--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -91,21 +91,28 @@
 #include "mozilla/dom/VideoTrack.h"
 #include "mozilla/dom/VideoTrackList.h"
 #include "mozilla/dom/TextTrack.h"
 #include "nsIContentPolicy.h"
 #include "mozilla/Telemetry.h"
 #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");
 
 #define LOG(type, msg) MOZ_LOG(gMediaElementLog, type, msg)
 #define LOG_EVENT(type, msg) MOZ_LOG(gMediaElementEventsLog, type, msg)
 
 #include "nsIContentSecurityPolicy.h"
@@ -7451,10 +7458,48 @@ HTMLMediaElement::AsyncRejectSeekDOMProm
     nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction([=] () {
       promise->MaybeReject(NS_ERROR_DOM_ABORT_ERR);
     });
     mAbstractMainThread->Dispatch(r.forget());
     mSeekDOMPromise = nullptr;
   }
 }
 
+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

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -97,16 +97,18 @@ public:
   MOZ_DECLARE_WEAKREFERENCE_TYPENAME(HTMLMediaElement)
 
   CORSMode GetCORSMode() {
     return mCORSMode;
   }
 
   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
    * <source> children are ignored.
    * @param aChannel the channel to use
    * @param aListener returns a stream listener that should receive
    * notifications for the stream
    */

--- a/dom/media/MediaPrefs.h
+++ b/dom/media/MediaPrefs.h
@@ -176,16 +176,18 @@ private:
 #endif
 
 #if defined(MOZ_WIDGET_GTK)
   DECL_MEDIA_PREF("media.rust.mp4parser",                     EnableRustMP4Parser, bool, true);
 #else
   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",
                                                               MediaWarningsAsErrorsStageFrightVsRust, bool, false);
 
 public:
   // Manage the singleton:
   static MediaPrefs& GetSingleton();

--- a/dom/media/fmp4/MP4Decoder.cpp
+++ b/dom/media/fmp4/MP4Decoder.cpp
@@ -176,17 +176,17 @@ MP4Decoder::IsAAC(const nsACString& aMim
 {
   return aMimeType.EqualsLiteral("audio/mp4a-latm");
 }
 
 /* static */
 bool
 MP4Decoder::IsEnabled()
 {
-  return Preferences::GetBool("media.mp4.enabled", true);
+  return MediaPrefs::MP4Enabled();
 }
 
 // sTestH264ExtraData represents the content of the avcC atom found in
 // an AVC1 h264 video. It contains the H264 SPS and PPS NAL.
 // the structure of the avcC atom is as follow:
 // write(0x1);  // version, always 1
 // write(sps[0].data[1]); // profile
 // write(sps[0].data[2]); // compatibility