ffmpeg specific jpeg encoding

Question

I'd like to convert a movie into jpeg in a specific way. I was wondering if ffmpeg can help here.

What I need to achieve is every 25 frames from the movie needs to be written in a single .jpeg file - one under another. So that from a single movie I get

part1.jpg
  frame1
  frame2
  frame3
  ...
  frame25

part2.jpg
  frame26
  frame27
  frame28
  ...
  frame50

...

Can this be done without dumping the file into separate .jpegs and then modifying them?

Answer 1

I'm far from an ffmpeg expert, but I don't believe ffmpeg is capable of this level of image processing by itself. I think, in order to achieve your desired goal, you'll need this workflow:

1. Extract all frames to individual, temporary image files with ffmpeg;
2. Combine a sequence of 25 temporary image files into a single final image with a JPEG tool (such as montage from the ImageMagick package);
3. Repeat step 2 until all final images have been created.

This should be fairly easy to script, but it will take up a lot of disk space while it's working.