MP4/M4V not supported?

I am trying to tag some music videos, which are in M4V or MP4 format. I used to do the same before, which worked. Somehow, this no longer appears to be supported. Any idea what I am doing wrong?

After scanning, the songs show with a red mark. Below the error log:

E: 23:19:23 Traceback (most recent call last):
File “picard\util\thread.pyo”, line 46, in run
File “picard\file.pyo”, line 210, in _save_and_rename
File “picard\formats\mp4.pyo”, line 173, in _save
AttributeError: ‘NoneType’ object has no attribute ‘clear’

Thanks for your help!

This is strange and probably a bug. But from looking at the code it looks like your files have currently no tags at all, and Picard fails on that. You might want to disable “clear all existing tags” and try again.

It would be great if you would file a bug on, and if you could make one.of the affected files available somehow.

Thanks for your kind reply. I fixed it by reconverting the files with Handbrake. It is now working, so I assume the issue was with my files and not with Picard.

There is a related long-standing issues though about MP4/M4V tags. Let me know if you or someone else could have a look and I am happy to provide sample files or additional context:

Artists/Albumartists tags not supported for MP4/M4V