Improve Codec Arguments

[WoofinaS]

This Merge request makes the following changes

x264

• Increased preset from medium to slow
• Uses preset medium's direct argument for minor speed up
• Switched to qp instead of crf to improve generation loss
• Dropped quality level to 16 to avoid obvious artifacts

  x265

• Switched to qp instead of crf to improve generation loss

  AV1

• Dropped down to preset 8 for smaller output size
• Switched to qp instead of crf to improve generation loss

  VP9

• Switched to yuv420p as not all vp9 hardware decoders and software support 10bit

  NVENC

• Dropped down to preset 6 for large speed up and almost no quality loss
• Switched to qp instead of crf to improve generation loss

Overall this should be a negligible performance decrease or in some case performance gain for better quality. This should also fix VP9 playback with some hardware and media players

[mafiosnik777]

thanks a lot!