I am using Lightroom Classic 9.2 on my Mac (MacOS 10.13).
While importing movies taken with my iPhone, I've noticed that Lightroom often hangs while generating the thumbnails. By "hang," I mean that I can step away for hours and then come back to see that the thumbnails are still blank. If I attempt to continue with the import by clicking "Import," the software says "Importing files..." and stays this way until I force quit with activity monitor. Both the source and destination are located on my internal HD. I've modified the Lightroom preferences to DISABLE "Generate Previews in parallel."
After killing Lightroom, I will get a window titled Import Results and the message "An unknown error has occurred while reading the video file..."
After import failure, I use Activity Monitor to examine "Open Files and Ports" for dynamiclinkmediaserver (DLMS) and can observe that DLMS has an open file handle to one particular media file--even after I've killed Lightroom. I can also see under "Statistics" that none of the primary stats (Threads, System Calls, etc) are changing--another sign that DLMS has hung.
Through a process of elimination, I've determined the DLMS seems to choke on Quicktime movie files (*.MOV) which are shorter than 300 kB. I'm attaching one such file (IMG_0484.MOV, 204 kB) which reliably hangs Lightroom during import.
I would appreciate if you took a look and get back to me.
I'll keep an eye out for short videos and try rename them before i try import as a test i'll report back based on one example far that helped a lot. but I'll need to see it work a few times more before i'm confident.
I'm having the same problem, but not always with short video files , and with videos from various cameras.
Originally I assumed it was all HEVC files that are not supported in windows but it shouldn't take 10-20mins to timeout on a file it can't open. So i suspect a probelm elsewhere. Right now i'm sitting waiting for an import i know will fail and when i goto bed and wake up i'll have the error saying files are not supported etc.