Generating video thumbnails is very slow when using multithread

I know we have multithread settings when gen thumbnails, it performs well for pictures.
But for videos, with multithread setting to >1, when you open a directory with many videos, the genearation becomes very show and some videos' thumb would never show. But it performs normally with multithread setting to =1. I reproduced the bug in different scenarios.

BTW, can we have an extra option for multithread especially of HDD? Because for HDD, multithread will reduce the performance instead of improving. It prefers being read sequentially.

BTW again, can we also have an extra option for not generating thumbs for network drive?

Is it the same whether or not the Movie viewer plugin is enabled?

Movie thumbnails usually come via Windows these days, and we saw a bug in Windows 10 which affected both Opus and File Explorer if things requested folder thumbnails on multiple threads.

We added some protection against that (as much as we can; we can't control how many threads any other program uses) for folder thumbnails, but maybe we need to do the same for all thumbnails that come via Windows. That would also solve your other issues, if they're only with movie files.

Thanks for your reply. On my computer, when setting movie plugin to process thumb, it seems even a little slower.
Also, it doesn't help disabling movie plugin.

I uploaded 100 small videos for you to test:
https://aeveaverv.s3.us-west-1.amazonaws.com/Temp1.rar

If it cannot be solved now, can we mitigate it by using single thread when processing video files?

We'll have a change for this in the next beta.

After some investigation, the Windows shell is completely unreliable if more than one thread asks it for a thumbnail at once, whether it's a thumbnail for a folder (which we already knew about) or a video file (which we didn't realise until now). It'll start saying it can't generate thumbnails for things when it can.

Unfortunately, this also applies when other programs happen to be asking at the same time, so it's impossible to fix it completely. But we'll make a change so that Opus only asks the shell for one thumbnail at a time, so that it doesn't cause problems for itself.