Log Message:
Update gstreamer1 to 1.12.3

Major bugfixes in 1.12.3

    Fix for infinite recursion on buffer free in v4l2
    Fix for glimagesink crash on macOS when used via autovideosink
    Fix for huge overhead in matroskamux caused by writing one
      Cluster per audio-frame in audio-only streams. Also use
      SimpleBlocks for Opus and other audio codecs, which works around
      a bug in VLC that prevented Opus streams to be played and
      decreases overhead even more
    Fix for flushing seeks in rtpmsrc always causing an error
    Fix for timestamp overflows in calculations in audio encoder base class
    Fix for RTP h265 depayloader marking P-frames as I-frames
    Fix for long connection delays of clients in RTSP server
    Fixes for event handling in queue and queue2 elements, and
      updates to buffering levels on NOT_LINKED streams
    Various fixes to event and buffering handling in decodebin3/playbin3
    Various fixes for memory leaks, deadlocks and crashes in all modules
    ... and many, many more!