A codec spec isn't done until there is at least one decoder developed in the field. So reference + 1. The field implementations often become the de facto spec.

Reading the MPEG1 specs back in the 90s as a child opened my eyes to how to define complex systems. For a media coding standard, they spent most of their time saying how to interpret encoded bytes, which I realized is genius. Be descriptive about decoding and you don't have to be prescriptive about encoding. Encoding is where you can apply all the creativity, but you need to provide a way to have a shared understanding of the encoded bytes.