video: Our implementation of ITU-R BT2020 might be incomplete
Report ITU-R BT.2246-8 makes the distinction between constant luminance BT2020 and non-constant luminance BT2020. Although the matrix parameters are the same (iiuc), the order of operations might differ.
For instance the kernel defines enums for both, see https://www.kernel.org/doc/html/v6.6/userspace-api/media/v4l/colorspaces-defs.html?highlight=v4l2_ycbcr_enc_bt2020#id3
We should also clarify our docs about this.