Volume normalization for MP4?

[Rudd-O]

Today I tried an experiment whereby I replaygained (using command replaygain from the musictoolbox package, based on the library rgain3) an MP4 video.

Playing it back in Music Assistant played the sound no problem, but the information box that shows whether the video has volume normalization data showed nothing (it said it was being fixed to -6 dB, which is my fallback when there is no volume normalization info). The file has definitely beeen modified and the program said so:

[rudd-o@nas Folder]$ replaygain replaygained.mp4 
Checking for Replay Gain information ...
  replaygained.mp4:none
Calculating Replay Gain information ...
  replaygained.mp4:-7.69 dB
  Album gain: -7.69 dB
Writing Replay Gain information to files ...
  replaygained.mp4:done
Done

Why isn't it being picked up? What formats of volume normalization are read by Music Assistant? A pointer to the relevant code will also be helpful to me. What tooling should I use?

Ancillary question: my existing tooling normalizes at what they say is a "reference level of 89 dB". Is that actually compatible with the calculations that Music Assistant does?

[Rudd-O]

[rudd-o@nas Folder]$ /usr/bin/replaygain --help
usage: replaygain [-h] [--version] [-f] [-d] [-r REF] [--mp3-format {default,replaygain.org,legacy,ql,fb2k}] [--help-gst] [--no-album] [--show] AUDIO_FILE [AUDIO_FILE ...]

Apply or display Replay Gain information for audio files. This program is similar to the likes of 'vorbisgain' or 'mp3gain': You pass in some files, they are analyzed and receive their
share of Replay Gain. The difference is that replaygain supports several file formats, namely Ogg Vorbis (anything you'd put into an Ogg container, actually), Flac, WavPack and MP3.
Also, it allows you to view existing Replay Gain information in any of those file types.

positional arguments:
  AUDIO_FILE

options:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -f, --force           Recalculate Replay Gain even if the file already contains gain.information.
  -d, --dry-run         Don't actually modify any files.
  -r, --reference-loudness REF
                        Set the reference loudness to REF dB (default: 89 dB).
  --mp3-format {default,replaygain.org,legacy,ql,fb2k}
                        Choose the Replay Gain data format for MP3 files. The default setting should be compatible with most decent software music players, so it is generally not
                        necessary to mess with this setting. Check the README or man page for more information.
  --help-gst            Show GStreamer options.
  --no-album            Don't write any album gain information.
  --show                Don't calculate anything, simply show Replay Gain information for the specified files. In this mode, all other options save for '--mp3-format' are ignored, for
                        they would make no sense.

[OzGav]

What codec is used inside the mp4 container?

[OzGav]

Are you using the beta as MP4 tag parsing was just added