Add casts when converting from int64_t or double to int32_t

This fixes warnings when building with MSVC.
Merge pull request #1597 from mstorsjo/msvc-casts

Add casts when converting from int64_t or double to int32_t
Add subSPS pre-active check in CheckActiveSPS
Merge pull request #1599 from HaiboZhu/Debug_Add_subSPS_check

Add subSPS pre-active check in CheckActiveSPS
add a decoder status: float fActualAverageFrameSpeedInMs;          ///< actual average_Decoding_Time, includeing freezed picture
Merge pull request #1601 from dongzha/FixDecodeStatusFps

add a decoder status: float fActualAverageFrameSpeedInMs
fix decoderstatus ecratio bug