Add UMA stats for OS input glitches on Mac.

media/audio/mac/audio_low_latency_input_mac.cc

Index: media/audio/mac/audio_low_latency_input_mac.cc
diff --git a/media/audio/mac/audio_low_latency_input_mac.cc b/media/audio/mac/audio_low_latency_input_mac.cc
index b945d7ff445af864d4cfc6d0af32bc07577b6046..5eb91ee953922a0f05e23d9f33639675fdc1a952 100644
--- a/media/audio/mac/audio_low_latency_input_mac.cc
+++ b/media/audio/mac/audio_low_latency_input_mac.cc
@@ -127,6 +127,7 @@ AUAudioInputStream::AUAudioInputStream(AudioManagerMac* manager,
                                        AudioDeviceID audio_device_id)
     : manager_(manager),
       number_of_frames_(input_params.frames_per_buffer()),
+      number_of_frames_requested_(0),
       io_buffer_frame_size_(0),
       sink_(nullptr),
       audio_unit_(0),
@@ -140,7 +141,12 @@ AUAudioInputStream::AUAudioInputStream(AudioManagerMac* manager,
       start_was_deferred_(false),
       buffer_size_was_changed_(false),
       audio_unit_render_has_worked_(false),
-      device_listener_is_active_(false) {
+      device_listener_is_active_(false),
+      last_sample_time_(0.0),
+      last_number_of_frames_(0),
+      total_lost_frames_(0),
+      largest_glitch_frames_(0),
+      glitches_detected_(0) {
   DCHECK(manager_);
 
   // Set up the desired (output) format specified by the client.
@@ -183,6 +189,7 @@ AUAudioInputStream::AUAudioInputStream(AudioManagerMac* manager,
 AUAudioInputStream::~AUAudioInputStream() {
   DVLOG(1) << "~dtor";
   DCHECK(!device_listener_is_active_);
+  ReportAndResetStats();
 }
 
 // Obtain and open the AUHAL AudioOutputUnit for recording.
@@ -463,6 +470,7 @@ void AUAudioInputStream::Stop() {
   DCHECK_EQ(result, noErr);
 
   SetInputCallbackIsActive(false);
+  ReportAndResetStats();
   sink_ = nullptr;
   fifo_.Clear();
   io_buffer_frame_size_ = 0;
@@ -760,6 +768,15 @@ OSStatus AUAudioInputStream::OnDataIsAvailable(
 OSStatus AUAudioInputStream::Provide(UInt32 number_of_frames,
                                      AudioBufferList* io_data,
                                      const AudioTimeStamp* time_stamp) {
+  UpdateCaptureTimestamp(time_stamp);
+  last_number_of_frames_ = number_of_frames;
+
+  // TODO(grunell): We'll only care about the first buffer size change, any
+  // further changes will be ignored. This is in line with output side stats.
+  // It would be nice to have all changes reflected in UMA stats.
+  if (number_of_frames != number_of_frames_ && number_of_frames_requested_ == 0)
+    number_of_frames_requested_ = number_of_frames;
+
   // Update the capture latency.
   double capture_latency_frames = GetCaptureLatency(time_stamp);
 
@@ -1147,4 +1164,61 @@ void AUAudioInputStream::AddDevicePropertyChangesToUMA(bool startup_failed) {
   device_property_changes_map_.clear();
 }
 
