[Tube8] Fixed video download and added channel download #2971

Job	Run time
Linter	17s
Select tests from inputs	1s
Run tests (ubuntu-20.04, 2.7, cpython, core, sh)	1m 2s
Run tests (ubuntu-20.04, 3.2, cpython, core, sh)	1m 8s
Run tests (ubuntu-20.04, 3.5, cpython, core, sh)	1m 9s
Run tests (ubuntu-20.04, 3.9, cpython, core, sh)	1m 13s
Run tests (ubuntu-20.04, 3.11, cpython, core, sh)	57s
Run tests (ubuntu-20.04, pypy-2.7, cpython, core, sh)	2m 28s
Run tests (ubuntu-20.04, pypy-3.6, cpython, core, sh)	3m 5s
Run tests (ubuntu-20.04, pypy-3.7, cpython, core, sh)	2m 39s
Run tests (windows-2019, 3.4, cpython, core, bat)	1m 59s
Run tests (windows-2019, 3.4, cpython, nodownload, bat)	47s
Run tests (ubuntu-20.04, 2.7, jython, core, sh)	3m 15s
Run tests (ubuntu-20.04, 2.7, jython, nodownload, sh)	28s
	20m 28s

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