Extends timeout for caption extraction.

This is probably not the best way to handle this.. The problem is if the recording file stops growing
for a few seconds we time out. This allows you to extend the timeout with the --endtime parameter and
by default sets the endtime to 1 hour after a recording started (if it is using mythtv naming conventions.)
(cherry picked from commit 0112efc046ebf14780503ee12d36fd9ff9228c3b)