Blender Git Loki

FFmpeg: Adjust default proxy settings

GOP size and quality are adjusted for h264 codec.

These new values are based on result of benchmark on 9 random files:
https://docs.google.com/spreadsheets/d/1nOyUGjoVWUyhQ2y2lAd8VtFfyaY1wQNGj1krCCNbk7Y/edit?usp=sharing

Reducing quality to 50 reduces proxy filesize by about 2x on average
and has no significant impact on decoding performance.

Increasing GOP size from 2 to 10 also reduces proxy filesize 2x-3x
while scrubbing is only about 8% slower. It is still around 100FPS
with 1920x1080 media.
This is unfortunately about 50% slower than MJPEG, but this can be
improved with `fastdecode` tune applied to libx264 encoder

Quite surprisingly h264 codec presets had little influence on proxy
building performance as well as proxy filesize. So far it looks that
FFmpeg does initialize encoder in different way then Blender.
This applies mot only for presets but for tune and profile libx264
setting.
Once this issue is resolved, performance of proxies may be optimized
further.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D10897