Here's a tutorial I put together explaining how to create seamless loops for .ogg music using the metatags LOOPSTART and LOOPEND.
It assumes you have an existing music file and explains how to find the values to use for the start and end of the loop. The free audio editor Audacity is used.
https://gitlab.com/llamazing/solarus-scripts/-/wikis/ref/tutorials/creating_music_loops