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

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