Log Message:
libvpx: updated to 1.8.1

v1.8.1 "Orpington Duck"
  This release collects incremental improvements to many aspects of the library.

  - Upgrading:
    VP8E_SET_CPUUSED now accepts values up to 9 for vp9.
    VPX_CTRL_VP9E_SET_MAX_INTER_BITRATE_PCT had a spelling fix (was VP8E).
    The --sdk-path option has been removed. If you were using it to build for
      Android please read build/make/Android.mk for alternatives.
    All PPC optimizations have been disabled:
      https://bugs.chromium.org/p/webm/issues/detail?id=1522.

  - Enhancements:
    Various changes to improve encoder rate control, quality and speed
      for practically every use case.

  - Bug fixes:
    vp9-rtc: Fix color artifacts for speed >= 8.