I'm having trouble viewing previously imported videos in Lightroom 5.7.1. I'm working on a Macbook Pro (OS 10.11.6). Earlier this month I had no problem reviewing my videos, but that changed all of a sudden last night. The videos are either in a .mov or .avi format. From the time when I could view the videos to now I haven't (knowingly) made any changes to Lightroom 5. My only activity has been to review previously imported photos and videos and delete unwanted ones.
Working in Library module, I double-click the video to enter the Loupe view, but what comes up is a grayed-out box which does have the 'play' button, which, of course, doesn't work. Across the top of the gray box I've seen various messages, such as 'there was an error working with the video.' When I switch to the Develop module, the message is 'video not supported in Develop.'
When I move to Grid view in the Library module, the first image of the video is displayed, but all I get is a revolving 'circle,' which runs continuously, but never actually starts the video.
Would appreciate hearing any thoughts or suggestions on what might be going on.