Feature suggestion: Intro mode

[HT-7]

Overview Description:

We have a JVC boombox from the 2000s that has an "Intro" feature where it plays the first 10 seconds of a CD track.

Please add such an ability to celluloid, but with the option to set a custom number of seconds.

This feature is not all that important, it is just for the wishlist.

[gnome-mpv]

You can already do this with the length option.

To make it toggleable, put something like this in the input config file: a cycle-values length none 10.