i think i got mine to do (most of?) what you were looking for.
Code:
[Nemo Action]
Active=true
Name=pix2vid
Comment=create video from images
Exec=<pix2vid.sh %F>
Icon-Name=image
Selection=any
Extensions=jpg;png;bmp;gif
Quote=double
Terminal=true
using
ffmpeg's concat demuxer.
Code:
#!/bin/bash
for f in "$@"
do
echo "file '$f'\rduration 3" >> ./mylist.txt
done
ffmpeg -f concat -safe 0 -i ./mylist.txt -vf scale=500:300 out.mp4
of course you may want to change where that list is and probably wipe it (maybe echo /dev/null ./mylist.txt?) after the video is made so you can make another, but i was able to choose 3 photos all with whitespaces. all of mine happened to be png's as well. i'm not sure what might/would happen if different formats were selected. most of the examples on ffmpeg.org used one single format to make the video.
that duration bit might not be exactly what you were looking for, but in general i think it is similar to what you were trying to set with -framerate (which for some reason threw an error when i tried to use it. maybe it doesn't work with concat?). without a specified duration, concat wouldn't make the video. there should be a way around it, but that is the best my limited skills have come up with for now.