Support reading video from url

[dreamerlin]

No description provided.

[codecov]

Codecov Report

Merging #531 into master will decrease coverage by 0.06%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master     #531      +/-   ##
==========================================
- Coverage   64.64%   64.58%   -0.07%     
==========================================
  Files         131      131              
  Lines        7462     7503      +41     
  Branches     1317     1328      +11     
==========================================
+ Hits         4824     4846      +22     
- Misses       2395     2411      +16     
- Partials      243      246       +3     

Flag	Coverage Δ
#unittests	64.58% <55.55%> (-0.07%)	⬇️

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Impacted Files	Coverage Δ
mmcv/fileio/handlers/json_handler.py	70.00% <0.00%> (-7.78%)	⬇️
mmcv/image/__init__.py	100.00% <ø> (ø)
mmcv/runner/checkpoint.py	67.34% <11.76%> (-5.28%)	⬇️
mmcv/image/geometric.py	94.47% <90.90%> (-0.48%)	⬇️
mmcv/version.py	92.30% <100.00%> (ø)
mmcv/video/io.py	91.41% <100.00%> (+0.05%)	⬆️

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