15a67c0947
Currently, this just functions as a more principled and user-friendly replacement for the (undocumented and hard to use) *_chr_pos fields. However, the goal is to automatically infer these values from the input frames' chroma location, and deprecate the manual use of *_chr_pos altogether. (Indeed, my plans for an swscale replacement will most likely also end up limiting the set of legal chroma locations to those permissible by AVFrame properties)