mp3rgain

mp3rgain is a modern reimplementation of the classic mp3gain / aacgain tools, written in Rust. It adjusts the volume of MP3 and AAC/M4A files by rewriting the global_gain field in each frame — the audio is never decoded or re-encoded, so quality is preserved bit-exactly and every change can be undone with a single command.

Unlike tools that only write ReplayGain tags (which many hardware players, car stereos, and apps ignore), mp3rgain bakes the corrected volume into the file itself, so it plays at the right level everywhere. It uses the ReplayGain 1.0 algorithm (89 dB reference) for Track and Album gain analysis, fully compatible with the original mp3gain.

Key features:

• Truly lossless gain adjustment for MP3 and AAC/M4A (the only actively maintained CLI for lossless AAC bitstream gain)
• Fully undoable — mp3gain-compatible undo tags restore originals exactly
• Drop-in mp3gain/aacgain replacement: identical CLI flags, TSV output, and tags (works with beets and existing scripts)
• Zero dependencies: a single static binary, no ffmpeg required
• Parallel multi-threaded analysis
• Native GUI app (mp3rgui) with drag-and-drop for macOS, Windows, and Linux
• ~2 MB multi-arch Docker image for containerized batch jobs (e.g. Plex library maintenance)
• Installable via Homebrew, winget, AUR, PPA, Debian, Nix, MacPorts, Docker, and Cargo