About

mp3binder joins multiple MP3¹ files into one without re-encoding. It writes ID3v2 tags and chapters² for each file.

Why?

Older mp3players (e.g. simple stereos for children), are not always capable of playing multiple files in the correct order. Joining them into one file removes this limitation. Or sometimes a single mp3 file is more practical than a directory of files.

How

This tool builds upon Darren Mulholland's wonderfully simple mp3cat with the corresponding low-level library mp3lib which performs all the heavy lifting. The tool adds id3v2 tag support with the help of the id3v2 library by Albert Nigmatzianov.

Features

mp3binder:

• combines multiple mp3 files without re-encoding
• can embed a cover image (jpeg, png) to the output file
  • either via the command line option: --cover
  • or by copying from an input file, e.g. the first file: --tcopy 1
  • or automatically if the folder of the mp3 files contain a folder.jpg or cover.jpg file
  • the automation can be disabled with the command line option --nodiscovery
• can add files between each files (e.g. silence)
  • either via the command line option: --interlace
  • or automatically if the folder of the mp3 files contain a _interlace.mp3 file
  • the automation can be disabled with the command line option --nodiscovery
• can write chapters based on the id3v2 title of the input files
  • it can be disabled with the command line option: --nochapters
• can write id3v2 tags to the output file via the command line option: --tapply 'TIT2="My Title",TALB="My album"'
  • the key can be any valid tag from the id3v2 standard

Screenshot

Note: color added for clarity

Usage

mp3builder joins multiple MP3 files into one without re-encoding.
It writes ID3v2 tags and chapters for each file.

Usage:
  mp3builder file1.mp3 file2.mp3 [flags]

Examples:
Calling 'mp3builder' with no parameters in the directory containing the mp3 files
is equivalent to: 'mp3builder .', which is the same as 'mp3builder *.mp3' and
binds all mp3 files to 'foldername.mp3'.

Flags:
      --nodiscovery        no discovery for well-known files (e.g. cover.jpg)
      --nochapters         does not write chapters for bounded files
      --cover string       use image file as artwork
      --verbose            prints verbose information for each processing step
      --force              overwrite an existing output file
      --interlace string   interlace a spacer file (e.g. silence) between each input file
      --output string      output filepath. Defaults to name of the folder of the first file provided
      --tapply string      apply id3v2 tags to output file.
                           Takes the format: 'key1="value",key2="value"'.
                           Keys should be from https://id3.org/id3v2.3.0#Declared_ID3v2_frames
      --tcopy int          copy the ID3 metadata tag from the n-th input file, starting with 1
      --lang string        ISO-639 language string used during string manipulation
                           (e.g. uppercasing non-english languages) (default "en-GB")
  -h, --help               help for mp3builder
  -v, --version            version for mp3builder

Examples

Files to be merged can be specified as a list of filenames:

$ mp3binder one.mp3 two.mp3 three.mp3

Alternatively, an entire directory of .mp3 files can be merged:

• $ mp3binder or $ mp3binder . (the current directory is used)
• $ mp3binder foo (the files in the 'foo' directory are used)
• $ mp3binder *.mp3 (the shell expands all mp3 files as individual shell-sorted parameters)

ID3 tags can be copied from the n-th input file:

$ mp3binder --tcopy 1 one.mp3 two.mp3 three.mp3

ID3 tags could also be set manually. The name of the tag must be according to https://id3.org/id3v2.3.0#Declared_ID3v2_frames:

• $ mp3binder . --tcopy 1 --tapply "TRCK=42,TIT2='My sample title'"
• $ mp3binder . --tapply "TIT2=\"It's like that\""

Please notice the surrounding quotes and ensure proper quoting.

Silence between each tracks via interlace file

Based on: http://activearchives.org/wiki/Padding_an_audio_file_with_silence_using_sox

Create a silence track: sox -n -r 44100 -c 2 silence.mp3 trim 0.0 3.0

If the input material is FBR (fixed bit rate), generate the silence track with the same fixed bit rate using the '-C' option: sox -n -r 44100 -c 2 -C 192 silence.mp3 trim 0.0 3.0. The shell command file one.mp3 gives information about the bit rate of a file.

And apply: mp3bind --interlace silence.mp3 01.mp3 02.mp3

Build instructions

Building is always more complex then just calling build (e.g. adding version information into the binary or naming the binary or optimize the binary by stripping debug information). Instead of a Makefile, a Taskfile.yml is used that holds the instructions for Task. 'Task' is not mandatory but simplifies the workflow. Once installed (instructions), 'Task' provides an executable task that can be called with custom actions.

For example cross compilation for multiple platforms is achieved with task build-all, and for the current platform with task build. Plain go would be: go build .\cmd\tui\ without build time optimizations and settings (e.g. version information).

The Taskfile.yml gives good hints which commands and options are executed if the developer don't want to use task. In the end 'Task' it's just a simple task runner (collection of commands).

Golang 1.18

As of today (January, 2022), golang 1.18 with generics is not yet released, but betas are available. Please refer to: https://go.dev/blog/go1.18beta2

Install gotip

go install golang.org/dl/go1.18rc1@latest
go1.18rc1 download

Install latest gopls

1. Either in Codium / VS Studio Code: "Go: Install/Update Tools"

2. Or manually. Example for POSIX based systems:

mkdir /tmp/gopls && cd "$_"
gotip mod init gopls-unstable
gotip get golang.org/x/tools/gopls@master golang.org/x/tools@master
gotip install golang.org/x/tools/gopls

Configure VSCode/Codium

1. View > Command Palette
2. Go: choose Go environment
3. select go1.18rc1

Footnotes

1. formally: MPEG-1 Audio Layer III or MPEG-2 Audio Layer III ↩

2. specification ↩