Issue with AV1 encoder

[paulrouget]

AV1 is important as it is poised to become the next VP9.

We use this version libaom 3.7.0 (https://aomedia.googlesource.com/aom/+/refs/tags/v3.7.0) which seems to freeze ffmpeg during encoding. We should either figure out with the Google team what's going on, or switch to SVT-AV1 (libsvtav1) or rav1e (librav1e).

[mi-g]

with the current vdhcoapp/ffmpeg, the command line below does the job inside one thread, at very low speed (0.0663x)

~/git/vdhcoapp/dist/linux/x86_64/ffmpeg "-y" "-i" "/tmp/vdh--3163143-h28yZKXDuJeV-.tmp" "-i" "/tmp/vdh--3163143-l9Qz7TItvz8o-.tmp" "-c:v" "av1" "-strict" "experimental" "/home/mig/dwhelper/Weekly.mp4"

where /tmp/vdh--3163143-h28yZKXDuJeV-.tmp is a audio aac file and /tmp/vdh--3163143-l9Qz7TItvz8o-.tmp is an av1 video file (using another vp9 video file does not seem to change the low performance).

[paulrouget]

Normally the strict experimental option should not be necessary. If it is necessary, that means there's something funky going on (the experimental flag was removed after aom v2, we use v3).

[mi-g]

The same command without the `-strict experimental" produces an ffmpeg error:

[libaom-av1 @ 0x5597c5ef9700] The encoder 'libaom-av1' is experimental but experimental codecs are not enabled, add '-strict -2' if you want to use it.
Conversion failed!