this one is probably set up better
https://patchstorage.com/audio-player-and-speed-pitcher-pd-vanilla/#downloadssampler_help.pd

here is a setup you could try and finnish this
helpfile2.pd

if you drive a phasor object to play a audio file. you can decide how fast the phasor goes from 0 to 1 . and therfore you know when it hits 1 which means the end of the audio file. you need to see someone drive a phasor with line because there are more than a few ways
pd_help_file1.pd

gemhead goes at the top . go look at the help file diagram for pix-texture.

if nothing works, you can always cam your Pi camera image with a second camera compatible with gem I dont know I havnt tried it it might be mp2

@jameslo one-cycle-display_gem.pd this needs declare lib gem