Add Duration Tag to MP4 Video Files

I'm sorry for not writing in your native language but I just started learning french.

I want to add a tag to mp4 files containing the length of the file.

Windows explorer can display the length of mp4 files but gets very slow. it seems to that its calculated every time I open the folder.

Is there a way to automatically add the Length of the Video to a tag (maby the period Tag in Music or any other reasonable)

Thank you very much so far.

Hello
You can add a duration to a MP4 by using the GoogleTrackDuration tag.
ExifTool -GoogleTrackDuration="120" test.mp4
(120=2minutes)
You can use MyBatch with Metadata++ to do that.
Jean