Mp3tag supports two tag formats for MP4/M4A/M4B: iTunes/QuickTime and Nero metadata.
When writing metadata, Mp3tag tries to only use iTunes/QuickTime metadata if possible, but writes Nero metadata in the following circumstances:
-
The file already contains Nero metadata. Mp3tag then updates both metadata formats with the updated contents.
-
The file contains QuickTime chapters. Mp3tag can't edit QuickTime chapters at the moment — only reading and removing QuickTime chapters is supported. On writing, Mp3tag creates a copy of the existing chapter data as Nero chapters. These chapters are used at further edits, which also implies that the original QuickTime chapters can contain outdated data.
-
The file needs to be updated with cover data that's not supported by iTunes/QuickTime metadata. That is, any cover type other than
FrontorOther.
When reading metadata from MP4 files, Mp3tag prioritizes Nero tags. This means that if you modify metadata outside of Mp3tag (e.g., via Windows Explorer or mutagen) and the external tool only supports iTunes/QuickTime metadata, you won't see the modified values in Mp3tag.
If you want to remove Nero metadata, you can use AtomicParsley with the follwing command line
AtomicParsley YOUR_FILE.M4A --overWrite --manualAtomRemove moov.udta.chpl --manualAtomRemove moov.udta.tags
If you have further questions or need support regarding MP4 metadata, please open a separate topic referencing this topic.