add framesDropped stats to video sender(RTCOutboundRtpStreamStats)

[bdrtc]

video frame maybe dropped prior to encode, according to webrtc code
the capture video frame maybe dropped by encoder's internal rate limiter or MediaOptimizations , but no stats about this now, its useful for diagnose online video problems, and the same stats exist in[RTCInboundRtpStreamStats.
we recommend add such stats to video sender side.

[lidp888]

we add this in native code, add get via getStas, report to our diagnostic system for analize online user rtc problem.

[henbos]

I think you can look at the delta between media-source.frames and outbound-rtp.framesEncoded

[vr000m]

inputFrames and framesEncoded should give you this.

[bdrtc]

yes, user can calculate this via exist stats, but it leave complex to end user, the same stats exist in RTCInboundRtpStreamStats, but not exist in RTCOutboundRtpStreamStats, user may confused.

[vr000m]

framesDiscardedBeforeSend is that the metric that you need? in this case, we should put it in to provisional-stats, unless this is going to be exposed by the browsers.

[henbos]

libwebrtc has 185 implemented metrics (or 213 if you include some deprecated ones; 232 if you also include some that are not exposed to JavaScript). So as much as I like convenience, I'm opposed to adding metrics that are equivalent to "X - Y" of already exposed metrics.

[bdrtc]

framesDiscardedBeforeSend is that the metric that you need? in this case, we should put it in to provisional-stats, unless this is going to be exposed by the browsers.

not necessary，user want get it via getStats and report to a diagnostic system, we can get it via what @henbos described.

[henbos]

👍