Bug 1483703 - part2 : add telemetry for the media which was blocked before loading metadata and ended up being without audio track. r=cpearce,francois

Add two telemetry scarlar,

"MEDIA_BLOCKED_NO_METADATA" records how many media which was blocked because it hadn't loaded metadata yet.
"MEDIA_BLOCKED_NO_METADATA_ENDUP_NO_AUDIO_TRACK" records how many media which was blocked because it hadn't loaded metadata and ended up for being no audio track.

By collecting those data, we can know the proportion of media which should be autoplay but was blocked because of lacking metadata.

Differential Revision: https://phabricator.services.mozilla.com/D3671

--HG--
extra : moz-landing-system : lando

dom/html/HTMLMediaElement.cpp

@@ -1826,6 +1826,7 @@ HTMLMediaElement::AbortExistingLoads()
   mPendingEncryptedInitData.Reset();
   mWaitingForKey = NOT_WAITING_FOR_KEY;
   mSourcePointer = nullptr;
+  mBlockedAsWithoutMetadata = false;
 
   mTags = nullptr;
   mAudioTrackSilenceStartedTime = 0.0;
@@ -4038,7 +4039,7 @@ HTMLMediaElement::AudioChannelAgentDelayingPlayback()
 }
 
 void
-HTMLMediaElement::UpdateHadAudibleAutoplayState() const
+HTMLMediaElement::UpdateHadAudibleAutoplayState()
 {
   // If we're audible, and autoplaying...
   if ((Volume() > 0.0 && !Muted()) &&
@@ -4047,6 +4048,10 @@ HTMLMediaElement::UpdateHadAudibleAutoplayState() const
     if (AutoplayPolicy::WouldBeAllowedToPlayIfAutoplayDisabled(*this)) {
       ScalarAdd(Telemetry::ScalarID::MEDIA_AUTOPLAY_WOULD_BE_ALLOWED_COUNT, 1);
     } else {
+      if (mReadyState < HAVE_METADATA) {
+        mBlockedAsWithoutMetadata = true;
+        ScalarAdd(Telemetry::ScalarID::MEDIA_BLOCKED_NO_METADATA, 1);
+      }
       if (mReadyState >= HAVE_METADATA && !HasAudio()) {
         ScalarAdd(Telemetry::ScalarID::MEDIA_BLOCKED_AUTOPLAY_NO_AUDIO_TRACK_COUNT, 1);
       }
@@ -5575,6 +5580,12 @@ HTMLMediaElement::MetadataLoaded(const MediaInfo* aInfo,
       (Volume() != 0 && !Muted())) {
     ScalarAdd(Telemetry::ScalarID::MEDIA_BLOCKED_AUTOPLAY_NO_AUDIO_TRACK_COUNT, 1);
   }
+
+  if (mBlockedAsWithoutMetadata && !HasAudio()) {
+    mBlockedAsWithoutMetadata = false;
+    ScalarAdd(Telemetry::ScalarID::MEDIA_BLOCKED_NO_METADATA_ENDUP_NO_AUDIO_TRACK, 1);
+  }
+
   if (mDecoder && mDecoder->IsTransportSeekable() &&
       mDecoder->IsMediaSeekable()) {
     ProcessMediaFragmentURI();

dom/html/HTMLMediaElement.h

@@ -1761,6 +1761,9 @@ protected:
   // before attaching to the DOM tree.
   bool mUnboundFromTree = false;
 
+  // True if the autoplay media was blocked because it hadn't loaded metadata yet.
+  bool mBlockedAsWithoutMetadata = false;
+
 public:
   // Helper class to measure times for MSE telemetry stats
   class TimeDurationAccumulator
@@ -1814,7 +1817,7 @@ private:
 
   already_AddRefed<PlayPromise> CreatePlayPromise(ErrorResult& aRv) const;
 
-  void UpdateHadAudibleAutoplayState() const;
+  void UpdateHadAudibleAutoplayState();
 
   /**
    * This function is called by AfterSetAttr and OnAttrSetButNotChanged.

toolkit/components/telemetry/Scalars.yaml

@@ -948,6 +948,38 @@ media:
       - main
       - content
 
+  blocked_no_metadata:
+    bug_numbers:
+      - 1483703
+    description: >
+      The number of HTMLMediaElements which we blocked because they hadn't loaded metadata yet.
+    expires: "68"
+    kind: uint
+    notification_emails:
+      - cpearce@mozilla.com
+      - alwu@mozilla.com
+      - nohlmeier@mozilla.com
+    release_channel_collection: opt-in
+    record_in_processes:
+      - main
+      - content
+
+  blocked_no_metadata_endup_no_audio_track:
+    bug_numbers:
+      - 1483703
+    description: >
+      The number of HTMLMediaElements which were blocked because they hadn't loaded metadata yet, but ended up having no audio track.
+    expires: "68"
+    kind: uint
+    notification_emails:
+      - cpearce@mozilla.com
+      - alwu@mozilla.com
+      - nohlmeier@mozilla.com
+    release_channel_collection: opt-in
+    record_in_processes:
+      - main
+      - content
+
 # The following section contains content process base counters.
 dom.contentprocess:
   buildID_mismatch: