Ex. if a subsection starts at 1:43, the thumbnail would be a screenshot of the video at 1:43.
This doesn't seem possible though. See here and here.
My impression is that YouTube doesn't want people doing this and that it violates their TOS. If not, I'd expect them to make this part of their API, because it'd be easy for them and provide a good amount of value for developers.
Ex. if a subsection starts at 1:43, the thumbnail would be a screenshot of the video at 1:43.
This doesn't seem possible though. See here and here.
My impression is that YouTube doesn't want people doing this and that it violates their TOS. If not, I'd expect them to make this part of their API, because it'd be easy for them and provide a good amount of value for developers.