Crop filter isn't applied to mixing transitions?

Question

When I apply a -filter crop parameter to my melt script, it only seems to crop each clip - not the -mix mixing between clips.

melt \
clip1.mp4 in=180 out=360 \
-mix 20 -mixer luma -mixer mix:-1 \
clip2.mp4 in=660 out=960 \
-mix 20 -mixer luma -mixer mix:-1 \
clip3.mp4 in=1080 out=1300 \
-filter crop left=420 right=420 \
-consumer avformat:"output.mp4" ab=128k crf=23 -profile "./square_profile.txt"

Is there some other way I can apply a crop that works with -mix transitions?

Answer 1

Solving my own problem:

The solution is to add a crop for each file, using -attach instead of -filter

melt \
clip1.mp4 in=180 out=360 \
-attach crop left=420 right=420 \
-mix 20 -mixer luma -mixer mix:-1 \
clip2.mp4 in=660 out=960 \
-attach crop left=420 right=420 \
-mix 20 -mixer luma -mixer mix:-1 \
clip3.mp4 in=1080 out=1300 \
-attach crop left=420 right=420 \
-consumer avformat:"output.mp4" ab=128k crf=23 -profile "./square_profile.txt"