Edit audio tags in mp4 container

[thinredline]

Hello.
I have an mp4 file which contains 5 audio tracks in FLAC.
I don't know how can I edit the tags of these tracks, so that I can add a description for each one.
I have tried mp3tag, and MP4 Video & Audio Tag Editor, but I cannot find how they work.
Any easy software that I can do this?

[ProWo]

Use clever Ffmpeg-GUI.
Load your mp4, click main page, click multiplex.
Here you can enter language code and title for each stream.
Then set mp4 as container and click multiplex.
Done.

[thinredline]

Use clever Ffmpeg-GUI.
Load your mp4, click main page, click multiplex.
Here you can enter language code and title for each stream.
Then set mp4 as container and click multiplex.
Done.

Thanks. It doesn't do any re-encoding of the video/audio, right?
Because I don't want that.

EDIT: By the way, I downloaded ffmpeg which was required, and although I find the bin file in the start of the software, i get this message:


[Attachment 87689 - Click to enlarge]

I have Windows 10 64bit.

EDIT2: OK, I downloaded the ffmpeg from the link that it was in the Readme file of your software, and now it opens fine.

[ProWo]

It doesn't do any re-encoding of the video/audio, right?
Because I don't want that.

No, no re-encode, only mux (stream copy).

[thinredline]

No, no re-encode, only mux (stream copy).

Ok, I did it, but I cannot play the resulting file.
It shows me this:

[Attachment 87690 - Click to enlarge]

What did I do wrong?

edit: Ok, now it plays. I don't understand.