Update ffmpeg to 3.2.2 stable and libvpx to 1.6.1

ffmpeg 3.2.2

3.2.2 was released on 2016-12-06. It is the latest stable FFmpeg release from the 3.2.2 release branch, which was cut from master on 2016-10-26.

libvpx 1.6.1
libvpx got some nice improvements lately

https://chromium.googlesource.com/webm/libvpx/+/v1.6.1

2017-01-09 v1.6.1 "Long Tailed Duck"
This release improves upon the VP9 encoder and speeds up the encoding and
decoding processes.

  • Upgrading:
    This release is ABI compatible with 1.6.0.

  • Enhancements:
    Faster VP9 encoding and decoding.
    High bit depth builds now provide similar speed for 8 bit encode and decode
    for x86 targets. Other platforms and higher bit depth improvements are in
    progress.

  • Bug Fixes:
    A variety of fuzzing issues.

We use libvpx master. FFmpeg upgrade is pinned to v3.0.x at the moment until there is time to test a new version, but there are other higher priorities.