Update Video Encoder and tests for 6 container formats

[Dan-Flores]

This PR updates the round trip test in test_ops.py to support 6 common video container formats with absolute tolerance 2 in the best case, and 55 in the worst case.

Additional changes are made to align with the design in #907:

• Allow FFmpeg to select the best pixel format using avcodec_find_best_pix_fmt_of_list
• Add CRF as an option on the C++ side to enable round trip tests

These are the codecs and pixel formats used by default:

## mov: Using codec: libx264 pixel format: gbrp -> yuv444p

mp4:

Using codec: libx264
pixel format: gbrp -> yuv444p

avi:

Using codec: mpeg4
pixel format: gbrp -> yuv420p

matroska (mkv):

Using codec: libx264
pixel format: gbrp -> yuv444p

webm:

Using codec: libvpx-vp9
pixel format: gbrp -> gbrp

flv:

Using codec: flv
pixel format: gbrp -> yuv420p