The Palette Definition Segment is documented here, you can is it goes: luminance (y), red (cr), blue (cb), alpha http://blog.thescorpius.com/index.php/2017/07/15/presentation-graphic-stream-sup-files-bluray-subtitle-format/ (I think it's important to be really precise here, because YCbCr is a very common format, so this ordering is slightly unusual: https://en.wikipedia.org/wiki/YCbCr) PiperOrigin-RevId: 350747808
