Merge pull request #14339 from huchengtw-moz/video/Bug_945508_bad_playback_layout

Bug 945508 - WebM video with 11:9 aspect ratio has bad playback layout, r=djf
(cherry picked from commit 9a1e5fee6d68d7124ce84ce6b96dc63d73ad9085)
Merge pull request #14734 from huchengtw-moz/video/Bug_945508_v1.3

Merge pull request #14339 from huchengtw-moz/video/Bug_945508_bad_playba...