Cool demo. The 'gm montage' step isn't working for me and I'm finding its options completely non-intuitive. I produced a series of 1979 PNGs from a 66-second video, and when I stitch them with:

  gm montage -borderwidth 0 -geometry +0+0 -tile x1 *.png image.jpg

I get an image that is 45, not 1979, pixels wide. In fact the number of PNGs used as input and the resulting width have a nonlinear relationship:

    # of 1-px wide PNGs     Resulting width (px)
    5                       3
    10                      4
    20                      5
    50                      8
    100                     10
    200                     15
    500                     23
    1000                    32
    1979                    45

Note that I made a couple changes: to speed things up I used "-vf crop=1:1080:280:0" with ffmpeg to skip the separate cropping step and output 1x1080 PNGs, and my version of gm didn't accept the -border option so I assumed you meant -borderwidth.

What's up with the crazy widths on the result? What is GraphicsMagick doing?