How does YouTube report their metric? We should probably just follow their model.

+strobe: See #1. Is dropped_frame/decoded_frame percentage a reasonable metric to collect? Or do you have better suggestions?

ppergame: Any comments on #2?

Hmm, well, we have pretty detailed logs that let us know certain trends, both aggregated and on an individual playback level. For instance, dropped frames are much more common during the start of playback, and (duh) they're more common at the start of playback. This is possible because we report the dropped frame accumulation on a regular basis throughout the playback - at every "interesting event" like a format change, or every thirty seconds.

We don't collect dropped/decoded explicitly, but we do know the framerate of the media that's playing, so we can usually compute it.

dalecurtis: I heard that you plan to add number of decoded/dropped frames to UKM for each playback session. Is that right? If so, I don't think we need to work on this UMA any more. If there's a bug tracking that I can close this one.

Yes, but no bug tracking it yet. 

We have UKM decoded/dropped frames from MediaCapabilities right now, so going to hold off on adding these in for WatchTime just yet. We'll look at this again in Q1 after we've evaluated the value of those UKMs.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/74612b7459881f9194f4d404e4f6688efe0bd8f5

commit 74612b7459881f9194f4d404e4f6688efe0bd8f5
Author: Dale Curtis <dalecurtis@chromium.org>
Date: Thu Dec 14 20:56:19 2017

Plumb UKM PlayerID for WatchTime and VideoDecodeStats recording.

This uses the player ID assigned to every MediaMetricsProvider
per WebMediaPlayerImpl instance to correlate metrics like watch
time, video decoder stats, and more.

A new Media.WebMediaPlayerState UKM event is added which tracks
the player id and final pipeline status. Later on we can add
other one-time lazily-generated metrics like time to first frame,
or time to load, etc.

The player id value is then added to both the existing UKM events
for watch time and decoder stats.

Also later on we can use this to move more of the metrics logged
through MediaInternals today to the metrics provider.

BUG= 706276 , 794263 
TEST=updated unittests.
TBR=bauerb

Change-Id: I59ecad7f858b228f1fddb4eb8215b127e606ca93
Reviewed-on: https://chromium-review.googlesource.com/822168
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524167}
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/chrome/browser/browsing_data/browsing_data_remover_browsertest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/blink/watch_time_reporter_unittest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/blink/webmediaplayer_impl.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/blink/webmediaplayer_impl_unittest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/interfaces/media_metrics_provider.mojom
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/interfaces/watch_time_recorder.mojom
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/BUILD.gn
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/media_metrics_provider.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/media_metrics_provider.h
[add] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/media_metrics_provider_unittest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/video_decode_perf_history.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/video_decode_perf_history.h
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/video_decode_perf_history_unittest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/video_decode_stats_recorder.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/video_decode_stats_recorder.h
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/watch_time_recorder.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/watch_time_recorder.h
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/media/mojo/services/watch_time_recorder_unittest.cc
[modify] https://crrev.com/74612b7459881f9194f4d404e4f6688efe0bd8f5/tools/metrics/ukm/ukm.xml

Tentatively marking as fixed since we can correlate dropped frames from MediaCapabilities reports now with a playback.