You can convert audio/ video files to mp3 format using ffmpeg by:
ffmpeg -i input.mov -c:v copy -c:a libmp3lame -q:a 4 output.mp3
This is handy when you trim the video/ audio when using QuickTime on macOS (since the extension will be .mov or .m4a)
You can link to any specific time in a mp3 file, just by adding a query string #t=<time> to the mp3 file url.
For example, if you want to link to 18:15 of a mp3 file, 18*60 + 15 = 2295, you can use the url https://cdn.changelog.com/uploads/jsparty/231/js-party-231.mp3#t=2295.
Reference: Jest Preview on JS Party Podcast