Add UMA to record encryption scheme used by HTML5 video

Record the encryption scheme reported in the video for both the audio and
video streams. Reported when the first AudioDecoderConfig/VideoDecoderConfig
is seen for the file.

BUG=658026
TEST=tested locally

Change-Id: Id210e18f0cedc11800abdce5286eb8488271516a
Reviewed-on: https://chromium-review.googlesource.com/1038784Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558897}

media/blink/webmediaplayer_impl.cc

@@ -33,6 +33,7 @@
 #include "media/audio/null_audio_sink.h"
 #include "media/base/bind_to_current_loop.h"
 #include "media/base/cdm_context.h"
+#include "media/base/encryption_scheme.h"
 #include "media/base/limits.h"
 #include "media/base/media_content_type.h"
 #include "media/base/media_log.h"
@@ -168,6 +169,21 @@ blink::WebLocalizedString::Name GetSwitchToLocalMessage(
   return blink::WebLocalizedString::kMediaRemotingStopNoText;
 }
 
+// These values are persisted to UMA. Entries should not be renumbered and
+// numeric values should never be reused.
+// TODO(crbug.com/825041): This should use EncryptionMode when kUnencrypted
+// removed.
+enum class EncryptionSchemeUMA { kCenc = 0, kCbcs = 1, kCount };
+
+EncryptionSchemeUMA DetermineEncryptionSchemeUMAValue(
+    const EncryptionScheme& encryption_scheme) {
+  if (encryption_scheme.mode() == EncryptionScheme::CIPHER_MODE_AES_CBC)
+    return EncryptionSchemeUMA::kCbcs;
+
+  DCHECK_EQ(encryption_scheme.mode(), EncryptionScheme::CIPHER_MODE_AES_CTR);
+  return EncryptionSchemeUMA::kCenc;
+}
+
 }  // namespace
 
 class BufferedDataSourceHostImpl;
@@ -1595,7 +1611,15 @@ void WebMediaPlayerImpl::OnMetadata(PipelineMetadata metadata) {
                             metadata.video_decoder_config.video_rotation(),
                             VIDEO_ROTATION_MAX + 1);
 
+  if (HasAudio()) {
+    RecordEncryptionScheme("Audio",
+                           metadata.audio_decoder_config.encryption_scheme());
+  }
+
   if (HasVideo()) {
+    RecordEncryptionScheme("Video",
+                           metadata.video_decoder_config.encryption_scheme());
+
     if (overlay_enabled_) {
       // SurfaceView doesn't support rotated video, so transition back if
       // the video is now rotated.  If |always_enable_overlays_|, we keep the
@@ -3187,4 +3211,19 @@ void WebMediaPlayerImpl::RecordTimingUMA(const std::string& key,
     base::UmaHistogramMediumTimes(key + ".EME", elapsed);
 }
 
+void WebMediaPlayerImpl::RecordEncryptionScheme(
+    const std::string& stream_name,
+    const EncryptionScheme& encryption_scheme) {
+  DCHECK(stream_name == "Audio" || stream_name == "Video");
+
+  // If the stream is not encrypted, don't record it.
+  if (encryption_scheme.mode() == EncryptionScheme::CIPHER_MODE_UNENCRYPTED)
+    return;
+
+  base::UmaHistogramEnumeration(
+      "Media.EME.EncryptionScheme.Initial." + stream_name,
+      DetermineEncryptionSchemeUMAValue(encryption_scheme),
+      EncryptionSchemeUMA::kCount);
+}
+
 }  // namespace media

media/blink/webmediaplayer_impl.h

@@ -77,6 +77,7 @@ class GLES2Interface;
 namespace media {
 class CdmContextRef;
 class ChunkDemuxer;
+class EncryptionScheme;
 class VideoDecodeStatsReporter;
 class MediaLog;
 class UrlIndex;
@@ -574,6 +575,11 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   // of |chunk_demuxer_|, while the EME one is only recorded if |is_encrypted_|.
   void RecordTimingUMA(const std::string& key, base::TimeDelta elapsed);
 
+  // Records the encryption scheme used by the stream |stream_name|. This is
+  // only recorded when metadata is available.
+  void RecordEncryptionScheme(const std::string& stream_name,
+                              const EncryptionScheme& encryption_scheme);
+
   blink::WebLocalFrame* const frame_;
 
   // The playback state last reported to |delegate_|, to avoid setting duplicate

tools/metrics/histograms/enums.xml

@@ -29522,6 +29522,11 @@ Called by update_use_counter_css.py.-->
   <int value="21" label="Gesture requirement overridden by play method."/>
 </enum>
 
+<enum name="MediaEncryptionScheme">
+  <int value="0" label="CENC"/>
+  <int value="1" label="CBCS"/>
+</enum>
+
 <enum name="MediaEngagementClearReason">
   <int value="0" label="Data (all)"/>
   <int value="1" label="Data (range)"/>

tools/metrics/histograms/histograms.xml

@@ -37291,6 +37291,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.EME.EncryptionScheme.Initial.Audio"
+    units="MediaEncryptionScheme">
+  <owner>jrummell@chromium.org</owner>
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    The encryption scheme used by the audio stream in an HTML5 video. Reported
+    when metadata is available if the initial config is encrypted.
+  </summary>
+</histogram>
+
+<histogram name="Media.EME.EncryptionScheme.Initial.Video"
+    units="MediaEncryptionScheme">
+  <owner>jrummell@chromium.org</owner>
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    The encryption scheme used by the video stream in an HTML5 video. Reported
+    when metadata is available if the initial config is encrypted.
+  </summary>
+</histogram>
+
 <histogram base="true" name="Media.EME.generateKeyRequest"
     enum="MediaKeyException">
   <obsolete>