The format specs are named following a very simple naming convention described in the Formats page.
Generating thumbnails in JPG formats and a very cool WebP animation with multiple scenes:
Static thumbnails in JPG, PNG and WebP format
Simple Format pattern: jpg|png|webp:$widthx$height
Generate thumbnails in either jpg, png or webp format from the source video.
3 ways to generate thumbnails
By using the number option which is the default, you choose to generate a given number of thumbnails. The images will be spaced equally.
By using offsets (Array), you specifically select 1 or many offsets in second where you want to take the thumbnail.
With interval, you specify an interval in seconds.
Here is an example of how to generate multiple sprite files and a VTT file.
Static Images Parameters
Simple Format pattern: gif|webp_anim:$widthx$height
Create an animation image from the source video. Width must be <= 600px.
The height is automatically calculated according to the given width and the original aspect ratio.