I think it'd be really cool if Cobalt let you choose a start and end timestamp for what you want to download. I'm not sure if it'd be possible, but it'd save a lot of time.
I know the YouTube Clips feature has already been suggested, but this would ideally work for audio or video from any website. It should detect the length of the video/audio, let you pick a start and end timestamp within that range, and only download the content from between those points.

Of course, you could just download the full video and use an editing program to extract the specific clip you want. That can be very cumbersome, though, especially if the original video is very long, as it will take a long time to download and process the entire thing. That's why I think having an option like this as a part of Cobalt itself would be super helpful and convenient.

I've included a couple of mockups to hopefully better illustrate what I'm trying to say. The playheads on the timeline would be draggable but the user would also be able to input specific time values if they wish. No idea if the previews would be possible but it'd probably make this feature 10x better.