As part of the DAM asset processing functionality, every author instance has been provided with an installed copy of the FFmpeg CLI tool. This is to be used with inbuilt com.day.cq.dam.handler.ffmpeg.FFMpegWrapper class (OOTB Day Communique 5 DAM Video Extensions bundle i.e. com.day.cq.dam.cq-dam-video) to generate new video renditions, which starts with a call to determine the input asset size.
There is a problem because it tries to match CLI output to a specific regular expression:
" Stream.* Video: .* d+xd+.*"
i.e. one where there are exactly FOUR spaces before "Stream".
However the ffmpeg 4.4-static that has been provided on the instance (which is the current version) outputs TWO spaces in the line this regex is looking for:
Stream #0:0(und): Video: vp9, yuv420p(tv, bt709, progressive), 560x320, q=2-31, 30 fps, 1k tbn (default)
Thus AEM FFMpegWrapper (cq-dam-video 5.12.8) fails to obtain the necessary details and the transcoding process does not even start, breaking the workflow.
Wait for and apply Service Pack 14.