MediaCaptureFromElement: add support for audio captureStream().

content/renderer/media/html_audio_element_capturer_source.cc

+// Copyright 2016 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 "content/renderer/media/html_audio_element_capturer_source.h"
+
+#include "base/threading/thread_task_runner_handle.h"
+#include "media/base/audio_parameters.h"
+#include "media/base/audio_renderer_sink.h"
+#include "media/blink/webaudiosourceprovider_impl.h"
+#include "media/blink/webmediaplayer_impl.h"
+#include "third_party/WebKit/public/platform/WebMediaPlayer.h"
+
+namespace content {
+
+//static
+HtmlAudioElementCapturerSource*
+HtmlAudioElementCapturerSource::CreateFromWebMediaPlayerImpl(
+    blink::WebMediaPlayer* player) {
+  DCHECK(player);
+  return new HtmlAudioElementCapturerSource(
+      static_cast<media::WebAudioSourceProviderImpl*>(
+          player->getAudioSourceProvider()));
+}
+
+HtmlAudioElementCapturerSource::HtmlAudioElementCapturerSource(
+    media::WebAudioSourceProviderImpl* audio_source)
+    : MediaStreamAudioSource(true /* is_local_source */),
+      audio_source_(audio_source),
+      is_started_(false),
+      last_sample_rate_(0),
+      last_num_channels_(0),
+      last_bus_frames_(0) {
+  DCHECK(audio_source_);
+}
+
+HtmlAudioElementCapturerSource::~HtmlAudioElementCapturerSource() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  EnsureSourceIsStopped();
+}
+
+bool HtmlAudioElementCapturerSource::EnsureSourceIsStarted() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (audio_source_ && !is_started_) {
+    // base:Unretained() is safe here since EnsureSourceIsStopped() guarantees
+    // no more calls to OnAudioBus().
+    audio_source_->SetCopyAudioCallback(base::Bind(
+        &HtmlAudioElementCapturerSource::OnAudioBus, base::Unretained(this)));
+    is_started_ = true;
+  }
+  return is_started_;
+}
+
+void HtmlAudioElementCapturerSource::EnsureSourceIsStopped() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!is_started_)
+    return;
+
+  if (audio_source_) {
+    audio_source_->ClearCopyAudioCallback();
+    audio_source_ = nullptr;
+  }
+  is_started_ = false;
+}
+
+void HtmlAudioElementCapturerSource::OnAudioBus(
+    std::unique_ptr<media::AudioBus> audio_bus,
+    uint32_t delay_milliseconds,
+    int sample_rate) {
+  const base::TimeTicks capture_time =
+      base::TimeTicks::Now() -
+      base::TimeDelta::FromMilliseconds(delay_milliseconds);
+
+  if (sample_rate != last_sample_rate_ ||
+      audio_bus->channels() != last_num_channels_ ||
+      audio_bus->frames() != last_bus_frames_) {
+    MediaStreamAudioSource::SetFormat(
+        media::AudioParameters(media::AudioParameters::AUDIO_PCM_LOW_LATENCY,
+                               media::GuessChannelLayout(audio_bus->channels()),
+                               sample_rate, 16, audio_bus->frames()));
+    last_sample_rate_ = sample_rate;
+    last_num_channels_ = audio_bus->channels();
+    last_bus_frames_ = audio_bus->frames();
+  }
+
+  MediaStreamAudioSource::DeliverDataToTracks(*audio_bus, capture_time);
+}
+
+}  // namespace content