There are several problems, if you want to make a picture slideshow, which shall be transmitted through Whatsapp:
- You need a Whatsapp compatible video format.
- Pictures may have different formats / resolutions.
- Smart-phone displays have wide screens.
- Whatsapp's upper bound of a video's file size is 16MB.
- How to make subtitles?
In what follows, you will find my quick and dirty solution. Note that you need Linux with GNU parallel, ImageMagick, and ffmpeg installed.