Partyflow is a self-hostable music release manager (think Bandcamp) with a built-in on-demand transcoder, written in Java 17. The media formats it offers are customizable, but it ships with a large collection of pre-defined formats tuned to provide the best balance between filesize and audio fidelity.
Some of its headline features are gapless playback, native ReplayGain 2 support, metadata management (including album art formats not supported by FFmpeg), and a slick lightweight JS-optional web UI with customizable colors.
Partyflow is no longer on GitHub. Please head over to the Forgejo repo. You can make issues and PRs using a GitHub account.