Bug 1362212 - Implement HTMLMediaElement.reportCanPlayTelemetry. r=gerald

Defer determining whether we have usable decoders to an off-main thread in
order to avoid janking the main thread.

MozReview-Commit-ID: Ape5zEBBMrz

dom/html/HTMLMediaElement.cpp

@@ -96,11 +96,18 @@
 #include "DecoderDoctorDiagnostics.h"
 #include "DecoderTraits.h"
 #include "MediaContainerType.h"
+#include "MP4Decoder.h"
 
 #include "ImageContainer.h"
 #include "nsRange.h"
 #include <algorithm>
 #include <cmath>
+#ifdef XP_WIN
+#include "Objbase.h"
+// Some Windows header defines this, so undef it as it conflicts with our
+// function of the same name.
+#undef GetCurrentTime
+#endif
 
 static mozilla::LazyLogModule gMediaElementLog("nsMediaElement");
 static mozilla::LazyLogModule gMediaElementEventsLog("nsMediaElementEvents");
@@ -7481,5 +7488,43 @@ HTMLMediaElement::AsyncRejectSeekDOMPromiseIfExists()
   }
 }
 
+void
+HTMLMediaElement::ReportCanPlayTelemetry()
+{
+  LOG(LogLevel::Debug, ("%s", __func__));
+
+  RefPtr<nsIThread> thread;
+  nsresult rv = NS_NewNamedThread("MediaTelemetry", getter_AddRefs(thread));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  thread->Dispatch(
+    NS_NewRunnableFunction([thread]() {
+#if XP_WIN
+      // Windows Media Foundation requires MSCOM to be inited.
+      HRESULT hr = CoInitializeEx(0, COINIT_MULTITHREADED);
+      MOZ_ASSERT(hr == S_OK);
+#endif
+      bool aac = MP4Decoder::IsSupportedType(
+        MediaContainerType(MEDIAMIMETYPE("audio/mp4")), nullptr);
+      bool h264 = MP4Decoder::IsSupportedType(
+        MediaContainerType(MEDIAMIMETYPE("video/mp4")), nullptr);
+#if XP_WIN
+      CoUninitialize();
+#endif
+      AbstractThread::MainThread()->Dispatch(
+        NS_NewRunnableFunction([thread, aac, h264]() {
+          LOG(LogLevel::Debug, ("MediaTelemetry aac=%d h264=%d", aac, h264));
+          Telemetry::Accumulate(
+            Telemetry::HistogramID::VIDEO_CAN_CREATE_AAC_DECODER, aac);
+          Telemetry::Accumulate(
+            Telemetry::HistogramID::VIDEO_CAN_CREATE_H264_DECODER, h264);
+          thread->AsyncShutdown();
+        }));
+    }),
+    NS_DISPATCH_NORMAL);
+}
+
 } // namespace dom
 } // namespace mozilla

dom/html/HTMLMediaElement.h

@@ -102,6 +102,8 @@ public:
 
   explicit HTMLMediaElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo);
 
+  void ReportCanPlayTelemetry();
+
   /**
    * This is used when the browser is constructing a video element to play
    * a channel that we've already started loading. The src attribute and

dom/media/MediaPrefs.h

@@ -181,6 +181,8 @@ private:
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, false);
 #endif
 
+  DECL_MEDIA_PREF("media.mp4.enabled",                        MP4Enabled, bool, false);
+
   // Error/warning handling, Decoder Doctor
   DECL_MEDIA_PREF("media.playback.warnings-as-errors",        MediaWarningsAsErrors, bool, false);
   DECL_MEDIA_PREF("media.playback.warnings-as-errors.stagefright-vs-rust",

dom/media/fmp4/MP4Decoder.cpp

@@ -181,7 +181,7 @@ MP4Decoder::IsAAC(const nsACString& aMimeType)
 bool
 MP4Decoder::IsEnabled()
 {
-  return Preferences::GetBool("media.mp4.enabled", true);
+  return MediaPrefs::MP4Enabled();
 }
 
 // sTestH264ExtraData represents the content of the avcC atom found in