[FEAT] add PDF as output

[bytebone]

Hey there,

this project came in clutch when I needed to batch generate thumbnails for a large folder of video files. The one feature I was missing though is to concatenate all produced thumbnails into neatly organized PDF files, appropriately sized to a pagesize, and properly compressed to not get too large.

If you're not sure what I am thinking of, consider this report from a professional (and paid) media software:

This would require moving the file information to the left of the thumbnails, and by default only generating one line of 3-4 thumbnails, depending on what fits best. Then making sure these stacked images dont exceed the width and height of standard page sizes.

Since I've been looking for go projects to better myself with, I'd offer to jump on and try to add this if you think of it as useful. I've played around with imagemagik a little to get this to work and have some sort of solution using magick montage, I'd just have to figure out how to properly implement this (or a more efficient solution) into the code.

[kmou424]

Sounds good, we can add an cmd argument to specify file type of output. Then process them in different ways.

[kmou424]

Create a branch to develop this feature. And we should not let too many external programs as dependencies if possible.