RTCVideoSourceStats.framesPerSecond should be a double

[dontcallmedom]

All the fields framesPerSecond as defined as double except in RTCVideoSourceStats where it is defined as an unsigned long.

[alvestrand]

Wonder if we did this right. The definitional text for these entries says that it's a count, not a calculation ("number of frames ... in the last second").
Implementation has it somewhat approximate, though, so double may be more fitting.

Suggest to leave it as is, but wanted to record the doubt.

[bc-lee]

This is not only a problem with RTCVideoSourceStats.framesPerSecond, but also with RTCInboundRtpStreamStats, RTCOutboundRtpStreamStats.
hbos already asked how FPS is calculated when the two words "last second" were introduced at #209.

[vr000m]

I think the intention of the metric to return the latest Or current FPS for frames received in the last second.

Much like round trip time, which also returns the latest RTT measurements.

So this is invariant to how often you call getStats, it would always return the current value.

Otherwise, I'd recommend that we use the delta of framesSent and/or framesDecoded between two getStats API calls to calculate that interval's FPS.