I often use the cropdetect filter to figure out how to crop and scale a source file. It would be useful if dcpomatic used this during analyzing and displayed the results to the user.

Depending on the source format, it can take som time. Maybe it would be best to take make sample measurements at intervals (depending on source file length) to keep the analyze time down.

Here is a command line example of how I use this functionality:

$ ffmpeg -i The\ Invisible\ Woman-73929989.mp4 -vf cropdetect=24:2:0 -f null - |& grep -o crop=.:.:.:. | sort | uniq -c | sort -rn
159862 crop=640:272:0:46
23 crop=-638:-362:640:364
7 crop=640:268:0:48
1 crop=640:270:0:48
1 crop=640:188:0:84
1 crop=6:-362:440:364
1 crop=446:20:0:88
1 crop=222:-362:224:364
1 crop=0:-362:446:364

This source is letterboxed scope inside a 640x364 container.

In this case I would first crop to 640x268 and then scale to 2048x858.

Thanks!