Stat for adaptation reason

[henbos]

The resolution of a video track can adapt due to network or cpu limitations. It would be useful to have a stat to say if the framesWidth or framesHeight changed due to reasons of cpu, network or both.

This can be achieved with a bitmask or several booleans.

[henbos]

@alvestrand Is frameWidth/frameHeight the pre- or post degradation resolution? Spec says "represents the width of the video frame for this track".

[alvestrand]

Is there a bitmask WebIDL type?
I'd prefer to stay away from things like "1 means A, 2 means B, 4 means C", so I'd rather have booleans.

frameWidth / frameHeight should be the "native resolution" you get if you connect that track to a

[henbos]

Should we add actual video quality resolution as well? You probably know the size of the element already, but when you're gathering stats you want to know the current quality, no?

[alvestrand]

the

[henbos]

+@vr000m What is preferred if we don't have a bitmask, a boolean member for each option (adaptionReasonCpu, adaptionReasonNetwork) or a sequence of strings or sequence of enum (adaptionReasons with "cpu" and "network")?

[henbos]

Related: Chromium's non-spec compliant version of getStats currently has:

ssrc.googBandwidthLimitedResolution
ssrc.googCpuLimitedResolution

[henbos]

What does CPU limited mean?

[vr000m]

My question here is what does it mean to be Bandwidth and CPU limited?

And if I prefer to not change the Resolution in the degradation preference and it decreases, does this help me?

[icydragons]

There also was googViewLimitedResolution at some point, not sure what happened to it.

I agree with either booleans or a repeated enum field. Bitmap is likely the most concise, but it also is less readable or understandable. I could definitely see additional values being added to this either by chrome or by another webrtc implementation.

[alvestrand]

Alternatives:

1. sequence (enum) - "CPU", "Bandwidth", "other".
2. Pick the one that's obvious - "None", "CPU", "Bandwidth", "other"

[alvestrand]

Observation is "adaptation is happening".
Stat is "platform's specified reason(s) for the adaptation".
Question: Can there be different reasons for resolution adaptation and framerate adaptation? Probably not.
Don't overthink it - it's a hint, not a deep-level diagnostic.

[vr000m]

no meaning to the order of events.

[henbos]

To be continued at #256