Add a buffering controller for Chromecast.

chromecast/media/cma/base/buffering_controller.cc

+// Copyright 2014 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 "chromecast/media/cma/base/buffering_controller.h"
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/message_loop/message_loop_proxy.h"
+#include "chromecast/media/cma/base/buffering_state.h"
+#include "chromecast/media/cma/base/cma_logging.h"
+#include "media/base/buffers.h"
+
+namespace media {
+namespace cma {
+
+BufferingController::BufferingController(
+    const scoped_refptr<BufferingConfig>& config,
+    const BufferingNotificationCb& buffering_notification_cb)
+    : weak_factory_(this),

[lcwu1, 2014/08/28 02:14:58]

While it won't affect code correctness language-wise, I think in general people
initialize the class members in the same order as they are declared. (I don't
know whether there is a style guide about it though.)

[damienv1, 2014/08/29 15:09:05]

I changed the order in the header file and forgot to change the initialization
list.
Done.

+      config_(config),
+      buffering_notification_cb_(buffering_notification_cb),
+      is_buffering_(false),
+      begin_buffering_time_(base::Time()) {
+  weak_this_ = weak_factory_.GetWeakPtr();
+  thread_checker_.DetachFromThread();
+}
+
+BufferingController::~BufferingController() {
+  // Some weak pointers might possibly be invalidated here.
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+void BufferingController::UpdateHighLevelThreshold(
+    base::TimeDelta high_level_threshold) {
+  // Can only decrease the high level threshold.
+  if (high_level_threshold > config_->high_level())
+    return;
+  CMALOG(kLogControl) << "High buffer threshold: "
+                      << high_level_threshold.InMilliseconds();
+  config_->set_high_level(high_level_threshold);
+
+  // Make sure the low level threshold is somewhat consistent.
+  // Currently, we set it to one third of the high level threshold:
+  // this value could be adjusted in the future.
+  base::TimeDelta low_level_threshold = high_level_threshold / 3;
+  if (low_level_threshold <= config_->low_level()) {
+    CMALOG(kLogControl) << "Low buffer threshold: "
+                        << low_level_threshold.InMilliseconds();
+    config_->set_low_level(low_level_threshold);
+  }
+
+  // Signal all the streams the config has changed.
+  for (StreamList::iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    (*it)->OnConfigChanged();
+  }
+
+  // Once all the streams have been notified, the buffering state must be
+  // updated (no notification is received from the streams).
+  OnBufferingStateChanged(false, false);
+}
+
+scoped_refptr<BufferingState> BufferingController::AddStream() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // Add a new stream to the list of streams being monitored.
+  scoped_refptr<BufferingState> buffering_state(new BufferingState(
+      config_,
+      base::Bind(&BufferingController::OnBufferingStateChanged, weak_this_,
+                 false, false),
+      base::Bind(&BufferingController::UpdateHighLevelThreshold, weak_this_)));
+  stream_list_.push_back(buffering_state);
+
+  // Update the state and force a notification to the streams.
+  // TODO(damienv): Should this be a PostTask ?
+  OnBufferingStateChanged(true, false);
+
+  return buffering_state;
+}
+
+void BufferingController::SetMediaTime(base::TimeDelta time) {
+  for (StreamList::iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    (*it)->SetMediaTime(time);
+  }
+}
+
+base::TimeDelta BufferingController::GetMaxRenderingTime() const {
+  base::TimeDelta max_rendering_time(kNoTimestamp());
+  for (StreamList::const_iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    base::TimeDelta max_stream_rendering_time =
+        (*it)->GetMaxRenderingTime();
+    if (max_stream_rendering_time == kNoTimestamp())
+      return kNoTimestamp();
+    if (max_rendering_time == kNoTimestamp() ||
+        max_stream_rendering_time < max_rendering_time) {
+      max_rendering_time = max_stream_rendering_time;
+    }
+  }
+  return max_rendering_time;
+}
+
+void BufferingController::Reset() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  is_buffering_ = false;
+  stream_list_.clear();
+}
+
+void BufferingController::OnBufferingStateChanged(
+    bool force_notification, bool buffering_timeout) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // Log the state of each stream.
+  DumpState();
+
+  bool is_low_buffering = IsLowBufferLevel();
+  bool is_high_buffering = !is_low_buffering;
+  if (!buffering_timeout) {
+    // Hysteresis:
+    // - to leave buffering, not only should we leave the low buffer level state
+    //   but we should go to the high buffer level state (medium is not enough).
+    is_high_buffering = IsHighBufferLevel();
+  }
+
+  bool is_buffering_prv = is_buffering_;
+  if (is_buffering_) {
+    if (is_high_buffering)
+      is_buffering_ = false;
+  } else {
+    if (is_low_buffering)
+      is_buffering_ = true;
+  }
+
+  // Start buffering.
+  if (is_buffering_ && !is_buffering_prv) {
+    begin_buffering_time_ = base::Time::Now();
+  }
+
+  // End buffering.
+  if (is_buffering_prv && !is_buffering_) {
+    // TODO(damienv): |buffering_user_time| could be a UMA histogram.
+    base::Time current_time = base::Time::Now();
+    base::TimeDelta buffering_user_time = current_time - begin_buffering_time_;
+    CMALOG(kLogControl)
+        << "Buffering took: "
+        << buffering_user_time.InMilliseconds() << "ms";
+  }
+
+  if (is_buffering_prv != is_buffering_ || force_notification)
+    buffering_notification_cb_.Run(is_buffering_);
+}
+
+bool BufferingController::IsHighBufferLevel() {
+  if (stream_list_.empty())
+    return true;
+
+  bool is_high_buffering = true;
+  for (StreamList::iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    BufferingState::State stream_state = (*it)->GetState();
+    is_high_buffering = is_high_buffering &&
+        ((stream_state == BufferingState::kHighLevel) ||
+         (stream_state == BufferingState::kEosReached));
+  }
+  return is_high_buffering;
+}
+
+bool BufferingController::IsLowBufferLevel() {
+  if (stream_list_.empty())
+    return false;
+
+  for (StreamList::iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    BufferingState::State stream_state = (*it)->GetState();
+    if (stream_state == BufferingState::kLowLevel)
+      return true;
+  }
+
+  return false;
+}
+
+void BufferingController::DumpState() const {
+  CMALOG(kLogControl) << __FUNCTION__;
+  for (StreamList::const_iterator it = stream_list_.begin();
+       it != stream_list_.end(); ++it) {
+    CMALOG(kLogControl) << (*it)->ToString();
+  }
+}
+
+}  // namespace cma
+}  // namespace media