The closest thing I'm aware GMS2 has is
Code:
audio_sound_get_track_position(audio);
I don't believe there's anything equivalent to "audio_track_length(audio)". One thing you could do, however potentially tedious, is manually add your track lengths in total seconds into an array or ds_list, so you could use
Code:
var percent = audio_sound_get_track_position(audio) / sound_lengths[| audio]
.
I'm not really sure if that would work. I'm just waking up
I did find this extension on the marketplace that might suit your needs:
https://marketplace.yoyogames.com/assets/430/exaudio