VP9

• webm wiki: VP9 Encoding Guide
• FFmpeg and VP9 Encoding Guide
• ffmpeg libvpx documentation
• VP9 Bitrate Modes in Detail - Google's
• AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part I - Lossless - a good read, I like this one
• Pitfalls in VP9 - goes in a bit of detail about quality levels
• VP9 Tips - Encoding Modes and Recommended Command Line Options - upstream's wiki

By default, vpxenc will use two-pass method for encoding.

By default, HandBrake uses a CQ of 22.