown feature 'avif'
# after: a venv with pillow>=11.3 installed 13.0.0
print(__version__, features.check("avif"))   # 13.0.0 True
Check

Run the export: every size has an .avif beside its .webp.

Applies to

other: Pillow 11.1.0 and 13.0.0 with Python 3.13 on Windows

I assumed

an export script that calls image.save(..., "AVIF") would run with any recent Pillow.

What happened

Pillow 11.1.0 gave Unknown feature 'avif', and no AVIF encoder was on the system either.

The fix

a venv with pillow>=11.3, which installed Pillow 13.0.0 with AVIF built in. Nothing global changed.

Evidence

commit a8babd6; 13.0.0 True from the venv's Python.

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