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https://github.com/francisrussell/zoog

Updates Opus headers and R128 tags to normalize playback volume for non-R128-aware players.
https://github.com/francisrussell/zoog

audio normalization ogg opus vorbis xiph

Last synced: 9 months ago
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Updates Opus headers and R128 tags to normalize playback volume for non-R128-aware players.

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README 

          
# Zoog: Zero Opus Output Gain



[![Zoog crate](https://img.shields.io/crates/v/zoog)](https://crates.io/crates/zoog)

[![Zoog documentation](https://docs.rs/zoog/badge.svg)](https://docs.rs/zoog)



Zoog is a Rust library that consists of functionality that can be used to

determine the loudness of an Ogg Opus file and also to rewrite that file with

new internal gain information as well as loudness-related comment tags. It also

has functionality for purely manipulating comment tags of both Ogg Opus and Ogg

Vorbis files.



Zoog currently contains two tools, `opusgain` and `zoogcomment`. `opusgain` can

be used to:



* set the output gain value located in the Opus binary header inside Opus files

  so that the file plays at the loudness of the original encoded audio, or of

  that consistent with the

  [ReplayGain](https://en.wikipedia.org/wiki/ReplayGain)  or [EBU R

  128](https://en.wikipedia.org/wiki/EBU_R_128) standards.



* write the Opus comment tags used by some music players to decide

what volume to play an Opus-encoded audio file at.



It is intended to solve the "Opus plays too quietly" problem.



`zoogcomment` can be used to list, replace or modify the comment tags of Ogg

Opus and Ogg Vorbis files. Its usage is roughly based on that of

`vorbiscomment` though many options have different naming for improved clarity.



Although `zoog` exposes a library, its API is unstable and this package is

released on [crates.io](https://crates.io/) primarily to allow access to the

command-line tools. The API is documented however, and the reading the source

may prove useful to anyone else wishing to work with Ogg Opus files.



## `opusgain`



`opusgain` adjusts the Opus binary header for playback at a specific volume and

will always generate the `R128_TRACK_GAIN` tag and the `R128_ALBUM_GAIN` tag

(when in album mode) such that files will play at an appropriate volume in

players that support these tags, and at a more appropriate volume in players

that don't. Existing `R128_ALBUM_GAIN` tags will be stripped when not in album

mode.



`opusgain` (unlike its predecessor `zoog`) decodes Opus audio in order to

determine its volume so that it's possible to be certain that all generated

gain values are correct without making assumptions about their existing values.



The following options are available (run `opusgain --help` for usage):



* `-p PRESET, --preset=PRESET`



  It is recommended to specify this value explicitly, as the default

  may change.



  * `original`: Set the output gain in the Opus binary header to 0dB. In

    players that do not support `R128` tags, this will cause the Opus file to

    play back at the volume of the originally encoded source. You may want this

    if you prefer volume normalization to only occur via tags.



  * `rg`: Set the output gain in the Opus binary header to the value that

    ensures playback will occur at -18 LUFS, which should match the loudness of

    ReplayGain normalized files.  This is probably the best option when you

    have a player that doesn't know about Opus `R128` tags, but:

    * does support ReplayGain for the other file formats you use, and/or

    * the files you play have been adjusted in a player-agnostic way

      ([mp3gain](http://mp3gain.sourceforge.net/) and

      [aacgain](http://aacgain.altosdesign.com/) can do this) to the ReplayGain

      reference volume.



  * `r128`: Set the output gain in the Opus binary header to the value that

    ensures playback will occur at -23 LUFS, which should match the loudness of

    files produced by `opusenc` from FLAC files which contained ReplayGain

    information. This is the gain level intended by the Opus authors.



  * `no-change`: Do not change the output gain in the Opus binary header.



* `-o MODE, --output-gain-mode=MODE`



  * `auto`: Set the output gain in the Opus binary header such that each track

    is album-normalized in album mode, or track-normalized otherwise. In album

    mode, this results in all tracks having the same output gain value as well

    as the same `R128_ALBUM_GAIN` tag.



  * `track`: Set the output gain in the Opus binary header such that each track

    is track-normalized, even if album mode is enabled. In album mode, this

    results in all tracks being given different output gain values as well as

    different `R128_ALBUM_GAIN` tags, but their `R128_TRACK_GAIN` tags will be

    identical.  Unless you know what you're doing, you probably don't want this

    option.



* `-a, --album`: Enables album mode. This causes `R128_ALBUM_GAIN` tags to also be

  generated. These tell players that support these tags what gain to apply so

  that each track in the album maintains its relative loudness. By default the

  output gain value for each file will be set to identical values in order to

  apply the calculated album gain, but this behaviour can be overridden using

  the `--output-gain-mode` option.



* `-j N, --num-threads=N`: Use `N` threads for processing. The default is to use the

  number of cores detected on the system. Larger numbers will be rounded down

  to this value. To avoid high disk space usage during processing, or a large

  number of temporary files left around after an error, only one file will be

  rewritten at a time regardless of the number of threads.



* `-c, --clear`: Remove all `R128` tags from the specified files. The output

  gain of each file is unchanged, regardless of the specified preset.



