P: Videos don't play and don't import

Same to me, in Lightroom Classic i am not able to import new video files or play my previous imported video files. 
I am still able to view videos in my old lightroom version (from 2017, version "2015.12"). 
I tried deleting the cache, but after 5 minutes it not finished so i clicked on "cancel" and nothing happened. So had to kill Lightroom using the task manager. 
Deleting the cache manually (using windows explorer) did not help either.

My problem is similar. LR CC 7 Classic will not import or play video files. Nor will LR 5.7 or Photoshop CC. This is a recent problem. Thumbnails of videos previously imported show in the Catalog. Moving the cursor over the thumbnails produces movement approximating the content of the video file. Double clicking the thumbnail results in the movie play bar appearing but it does not respond to mouse clicks. Typical error messages when trying to import are “An unknown error has occurred while reading the video file. Connecting to Dynamic Link server failed. (1)     F:\My Photos\3-11-2017\MAH00212.MP4” and “There is a problem with the video file (1)     F:\ Photos and Videos\Video Camera Files\00020.MTS  “ and “dynamiclinkmediaserver has encountered an  error [..\..\Src\DirectoryRegistry.cpp-283]”. The import preview thumbnails are blank.

 Solutions tried include uninstalling LR. Using Adobe Cleanup tool and then re-installing. Cleaning the Registry (Win 10). Installing K-Light Codec Pack. Uninstalling same. Purging video cache thru’ LR. Manually deleting contents of video cache. Opening a video file with LR. Uninstalling and re-installing Quicktime. Using Photoshop CC to try and open video file (PS displays “Reading Video Format” before freezing completely). All video files play on other apps e.g VLC player and Quicktime.

Driving me crackers!

I can still play videos in Quick time. What a PITA

Dan, I need your luck. I just purged my video cache, closed Lightroom Classic, restarted my Mac, opened Classic, and still videos won’t play.

So some magic happened while I was out for the last couple of hours. I shut down LR CC Classic without backing up the catalogue and went out on an errand, When I returned I fired up the new Photoshop CC 2018 to test if it would play my  videos which it did without a hitch. I closed Photoshop & reopened Lightroom CC Classic. This time it played successfully all of my video files that I tried. I assume the process of shutting down without saving or backing up & restarting reset a cache or buffer or something.  I had used the new LR yesterday for a couple of hours testing on dng files & shutdown as I normally would with a backup.  I don't like mysteries but at least it seems to be working for now.  I hope this helps others with this problem.

Have you tried manually deleting the medica cache, as described in the link above?

I agree and have the same problem as Dan. This should have been addressed before Classic was released!

I just installed the new Lightroom CC Classic on macOS Sierra and now cannot play video files. The files are not corrupt as they play fine in Quicktime.  It's ridiculous that a problem like this should occur in a new release of Lightroom!

Mark, you should  click ME TOO in the upper-right corner to add your vote.  Adobe generally reads every topic here, but they pay most attention to those that have more votes.

The link I posted above contains the locations of the media cache on Mac and Windows: https://forums.adobe.com/message/7553521#7553521 . Deleting it helped Wolfgang, maybe it will help you.

John, I am having the same problem as Stefan and Wolfgang. My videos from "old" Lightroom CC were imported into Lightroom Classic. I can see the videos are in the thumbnails but when I try to play, I get the same error message as others. Video won't play and can't be imported into Lightroom Classic. I do not know what the video cache is or where it can be found, but if I delete it? will Lightroom Classic than play and import videos? Why didn't Adobe adress this problem before Lightroom Classic release? Also, are they aware of the problem now? Thanks for all you help.