OAuth access token lifespan

My application retrieves information about a user’s channel after the user has seen the permissions dialog with the scope list and approved the request. The OAuth access tokens I’ve been getting have had lifespans of about four hours. Once that four hours has passed, is it still possible to refresh the access token?

If not, will the user, once again, need to view the permissions dialog and personally approve for the application to acquire another valid access token and resume functioning?

Yes, use the refresh_token you got when you got the original token to get a new token.

Access Tokens has a timespan, currently, refresh tokens do not have an expiration