I'm constantly having to create thumbnails for Youtube, is there a way to take the finished Video from within Sony Vegas Pro 13 and grab a thumbnail from any timeline?
First use the icon above the preview window to set preview quality to full (best) to obtain highest resolution result. Then with the cursor on the desired location on the timeline, use the icon above the preview window to copy snapshot to clipboard. After you have done this you may want to set your preview quality back to a lower setting if needed for smooth previewing.
There was a change in the behaviour of these commands in VP9.0. If you use Auto quality then there is no need to change to Best.
Copy Snapshot to Clipboard and Save Snapshot to File now deinterlace interlaced images and operate at Best (Full) resolution if the Video Preview is set to (Auto) size and Good quality if set to Draft or Preview.
IMO it would now be better if it changed to Best in every case.