Tagging script with m4a files


I’ve defined some simple tagging script which saves a tag with some string $set(Test, foobar).

The tagging script is working fine for flac and mp3. Instead for a m4a-file the tag is not written at all. All other standard tags are written correctly.

The custom tag also appears in the tag panel below in Picard for mp3- and flac-files. For m4a-files the custom tag appears together with the standard tags when the album information is loaded by Lookup on the right panel (without any file associated). As soon as an unmatched track is associated to the album the custom tag vanishes from the tag panel and won’t be written to the m4a-file.

It is not related to the kind of custom tag. Behaviour is the same for any custom tag.

OS are macOS or Windows 7 x64, the debug log doesn’t contain any related strings. Anyway it is the same for mp3 and flac. (BTW, any reason why script actions aren’t logged in debug modus?)

Any hint what’s going on?

Picard does currently not support writing unsupported tags to MP4 files. Same is true for ASF ( WMA) files.

Some context: Historically Picard did only write the supported tags to all tagging formats, which had more structured tag names (instead of providing just a plain name value list without further specification on the names, e.g. Vorbis tags). This changed at some point for ID3 tags, but not for MP4 / WMA

I think that should be changed, but we have to look at how other software stores custom tags for MP4 to stay compatible. I assume they store it under the “----:com.apple.iTunes:” namespace. You might want to open a ticket on https://tickets.musicbrainz.org

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Thanks for your quick answer. The fact that Picard writes the standard tags confused me and I didn’t thought it excluded intentionally custom tags.
Your proposal about the namespace is absolutely correct (at least for the 3 programs I know).
Personally I consider custom tags important as for now I have to use 2 applications to write tags to mp4.

I opened a ticket mp4 custom tags not written

Thanks for the ticket. I too consider custom tags as important, especially as Picard gives the impression it does support it :slight_smile:

This is really a change of the mindset in development. In the beginning Picard was supposed to only write the tags it knew about and that were properly supported by the tagging format it wrote to (that means there was some kind of specification or at least there was some tag commonly used by major software), and the tags it knew about where limited to what could be supported. The fact that it wrote everything to e.g. Vorbis tags was more a bug than in feature in this regard.

This has changed over the years, and Picard supports custom tags and also knows about tags it cannot really support itself (but might be used by plugins. And I think there is consensus now that Picard should write all the tags to all file formats, but there this is just not completely implemented.

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See also PICARD-1586.