Adding support for HEVC video codec

[KarlGallagher]

Using same FFmpeg parameters as h264 for the most part but letting the encoder choose profile and level automatically. Bitrate settings mirror vp9

tested on macOS 10.15.7 and Ubuntu 20.04 LTS (FFmpeg 4.4)

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[KarlGallagher]

@googlebot I signed it!

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[KarlGallagher]

@joeyparrish I think ill have to close and reopen a new PR to resolve issues with my primary email.

@TheModMaker - thanks, will incorporate the suggested changes in the new PR