mp3rgain is a modern tool designed for lossless MP3 volume adjustment by modifying the global_gain field in each frame's side information. This approach preserves audio quality while enabling permanent volume changes without re-encoding.
Key Features:
Lossless & Reversible Adjustments: Volume changes are applied directly to the file, allowing for reversible adjustments without any loss of audio quality.
ReplayGain Analysis: Supports track and album gain analysis, ensuring consistent listening levels across tracks or albums.
AAC/M4A Support: Compatible with AAC and M4A files, expanding its utility beyond MP3s.
Cross-Platform Compatibility: Works seamlessly on macOS, Linux, and Windows (including x86_64 and ARM64 architectures).
Command-Line Compatibility: Fully compatible with the original mp3gain command-line interface, providing a familiar workflow for users.
Audience & Benefit:
Ideal for audiophiles, music producers, and anyone requiring precise volume control over their audio files. By eliminating the need for re-encoding, mp3rgain ensures that adjustments are lossless, maintaining the highest possible audio quality while achieving consistent listening levels across tracks or albums.
The software can be installed via winget on Windows for a streamlined experience.
README
mp3rgain
Lossless MP3/AAC volume adjustment - a modern mp3gain / aacgain replacement written in Rust
mp3rgain adjusts MP3 and AAC volume without re-encoding by modifying the global_gain field in each frame. This preserves audio quality while achieving permanent volume changes.
> The only actively maintained CLI for lossless AAC/M4A bitstream gain adjustment.
> aacgain (the historic CLI) has been unmaintained since ~2009 and rarely builds on modern 64-bit systems. foobar2000 also offers re-encode-free AAC gain on MP4/MKA via its "Apply ReplayGain to file content" feature (Windows GUI only, no undo). mp3rgain is the actively maintained, cross-platform, scriptable, undoable option for headless / batch / CI use.
Features
CLI lossless AAC bitstream gain: re-encode-free global_gain rewrite for AAC/M4A — replacing the long-abandoned aacgain, with -u undo (foobar2000's GUI equivalent has no undo path)
Lossless & Reversible: No re-encoding, all changes can be undone (MP3 and AAC)
ReplayGain: Track and album gain analysis for MP3 and AAC/M4A
Zero dependencies: Single static binary (no ffmpeg, no mp3gain, no aacgain)
Cross-platform: macOS, Linux, Windows (x86_64 and ARM64)
mp3gain / aacgain compatible: Drop-in replacement with identical CLI
GUI Application: Native desktop app for drag-and-drop workflow
Binaries for all platforms are also available from GitHub Releases.
Quick Start
# Normalize a single track (ReplayGain)
mp3rgain -r song.mp3
# Normalize an album
mp3rgain -a *.mp3
# Manual gain adjustment (+3.0 dB)
mp3rgain -g 2 song.mp3
# Undo changes
mp3rgain -u song.mp3
# Show file info
mp3rgain song.mp3
Migrating from mp3gain?
Already running mp3gain (or aacgain) in a script, Dockerfile, or CI pipeline? mp3rgain is a drop-in replacement — the CLI flags, the TSV output format, and the APEv2 mp3gain_undo tag are all mp3gain-compatible, so existing parsers (e.g. beets) keep working unchanged. For most setups, migration is a one-line substitution:
sed -i 's/\bmp3gain\b/mp3rgain/g' your_script.sh
See docs/migrating-from-mp3gain.md for the full flag equivalence table, Dockerfile/CI substitution patterns, tag interop notes, and the small set of intentional behaviour differences. Bit-level verification lives in docs/compatibility-report.md.
GUI Application
A native GUI application (mp3rgui) is available for users who prefer a graphical interface.
> macOS manual download: If you see "mp3rgui cannot be opened" warning, run:
> bash > xattr -cr /path/to/mp3rgui.app >
> This is not needed when installing via Homebrew.
Command-Line Options
Option
Description
-r
Apply Track gain (ReplayGain)
-a
Apply Album gain (ReplayGain)
-g <i>
Apply gain of i steps (1 step = 1.5 dB)
-d
Modify target dB level (use with analysis)
-u
Undo gain changes
-k
Prevent clipping
-R
Process directories recursively
-n
Dry-run mode
-j / --threads
Worker threads for analysis (default: auto, 0=auto, 1=serial)
-o [fmt]
Output format: text, json, tsv (default: tsv if no argument)
Run mp3rgain -h for the full list of options.
ReplayGain analysis runs in parallel by default
(std::thread::available_parallelism() worker threads). Use -j 1 or
MP3RGAIN_THREADS=1 for the legacy serial path. See
docs/perf-parallel.md for the design and
real-corpus benchmark numbers.
Documentation
Migration Guide - Drop-in replacement for mp3gain: flag equivalence, sed/Dockerfile/CI substitution patterns, beets config
Use Cases - Integration examples (beets, headroom, etc.)
Download Stats - Weekly download trends across all platforms
Why mp3rgain?
The original mp3gain has been unmaintained upstream since ~2015 (though distribution maintainers continue to apply security patches). aacgain, its AAC counterpart, has been unmaintained since ~2009 and is effectively unbuildable on modern 64-bit systems. mp3rgain is a modern, memory-safe replacement written in Rust that covers both.
AAC/M4A on the CLI is the differentiator. Among CLIs, rsgain / loudgain / FFmpeg either only write ReplayGain tags (which non-compliant players ignore) or re-encode the audio. foobar2000 has a comparable "Apply ReplayGain to file content" feature for AAC in MP4/MKA, but it is Windows GUI only, has no undo, and is unsuited for batch, headless, or container workflows. mp3rgain fills the cross-platform, scriptable, reversible niche.
mp3rgain implements the ReplayGain 1.0 algorithm (89 dB reference level) for full compatibility with the original mp3gain / aacgain. Loudness values will differ from EBU R128/LUFS-based tools (foobar2000, loudgain, ffmpeg loudnorm).
Use mp3rgain in Docker / CI
Official multi-arch images (linux/amd64, linux/arm64) are published to GHCR:
ghcr.io/m-igashi/mp3rgain:latest
ghcr.io/m-igashi/mp3rgain:v2 # latest 2.x
ghcr.io/m-igashi/mp3rgain:v2.3.0 # exact version
The image is built FROM scratch with a fully static (musl) binary — no
shell, no runtime deps, ~2 MB. Drop-in replacement for mp3gain in
containerized batch / cron pipelines (e.g. Plex maintenance windows):
# Normalize a music library by mounting it into the container
docker run --rm \
-v /path/to/music:/music \
ghcr.io/m-igashi/mp3rgain:latest -r -R /music
# Run as your own user so written files keep correct ownership
docker run --rm \
--user "$(id -u):$(id -g)" \
-v /path/to/music:/music \
ghcr.io/m-igashi/mp3rgain:latest -r -R /music
Because the entrypoint is the binary itself, all mp3rgain flags work
exactly the same as the host CLI (-r, -a, -R, -k, -u, …).
Library Usage
use mp3rgain::{apply_gain, analyze};
use std::path::Path;
let frames = apply_gain(Path::new("song.mp3"), 2)?; // +3.0 dB
let info = analyze(Path::new("song.mp3"))?;
