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};
use std::path::Path;

// Apply +2 gain 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();

Technical Details

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

Modules

mp4meta

MP4/M4A metadata handling for ReplayGain tags

replaygain

ReplayGain analysis module

Structs

ApeItem

APEv2 tag item

ApeTag

APEv2 tag collection

Mp3Analysis

Result of MP3 file analysis

Enums

Channel

Channel selection for independent gain adjustment

Constants

GAIN_STEP_DB

MP3 gain step size in dB (fixed by format specification)

MAX_GAIN

Maximum global_gain value

MIN_GAIN

Minimum global_gain value

TAG_MP3GAIN_ALBUM_MINMAX

TAG_MP3GAIN_MINMAX

TAG_MP3GAIN_UNDO

MP3Gain specific tag keys

TAG_REPLAYGAIN_ALBUM_GAIN

TAG_REPLAYGAIN_ALBUM_PEAK

TAG_REPLAYGAIN_TRACK_GAIN

ReplayGain tag keys

TAG_REPLAYGAIN_TRACK_PEAK

Functions

analyze

Analyze an MP3 file and return gain statistics

apply_gain

Apply gain adjustment to MP3 file (lossless)

apply_gain_channel

Apply gain adjustment to a specific channel only (lossless)

apply_gain_channel_with_undo

Apply channel-specific gain and store undo information in APEv2 tag

apply_gain_db

Apply gain adjustment in dB (converted to nearest step)

apply_gain_with_undo

Apply gain and store undo information in APEv2 tag

apply_gain_with_undo_wrap

Apply gain with wrapping and store undo information in APEv2 tag

apply_gain_wrap

Apply gain with wrapping (values wrap around instead of clamping)

db_to_steps

Convert dB gain to MP3 gain steps

delete_ape_tag

Delete APEv2 tag from file

find_max_amplitude

Find maximum amplitude in an MP3 file Returns (max_amplitude, max_global_gain, min_global_gain)

is_mono

Check if an MP3 file is mono

read_ape_tag

Read APEv2 tag from file data

read_ape_tag_from_file

Read APEv2 tag from file

steps_to_db

Convert MP3 gain steps to dB

undo_gain

Undo gain changes based on APEv2 tag information

write_ape_tag

Write APEv2 tag to file