x265: detect X265_BUILD

As the library symbols are suffixed with the exact build version, and
it is not clear yet whether the API will be broken or simply extended,
watch for the exact version number (which is 1)
x265: initialize picture and set picture type
contrib: vpx: update to 1.2.0
flac packetizer: use the largest possible frame size

Fixes #6476
Fixes #9442
avcodec: on audio encode, sync timestamps more often from input

Ref #9022
avcodec: map AV_NOPTS_VALUE and VLC_TS_INVALID
httplive: small simplification
avcodec: remove AV_NOPTS_VALUE cast

AV_NOPTS_VALUE already contains a cast to int64_t