Some HEVC MKV files have frozen video

Freezes happen either at first frame or within the first 10 seconds. Audio continues to play. QA indicates this might not be taking HW decode path. Example files:

• http://demo-uhd3d.com/fiche.php?cat=uhd&id=21
• http://trailers.divx.com/hevc/TearsOfSteel_4K_24fps_9500kbps_2aud_9subs.mkv.

Internal BugID: 200299573