* `-M`, `--minimize-mtime-change`: Attempts to apply the smallest increment

  possible (filesystem dependent) to the modification time of the file. This is

  deliberately not a preserve in order to avoid misleading backup/data-transfer

  programs that use this information to determine if a file has changed. On

  modern filesystems (ext4, APFS, btrfs) this is typically a nanosecond, but

  could be up to two seconds on older filesystems (ext3, FAT32).



* `-n, --dry-run`: Displays the same output that `opusgain` would otherwise

  produce, but does not make any changes to the supplied files.



* `-I PATH_PROCESSING_MODE, --interpret-paths=PATH_PROCESSING_MODE`



  This option controls how the supplied paths are interpreted.



  * `files-singles` (default): Each supplied path must be to a file. Files are

    normalized independently, with any album tags being removed. It is an error

    to supply a folder.



  * `files-album`: Each supplied path must be to a file. Files are treated as

    all belonging to the same album and album normalization tags will be

    generated.  It is an error to supply a folder. This option is equivalent to

    supplying the `-a` or `--album` flag.

  

  * `folders-are-albums`: Each file path supplied is treated as a single, with

    album tags being removed. Each supplied folder path is explored (including

    recursive traversal of sub-folders) with all found Opus files being treated

    as part of a single album. This option therefore makes it possible to apply

    multiple album normalizations in a single `opusgain` invocation. Which

    files inside folders are considered Ogg Opus files is controlled by the

    `--file-extensions` option.



    For example, if you had the files:



    ```

    a.opus

    album1/b.opus

    album1/c.opus

    album2/e.opus

    album2/f.opus

    d.opus

    ```



    Then `opusgain -I folders-are-albums *` in that folder would be expanded

    (by the shell on Linux/MacOS or by `opusgain` on Windows) to `opusgain -I

    folders-are-albums a.opus album1 album2 d.opus` with `a.opus` and `d.opus`

    being treated as singles and `album1` and `album2` being normalized as

    independent albums.



* `-e FILE_EXTENSIONS`, `--file-extensions=FILE_EXTENSIONS`: When folders are

  passed on the command line to be searched for files, this option determines

  what file extensions are considered to be Ogg Opus files. Multiple extensions

  may be supplied separated by commas. By default this value is `opus`, but

  `ogg,opus` could be supplied to assume that all found `.ogg` files are Ogg

  Opus as well.



If the internal gain and tag values are already correct for the specified files,

`opusgain` will avoid rewriting them.



Sequentially multiplexed or "chained" Ogg Opus streams are not supported.



`opusgain` supports Unix shell style wildcards under Windows, where wildcards

must be handled by the application rather than expanded by the shell.



## `zoogcomment`



`zoogcomment` can be used to delete, append, replace and list the comments

located in an Ogg Opus or Ogg Vorbis file.



The following options are available (run `zoogcomment --help` for usage):



* `-l, --list`: List all tags in the file in `NAME=VALUE` format. This will be to

  standard output unless `-O` is specified.



* `-m, --modify`: Tags specified using `-t` or `-I` will be appended to the

  specified file. Tags matching patterns specified using `-d` will be

  removed from the existing tags on the file.



* `-r, --replace`: All existing tags in the file will be removed and will be

  replaced with those specified using `-t` or `-I`.



* `-t NAME=VALUE, --tag NAME=VALUE`. The specified tag is will be added to the

  file in modify or replace mode.



* `-d NAME[=VALUE], --delete NAME[=VALUE]`. Specifies either a tag name, or a

  name-value mapping to be deleted. All tags that match the pattern will be

  removed, not just the first. This option is only valid in modify mode.



* `-e, --escapes`: In all tag input/output either on the command-line or

  to/from a file escapes will be used for line-feeds (`\n`), carriage returns

  (`\r`), backslashes (`\\`) and the null character (`\0`). All other escapes

  are invalid. This option makes it possible to specify tags which contain

  newlines which would otherwise fail to be parsed correctly from a comment

  file.



* `-I COMMENT_FILE, --tags-in COMMENT_FILE`: In the modify and replace modes,

  the tags to added will be read from this file in addition to those specified

  on the command line. Tags are read in `NAME=VALUE` format, with one tag per

  line. If `-` is specified for the file name, tags will be read from

  standard input.



* `-O COMMENT_FILE, --tags-out COMMENT_FILE`: In list mode, tags will be

  written to this file. Tags are written in `NAME=VALUE` format, with one tag per

  line. If `-` is specified for the file name, tags will be written to standard

  output.



* `-M`, `--minimize-mtime-change`: Attempts to apply the smallest increment

  possible (filesystem dependent) to the modification time of the file. This is

  deliberately not a preserve in order to avoid misleading backup/data-transfer

  programs that use this information to determine if a file has changed. On

  modern filesystems (ext4, APFS, btrfs) this is typically a nanosecond, but

  could be up to two seconds on older filesystems (ext3, FAT32).



* `-n, --dry-run`: Displays the same output that `zoogcomment` would otherwise

  produce, but does not make any changes to the filesystem.