+void AUAudioInputStream::UpdateCaptureTimestamp(
+    const AudioTimeStamp* timestamp) {
+  if ((timestamp->mFlags & kAudioTimeStampSampleTimeValid) == 0)
+    return;
+
+  if (last_sample_time_) {
+    DCHECK_NE(0U, last_number_of_frames_);
+    UInt32 diff =
+        static_cast<UInt32>(timestamp->mSampleTime - last_sample_time_);
+    if (diff != last_number_of_frames_) {
+      DCHECK_GT(diff, last_number_of_frames_);
+      // We were given samples post what we expected. Update the glitch count
+      // etc. and keep a record of the largest glitch.
+      auto lost_frames = diff - last_number_of_frames_;
+      total_lost_frames_ += lost_frames;
+      if (lost_frames > largest_glitch_frames_)
+        largest_glitch_frames_ = lost_frames;
+      ++glitches_detected_;
+    }
+  }
+
+  // Store the last sample time for use next time we get called back.
+  last_sample_time_ = timestamp->mSampleTime;
+}
+
+void AUAudioInputStream::ReportAndResetStats() {
+  if (last_sample_time_ == 0)
+    return;  // No stats gathered to report.
+
+  // A value of 0 indicates that we got the buffer size we asked for.
+  UMA_HISTOGRAM_COUNTS("Media.Audio.Capture.FramesRequested",
+                       number_of_frames_requested_);

[Mark P, 2016/02/26 17:10:55]

Is the standard COUNTS histogram the right range?  Up to a million frames
requested.  That sounds implausible to me.  Maybe one of the other COUNTS
histograms has a better size.

[tommi (sloooow) - chröme, 2016/02/26 17:27:43]

These are audio "frames".  There will be tens of thousands of these per second,
so million is actually reasonable (it's about 20 seconds if we get 48000 frames
per second).

[Mark P, 2016/02/26 18:37:19]

Ah, thanks for the explanation.  This seems alright then.

[Henrik Grunell, 2016/02/29 17:48:48]

Actually, this is number of frames requested per callback, i.e. typically below
1000. Changed to COUNTS_10000.

+  // Even if there aren't any glitches, we want to record it to get a feel for
+  // how often we get no glitches vs the alternative.
+  UMA_HISTOGRAM_CUSTOM_COUNTS("Media.Audio.Capture.Glitches",
+                              glitches_detected_, 0, 999999, 100);

[Mark P, 2016/02/26 17:10:55]

With these parameters, the histogram looks basically identical to the standard
UMA_HISTOGRAM_COUNTS histogram.  Sure, the maximum bucket is 999,999 instead of
1,000,000 but I know you can't care about that.  Please use the standard counts
histogram unless you have a reason not to.

[tommi (sloooow) - chröme, 2016/02/26 17:27:43]

This doubles the bucket count though - or am I missing something?

[Mark P, 2016/02/26 18:37:19]

Ah, I see, you're using twice as many buckets as the default macro.  Do you have
a reason you need more than the typical amount of precision?

[Henrik Grunell, 2016/02/29 17:48:48]

Tommi, do you have the rationale for this? (Since this is based on the output
side stats you wrote.) I'd say 50 should be enough. Changed it to 50 meanwhile.

+
+  if (glitches_detected_ != 0) {
+    auto lost_frames_ms = (total_lost_frames_ * 1000) / format_.mSampleRate;
+    UMA_HISTOGRAM_COUNTS("Media.Audio.Capture.LostFramesInMs", lost_frames_ms);

[Mark P, 2016/02/26 17:10:55]

Either use one of the standard UMA times histograms or explain in a comment here
why you're instead using a COUNTS histogram.

[Henrik Grunell, 2016/02/29 17:48:48]

Changed to LONG_TIMES and below to CUSTOM_TIMES with 1 minute as max.

+    auto largest_glitch_ms =
+        (largest_glitch_frames_ * 1000) / format_.mSampleRate;
+    UMA_HISTOGRAM_COUNTS("Media.Audio.Capture.LargestGlitchMs",
+                         largest_glitch_ms);
+    DLOG(WARNING) << "Total glitches=" << glitches_detected_
+                  << ". Total frames lost=" << total_lost_frames_ << " ("
+                  << lost_frames_ms;
+  }
+
+  number_of_frames_requested_ = 0;
+  glitches_detected_ = 0;
+  last_sample_time_ = 0;
+  last_number_of_frames_ = 0;
+  total_lost_frames_ = 0;
+  largest_glitch_frames_ = 0;
+}
+
 }  // namespace media