Adjusting a video duration

 Hi everyone,

I have a mp4 Video but I would like to adjust its duration. I followed the hints on how to trim the videos (OPTIONS->Edit Video->Trim). I am able to adjust the duration but when I click on "Save & Close" the following message appears:

I tried various Videos and the message is always the same.

Any idea on what I am doing wrong?

Thank you in advance for any clue.

 

best regards,

Karolina