`zoogcomment` only has knowledge of UTF-8. Usage on systems where UTF-8 is not

the character encoding scheme in use may encounter issues.



## Build Instructions 



If you do not have Cargo, install it by following the instructions

[here](https://doc.rust-lang.org/cargo/getting-started/installation.html).



Clone the Git repository:



```$ git clone https://github.com/FrancisRussell/zoog.git```



Inside the cloned repository:



```cargo build```



or 



```cargo build --release```



for a release build.



Built binaries can be found in `target/debug` or `target/release`.



## Installation via `cargo`



At the command line, simply run

```

$ cargo install zoog

```



`opusgain` and `zoogcomment` should now be available in the path.



## Releases



Zoog binaries for Windows, MacOS and Linux can be found on the [releases

page](https://github.com/FrancisRussell/zoog/releases/). Only the Linux

binaries have undergone any testing at present.



## About Ogg Opus Volume Normalization



### Background



Opus-encoded audio files contain an [‘output

gain’](https://tools.ietf.org/html/rfc7845) value which describes a gain to be

applied when decoding the audio. This value appears to exist in order to ensure

that loudness changes to Opus files are *always* applied, rather than being

dependent on decoder support for tags such as `REPLAYGAIN_TRACK_GAIN` and

`REPLAYGAIN_ALBUM_GAIN` which are used in Ogg Vorbis, but *not* Opus.



The in-header value was intended to correspond to the album gain with

[RFC 7845](https://tools.ietf.org/html/rfc7845) defining the tag

`R128_TRACK_GAIN` for single-track normalization. It seems the original intent

of the output gain was to eliminate the need for an album gain tag, however

`R128_ALBUM_GAIN` was later added for album normalization.



### The problem



When encoding an Opus stream using `opusenc` from a FLAC stream which has

embedded ReplayGain tags, the resulting Opus stream will have the output gain

field set in the Opus header. The gain value will be chosen using [EBU R

128](https://en.wikipedia.org/wiki/EBU_R_128) with a loudness value of -23

[LUFS](https://en.wikipedia.org/wiki/LKFS), which is 5 dB quieter than

ReplayGain.



The presence of either `R128_TRACK_GAIN` or `R128_ALBUM_GAIN` tags will allow

players that support these to play tracks at an appropriate volume. However, in

audio players that do not support these tags, track will likely sound extremely

quiet (unless your entire music collection is normalized to -23 LUFS).



Even more problematically, using `opusenc` with a FLAC file that does not have

embedded ReplayGain tags will produce a file that plays at the original volume

of the source audio. This difference in behaviour means that it's not possible

for players that do not support `R128` tags to assume that different Opus files will

play at a similar volume, despite the presence of the internal gain header.



Even if a player does support the `R128` tags, this is not enough to correctly

play Opus files at the right volume. In the case described above, `opusenc`

will use the internal gain to apply album normalization, meaning that it does

not generate a `R128_ALBUM_GAIN` tag. Without this, it's not possible for a

music player to play a track at album volume without again assuming that the

internal gain corresponds to an album normalization at -23 LUFS.



## Q & A



### How is loudness calculated?



Loudness is calculated using [ITU-R

BS.1770](https://en.wikipedia.org/wiki/LKFS). This is the standard used by [EBU

R 128](https://en.wikipedia.org/wiki/EBU_R_128) for measuring loudness and the

one intended for use when calculating Opus `R128` tags.



### What's with the name `zoog`?



`zoog` stands for "Zero Opus Output Gain" and was the name of the original tool

in this project. It served a similar purpose to `opusgain` but used the existing

`R128` tags to determine file volume rather than decoding audio directly.



`zoog` was deprecated because the issues around whether it is possible to

assume that a track is album normalized made it possible to break album

normalization if it occured via the ouput gain value and not the

`R128_ALBUM_GAIN` tag.



### When should I use `opusgain` versus `loudgain`



If you only play Opus files in players which support `R128` tags, then use

[loudgain](https://github.com/Moonbase59/loudgain).



You should use `opusgain` if you play Ogg Opus files in players that do not

support `R128` tags and would like them to play at either their original

volume, or at the volumes suggested by ReplayGain or EBU R 128.



Once you have set the internal gains of a set of Opus files to the desired

values, then `loudgain` is likely preferable for any future tag updates related to

normalization.



### How can I check if `opusgain` is working correctly?



Applying `opusgain` to various test files then reviewing the diagnostic output

and `R128` tags generated by [loudgain](https://github.com/Moonbase59/loudgain)

when applied to the rewritten files is helpful in this regard.



## Disclaimer



Please see LICENSE. Unless you have a source you can easily reconstruct your

Ogg Opus and/or Vorbis files from, the author recommends making a backup of any

files you intend to modify first, and running `opusinfo` afterwards on any

processed files.



## References



1. [RFC 7845 - Ogg Encapsulation for the Opus Audio Codec](https://www.rfc-editor.org/rfc/rfc7845.txt)

2. [Vorbis I Specification](https://www.xiph.org/vorbis/doc/Vorbis_I_spec.html)

3. [Ogg Vorbis identification header](https://wiki.xiph.org/OggVorbis)