Hi HN, I am the author.
mp3rgain is a rewrite of the classic mp3gain tool for adjusting MP3 volume
without re-encoding. The original mp3gain has not been updated since 2015 and
does not work well on modern systems.
Technical approach:
MP3 files have a global_gain field (8 bits, 0-255) in each frame side
information that controls playback volume
mp3rgain modifies these values directly, no audio decoding needed
Changes are completely reversible (original values stored in APEv2 tags)
ReplayGain analysis uses symphonia for pure Rust decoding
Why rewrite instead of patch? The original C codebase had accumulated
20 years of patches and was difficult to maintain. A clean Rust
implementation was more practical.
Currently available via Homebrew tap and cargo. Working toward Homebrew
core inclusion (needs community adoption/stars).
Happy to answer questions about the implementation.
