What to do when a function is not supported should be clear

[alvestrand]

There are a number of counters (for example sliCount) that are likely to be:

1. Only implemented for some track types (video in this case)
2. Only implemented by some platforms
   It should be clear what the value of this should be when it's not going to be handled:

• zero always for a platform that does not count them?
• missing for a platform that doesn't count them?
• zero or missing for a track where it's not appliciable? (I think missing)

[vr000m]

1. I think we should clarify that this is for video
2. missing makes most sense. Because 0 has a semantic meaning , i.e., no losses. In XR blocks, we've used 0xff to represent measurement unavailable, but in dictionaries, skipping the key when not measured seems like good advice.

[alvestrand]

Think we should be consistent across all data types - so let it be part of the introduction.

[vr000m]

Special note for jitter as zero has semantic meaning.

[vr000m]

TPAC16 decisions:

“” for strings, 0 and -1 for integers are all legal values under some circumstances.

Proposal:

• Unsupported stats are not present in the dictionary
• Stats that haven’t started counting are present with a suitable starting value
• Special considerations when 0 is a suitable value (such as RTT)!