At first glance you just need to change get_tracks_from_content. Rather than running $content through do_shortcodes,
- split it by linebreaks (or whitespace?) and discard empty lines, or anything that isn’t an URL
- probably make the strip_tags call at this point, on each value you have left
- pass the URLs into track_shortcode as
[ "src" => $url ], plus any other common metadata you want to set here - concatenate the results to make a new $content
- continue with the
// Replace last commacode.