Crate mp3rgain 

mp3rgain

Lossless MP3 volume adjustment library - a modern mp3gain replacement.

This library provides lossless MP3 volume adjustment by modifying the global_gain field in each frame’s side information.

Features

• Lossless: No re-encoding, preserves audio quality
• Fast: Direct binary manipulation, no audio decoding
• Compatible: Works with all MP3 files (MPEG1/2/2.5 Layer III)
• Reversible: Changes can be undone by applying negative gain

Optional Features

• replaygain: Enable ReplayGain analysis (requires symphonia)
  • Track gain calculation (-r flag)
  • Album gain calculation (-a flag)

Example

use mp3rgain::{apply_gain, apply_gain_db, analyze, GainOptions, Channel};
use std::path::Path;

// Simple gain adjustment: +2 steps (+3.0 dB)
let frames = apply_gain(Path::new("song.mp3"), 2).unwrap();
println!("Modified {} frames", frames);

// Or specify gain in dB directly
let frames = apply_gain_db(Path::new("song.mp3"), 4.5).unwrap();

// Builder pattern for advanced options
GainOptions::new(5)
    .wrap(true)
    .undo(true)
    .apply(Path::new("song.mp3")).unwrap();

// Channel-specific gain with undo support
GainOptions::new(3)
    .channel(Channel::Left)
    .undo(true)
    .apply(Path::new("song.mp3")).unwrap();

Modules

• analysis - MP3 file analysis and amplitude detection
• gain - Gain adjustment operations and the GainOptions builder
• ape - APEv2 tag reading, writing, and management
• replaygain - ReplayGain loudness analysis
• mp4meta - MP4/M4A metadata handling
• aac - AAC bitstream parsing (feature-gated)

Technical Details

Each gain step equals 1.5 dB (fixed by MP3 specification). The global_gain field is 8 bits, allowing values 0-255.

Re-exports

pub use analysis::analyze;

pub use analysis::find_max_amplitude;

pub use analysis::is_mono;

pub use analysis::ChannelMode;

pub use analysis::MaxAmplitudeResult;

pub use analysis::Mp3Analysis;

pub use analysis::MpegVersion;

pub use ape::delete_ape_tag;

pub use ape::read_ape_tag;

pub use ape::read_ape_tag_from_file;

pub use ape::write_ape_tag;

pub use ape::ApeItem;

pub use ape::ApeTag;

pub use ape::TAG_MP3GAIN_ALBUM_MINMAX;

pub use ape::TAG_MP3GAIN_MINMAX;

pub use ape::TAG_MP3GAIN_UNDO;

pub use ape::TAG_REPLAYGAIN_ALBUM_GAIN;

pub use ape::TAG_REPLAYGAIN_ALBUM_PEAK;

pub use ape::TAG_REPLAYGAIN_TRACK_GAIN;

pub use ape::TAG_REPLAYGAIN_TRACK_PEAK;

pub use error::Error;

pub use error::Result;

pub use gain::apply_gain;

pub use gain::apply_gain_db;

pub use gain::db_to_steps;

pub use gain::steps_to_db;

pub use gain::undo_gain;

pub use gain::Channel;

pub use gain::GainOptions;

pub use gain::GAIN_STEP_DB;

pub use gain::MAX_GAIN;

pub use gain::MIN_GAIN;

pub use id3v2::delete_id3v2_replaygain;

pub use id3v2::read_id3v2_replaygain;

pub use id3v2::undo_gain_id3v2;

pub use id3v2::write_id3v2_replaygain;

pub use id3v2::write_id3v2_undo;

pub use id3v2::Id3v2ReplayGain;

Modules

aac

AAC bitstream parser for locating global_gain fields in M4A/MP4 files.

analysis

ape

error

Custom error types for mp3rgain.

gain

id3v2

ID3v2 TXXX frame storage for ReplayGain and undo tags.

mp4meta

MP4/M4A metadata handling for ReplayGain tags

replaygain

ReplayGain analysis module