Changes in rBce649c73446e, affected established proxy codec preset.
Presets were not working and all presets were similar to `veryfast`.
Tunes are now working too, so `fastdecode` tune can be used. I have
measured little improvement, but I tested this only on 2 machines and
I have been informed that `fastdecode` tune does influence decoding
performance for some users.
Change preset from `slow` to `veryfast` and add tune `fastdecode`
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D11454
a9dfde7b49