[X] MP3tag show no tags in M4A after adding replaygain tags

After running the Replaygain function in Musicbee 2.1 on an iTunes M4A file to write Album+Track tags (which I believe just calls AACGain), MP3tag shows the file has no tags or artwork at all. When right clicking a track and selecting properties, in the TAG section of the window MP3tag shows "Version: 0". Subsequently, saving tags in MP3gain will also remove all tags & artwork permanently from the file. There is no issue editing tags in Musicbee, it's only related to running Replaygain.

NOTE: Musicbee continues to see all tags & artwork, as do all my media players (until tags are saved in MP3tag). MP3tag for some reason does not. I acknowledge the problem may not be MP3tag, but since other programs see tags where MP3tag doesn't, I thought I should start here.

edit: Both MP3tag versions 2.56 and 2.57 show show this issue.

Are you using files from the itunes store?
It seems the RG process is setting all the private data fields (catalog id, purchase id,..) to empty values which is a problem for Mp3tag on the catalog id field.
Not sure if this emptying is done on purpose and why it doesn't completely remove the fields.
You should ask what the musicbee replaygain actually does.

Hi. Yes, from the iTunes store. I have no knowledge of the inner workings of Musicbee so I will start a bug report in their forum with your theory and then provide a link to here. Hopefully we can get the author(s) of Musicbee to participate. Thank you!

Edit- Link to Musicbee bug report: http://getmusicbee.com/forum/index.php?topic=10692.0

dano has sent me one of the affected files for further analysis and it seems that the cnID atom has indeed no data -- while it is defined as containing a 32-bit integer.

Instead of corrupting unknown atoms by removing their content, it would be better if MusciBee would simply ignore/preserve them.

Kind regards
Florian

I've added a workaround for this broken MP4 writer with Mp3tag v2.58.

Thank you Florian.

There is another challenge with AAC Gain, since it writes the undo data in the M4A header as a "Free-form metadata tag." Is this data visible to MP3Tag?

The reason I ask is because I use MP3Tag to verify the MP3Gain tags are present in MP3 files by looking for the APEv2 tag in the "Tags" field.

Is there a way to create a column view that shows this undo data for M4A files?

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