Local videos do not play properly

Expected behavior

Videos stored locally on the device should play properly.

https://user-images.githubusercontent.com/1405144/132623395-bc805e41-97f2-4879-a795-29c49798d887.mp4

Actual behavior

Videos stored locally on the device do not play properly. The thumbnails do not load on the device and long-pressing the video doesn't play it, just opens a view of what appears to be the first frame.

See https://github.com/wordpress-mobile/WordPress-Android/pull/15285#pullrequestreview-748080406 and https://github.com/wordpress-mobile/WordPress-Android/pull/15285#issuecomment-914930637

https://user-images.githubusercontent.com/506707/132365985-61764cf7-158a-40c9-9501-e4c0dde13133.mp4

Steps to reproduce the behavior

1. Launch app and go to My Site -> Post
2. Add a Video block
3. Select “Choose from device” and long press a thumbnail on the following screen
4. Notice the actual vs expected behavior.

Tested on [Pixel5], Android [11], WPAndroid [18.2-rc-2]

The issue exists in 18.2-rc-2 but not in 16.3. Need to investigate what and when things got changed.

Start at My Site → Post, add a Video block, and follow “Choose from device” to reproduce the thumbnail and long-press playback failures on Pixel 5, Android 11. Compare behavior between WPAndroid 16.3 and 18.2-rc-2, and review the discussion and changes in pull request #15285. Done means local video thumbnails load and long-press opens playable video.