Need to include "libwinpthread-1.dll" in MinGW Windows packages.
Don't return decoded pictures when prerolling.
(cherry picked from commit 12266980b808ab16658172d0e027315130911acf)
Don't try to decode on "BLOCK_FLAG_DISCONTINUITY".
(cherry picked from commit d3a20edefa83f1875564de9112254bed9b438508)
Skip frames if computer is too slow for decoding.
(cherry picked from commit 00b02d1442c7bbc03d925346813700de42be68b6)