This will be something for the developer of the software you are dragging the file into to investigate as Start11 is not involved in that process at all.  It will do exactly the same if you dragged from an explorer window directly to the app window rather than via the taskbar.

I would suspect you lack some codec support somewhere.

Hello,

Sorry to hear you are having issues.

I work with MP4 video / editing programs daily with no issues 

I also use this codec pack from KLite https://codecguide.com/download_k-lite_codec_pack_mega.htm

Also your video editing program could be at fault , I would re install it .

That might help also .

What video editing program are you using , I use several different ones my self .

AzDude
Stardock Community Assistant

OK, just to be thorough:  i installed the icon pack.  I rebooted.  I launched the video editor.  When I tried to pin it to the app on the taskbar, the attributes told me it could go through the taskbar as an audio clip.  So then i did the import directly to the bid3eo editor timeline and that was recognized as an MP4 video.  So that worked.  But if your expectation would be that I could drag from file to taskbar to the app icon, that did not work.  But I am good at this point.  Thanks!