Support for asymmetric bit-depth in VP9

[juberti]

Question came up today regarding how asymmetric support for 10-bit should be signaled (i.e., I can produce but not receive 10-bit). Using profile-id doesn't seem like it will work here, but perhaps we could use something like Opus' sprops (e.g. sprop-profile-id?) or max-bit-depth (similar to max-fs/max-fir).

@JonathanLennox @uysalere

[juberti]

ping

[JonathanLennox]

Generally codec negotiation doesn't support asymmetric produce/receive capabilities in terms of fundamental "cannot consume" semantics (as opposed to things like CPU/bandwidth limits). The closest I guess is Opus's sprop- parameters, but even those have the meaning "this isn't useful to me", not "I cannot consume this".

If you can consume 10-bit but it's not useful to you (e.g. you have only an 8-bit display), you could offer both 8-bit and 10-bit profiles as separate codecs, listing the 8-bit one first.