ffmpeg

Ah, well that narrows it down. From the documentation:

The syntax foo-%03d.jpeg specifies to use a decimal number composed of three digits padded with zeroes to express the sequence number. It is the same syntax supported by the C printf function, but only formats accepting a normal integer are suitable.

When importing an image sequence, -i also supports expanding shell-like wildcard patterns (globbing) internally, by selecting the image2-specific -pattern_type glob option.

And the "image2" documentation goes into a little more detail:

A sequence pattern may contain the string "%d" or "%0Nd", which specifies the position of the characters representing a sequential number in each filename matched by the pattern. If the form "%d0Nd" is used, the string representing the number in each filename is 0-padded and N is the total number of 0-padded digits representing the number. The literal character ’%’ can be specified in the pattern with the string "%%".

And skimming the rest of the documentation, it seems these are pretty much the only two patterns you'll have to worry about, which makes the conversion much simpler - they can all be replaced by regexes of the form \d+ or \d{N}.