http urls redirect to them.
When `-f` is not specified it's misleading to see `You have requested ...` as user did not actually request any formats.
Unfinished
[CBSNewsIE] Relax thumbnail regex so test passes
_extract_urls
We ignore them instead of failing to match the behaviour of the 'playliststart' parameter.
It uses the same method as YoutubeSubscriptionsIE, if other feed starts using it we should consider using base class.
Idea: "puncture" some consecutive fragments and check whether the b64decode result of a punctured string is a valid JSON or not. It's a O(N^3) algorithm, but should be fast for a small N (less than 30 fragments in all test cases)
Looks like final download links can expire before downloading process reach them. So, resolving download links right before actual downloading.