Added automatic mode to FakeInputAudioStream to generate automatic beeps

media/audio/fake_audio_input_stream.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/audio/fake_audio_input_stream.h"
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
 #include "media/audio/audio_manager_base.h"
 
 using base::TimeTicks;
 using base::TimeDelta;
 
 namespace media {
 
 namespace {
 
 // These values are based on experiments for local-to-local
 // PeerConnection to demonstrate audio/video synchronization.
 const int kBeepDurationMilliseconds = 20;
 const int kBeepFrequency = 400;
 
+// Intervals between two automatic beeps.
+const int kAutomaticBeepIntervalInMs = 500;
+
+// Automatic beep will be triggered every |kAutomaticBeepIntervalInMs| unless
+// users explicitly call BeepOnce(), which will disable the automatic beep.
 struct BeepContext {
-  BeepContext() : beep_once(false) {}
+  BeepContext() : beep_once(false), automatic(true) {}
   base::Lock beep_lock;
   bool beep_once;
+  bool automatic;
 };
 
 static base::LazyInstance<BeepContext> g_beep_context =
     LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 AudioInputStream* FakeAudioInputStream::MakeFakeStream(
     AudioManagerBase* manager,
     const AudioParameters& params) {
@@ skipping 34 matching lines @@
   thread_.Start();
   thread_.message_loop()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&FakeAudioInputStream::DoCallback, base::Unretained(this)),
       callback_interval_);
 }
 
 void FakeAudioInputStream::DoCallback() {
   DCHECK(callback_);
 
+  const TimeTicks now = TimeTicks::Now();
+  base::TimeDelta next_callback_time =
+      last_callback_time_ + callback_interval_ * 2 - now;

[DaleCurtis, 2014/05/06 17:36:52]

Where does this *2 come from?

[no longer working on chromium, 2014/05/07 08:55:41]

This is old code moved from line 121.

I guess the formula is:
now - last_callback_time_ - callback_interval_ = delta_now
next_callback_time - callback_interval_ + delta_now = 0
That becomes:
next_callback_time - 2 * callback_interval_ +now - last_callback_time_ = 0

+
+  // If we are falling behind, try to catch up as much as we can in the next
+  // callback.
+  if (next_callback_time < base::TimeDelta())
+    next_callback_time = base::TimeDelta();
+
+  // Accumulate the time from the last beep.
+  interval_from_last_beep_ += now - last_callback_time_;
+
+  last_callback_time_ = now;
+
   memset(buffer_.get(), 0, buffer_size_);
 
   bool should_beep = false;
   {
     BeepContext* beep_context = g_beep_context.Pointer();
     base::AutoLock auto_lock(beep_context->beep_lock);
-    should_beep = beep_context->beep_once;
-    beep_context->beep_once = false;
+    if (beep_context->automatic) {
+      base::TimeDelta delta = interval_from_last_beep_ -
+          TimeDelta::FromMilliseconds(kAutomaticBeepIntervalInMs);
+      if (delta > base::TimeDelta()) {
+        should_beep = true;
+        interval_from_last_beep_ = delta;
+      }
+    } else {
+      should_beep = beep_context->beep_once;
+      beep_context->beep_once = false;
+    }
   }
 
   // If this object was instructed to generate a beep or has started to
   // generate a beep sound.
   if (should_beep || beep_generated_in_buffers_) {
     // Compute the number of frames to output high value. Then compute the
     // number of bytes based on channels and bits per channel.
     int high_frames = beep_period_in_frames_ / 2;
     int high_bytes = high_frames * params_.bits_per_sample() *
         params_.channels() / 8;
 
     // Separate high and low with the same number of bytes to generate a
     // square wave.
     int position = 0;
     while (position + high_bytes <= buffer_size_) {
       // Write high values first.
       memset(buffer_.get() + position, 128, high_bytes);
-
       // Then leave low values in the buffer with |high_bytes|.
       position += high_bytes * 2;
     }
 
     ++beep_generated_in_buffers_;
     if (beep_generated_in_buffers_ >= beep_duration_in_buffers_)
       beep_generated_in_buffers_ = 0;
   }
 
   callback_->OnData(this, buffer_.get(), buffer_size_, buffer_size_, 1.0);
   frames_elapsed_ += params_.frames_per_buffer();
 
-  const TimeTicks now = TimeTicks::Now();
-  base::TimeDelta next_callback_time =
-      last_callback_time_ + callback_interval_ * 2 - now;
-
-  // If we are falling behind, try to catch up as much as we can in the next
-  // callback.
-  if (next_callback_time < base::TimeDelta())
-    next_callback_time = base::TimeDelta();
-
-  last_callback_time_ = now;
   thread_.message_loop()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&FakeAudioInputStream::DoCallback, base::Unretained(this)),
       next_callback_time);
 }
 
 void FakeAudioInputStream::Stop() {
   thread_.Stop();
   callback_ = NULL;
 }
@@ skipping 17 matching lines @@
 
 bool FakeAudioInputStream::GetAutomaticGainControl() {
   return true;
 }
 
 // static
 void FakeAudioInputStream::BeepOnce() {
   BeepContext* beep_context = g_beep_context.Pointer();
   base::AutoLock auto_lock(beep_context->beep_lock);
   beep_context->beep_once = true;
+  beep_context->automatic = false;
 }
 
 }  // namespace media