No module named av: why installing FFmpeg may not fix the Python import

There are two integration paths

PyAV is installed as av. Its installation documentation distinguishes binary wheels from source builds that use FFmpeg development libraries.1 An external ffmpeg executable is a separate diagnostic target.

python -m pip show av
python -c "import av; print(av.__version__); print(av.library_versions)"

Use the original interpreter. The second command imports the installed package; run it only for a trusted installation. If a build fails, preserve the first missing header, library or compiler error rather than repeatedly retrying the final wheel failure.

Our suggested next step depends on the caller. For a Python import failure, investigate PyAV. For an external-process failure, record the executable selected by the node. For decoding or encoding errors, record the container, codecs and complete first exception.

Test a short video you created and keep the original untouched. Compare one change at a time. A successful import does not prove every codec works, and a system FFmpeg upgrade is not the default repair for a missing Python module.

Related checks

• aiohttp and requests: a missing library is not a connection failure
• Keep a reproducible ComfyUI repair record without exposing secrets

Research draft. No local/GPU reproduction or independent editorial sign-off. Upstream statements and our recommendations are distinguished.