Strange problem with Foobar2000 comments in MKA files

[r0lZ]

I have converted a lot of audio tracks to AAC using Foobar2000. It creates them in a M4A container. (Not sure what M4A is exactly, but apparently, it's some kind of MPEG 4 for audio created by Apple.) Because I don't like much that strange M4A container, I have converted all audio files to MKA (Matroska Audio) with mkvtoolnix, without re-encoding (and unfortunately, I have deleted the original M4A files). So, now, I have stereo AAC streams in MKA containers. So far so good. Then, I have tagged the files with Foobar2000's mass tagger tools, without problem. But there are some errors in the tags, and now I want to fix them... and apparently, it's not possible!

For example, I want to change the tag "Performer", that contains a wrong string. If I type (or import) another string and I click Apply, the original string comes back immediately !

I have even tried to remove the wrong tags completely (by right-clicking the "Performer" header and selecting "Remove" in the Properties window). That seems to work, as the original string disappears. When I click Apply or OK, the string stays empty, so I suppose that the tag has correctly been removed. When I re-open the Properties window, the Performer string is still blank, so it seems that it has been correctly removed. But when I try to insert the new, fixed Performer string... the first string reappears again ! So, obviously, it has not been correctly deleted, and it is still impossible to modify it.

Of course, I have verified the files on disc, and they are not read-only or protected by any means.

I have never noticed such strange problems with the tags created by Foobar2000, but 99% of my audio files are in FLAC, OGG or MP3 format. The problem affects obviously only the MKA files.

Someone has already noticed that strange behaviour with Foobar2000 ? Is it a solution to either edit the "not modifiable" tags, or to remove them completely and try again from scratch ?

If it's not possible, perhaps I'll convert the container to the M4A format again, but it's not as easy as converting the M4A to MKA with mkvtoolnox. Apparently, it is possible to re-create the M4A container with MP4Box, but I have not been able to do it. MP4Box doesn't recognise the MKA container. And if I extract the raw AAC stream first, MP4Box recognises it, but it creates empty M4A files of just 1KB.

I would really appreciate if someone can explain how to tag the MKA files successfully, or how to successfully convert from MKA to M4A (with command line tools only, as I have a lot of small files to process).

[Selur]

m4a container = normal mp4 container with m4a mka file name extension (depending on the software it might also contain some itunes specific flags, which are still mp4 compatible)
btw. mka = normal mkv container jsut with mka file name extension
About tagging mkv files: Why not use mkvtoolnix ?

[r0lZ]

Thanks, but mkvtoolnix doesn't permit to tag the MKV/MKA files with all tags supported by Foobar. It is only possible to set the "file title" (not compatible with Foobar and therefore useless for me), and the other tags must be specified using an external XML file. That's not at all convenient, and there is no mass tagger possibilities.

I will try to remux the MKA files to MP4, then change the extension. If that works, that may be a good solution.

Anyway, I want to understand why re-tagging a MKA file that has already been tagged with Foobar doesn't work. Is it a Foobar bug ?

[r0lZ]

OK, it is easy to convert the container from MKA to M4A with ffmpeg, with the command line:
ffmpeg -i input.mka -c:a copy -o output.m4a

The MKA tags are lost during the operation, but it is easy to copy and paste them with Foobar. And luckily, Foobar doesn't have the same bug with M4A files: the wrong tags can be manually edited.

Problem solved.