[Shotwell] Two Questions about thumbnails

[3×5 <Hi 3x5 co>]

Hi again,

I have two questions about thumbnails:

1. How do I regenerate individual thumbnails? For whatever reason, there are a few places in my library where the thumb is totally wrong and I would like to reset only these thumbs.
   
   I would just go into /thumbs, find the corresponding file name and delete the thumb -- only the file names of the thumbs don't appear to correspond to the filename of the full image.
   
   
2. I read somewhere that because Shotwell uses cutting-edge libraries, thumbnails will often not show up for videos. Am I understanding this correctly? I would like to keep my gstreamer packages synced with Shotwell, if possible, because it really helps to find videos when you can see a thumbnail.
   
   I'm using Shotwell 0.14.1. What do I need to do to get my video thumb functionality? And, once I do this, do I need to manually regenerate thumbs for all my videos?

Thanks so much,
Morgan