API changes, most recent first:
+2017-05-15 - xxxxxxxxxx - lavc 57.96.100 - avcodec.h
+ VideoToolbox hardware-accelerated decoding now supports the new hwaccel API,
+ which can create the decoder context and allocate hardware frames automatically.
+ See AVCodecContext.hw_device_ctx and AVCodecContext.hw_frames_ctx.
+
+2017-05-15 - xxxxxxxxxx - lavu 57.63.100 - hwcontext.h
+ Add AV_HWDEVICE_TYPE_VIDEOTOOLBOX and implementation.
+
+2017-xx-xx - xxxxxxx - lavc 57.95.100 / 57.31.0 - avcodec.h
+ Add AVCodecContext.apply_cropping to control whether cropping
+ is handled by libavcodec or the caller.
+
+2017-xx-xx - xxxxxxx - lavu 55.62.100 / 55.30.0 - frame.h
+ Add AVFrame.crop_left/right/top/bottom fields for attaching cropping
+ information to video frames.
+
2017-xx-xx - xxxxxxxxxx
Change av_sha_update(), av_sha512_update() and av_md5_sum()/av_md5_update() length
parameter type to size_t at next major bump.