MediaCaptureFromElement: add support for audio captureStream().

content/renderer/media/html_audio_element_capturer_source.h

+// 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.
+
+#ifndef CONTENT_RENDERER_MEDIA_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_
+#define CONTENT_RENDERER_MEDIA_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_
+
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
+#include "base/threading/thread_checker.h"
+#include "content/common/content_export.h"
+#include "media/base/audio_capturer_source.h"
+#include "media/base/audio_converter.h"
+#include "media/blink/webaudiosourceprovider_impl.h"
+
+#if !defined(ENABLE_WEBRTC)
+#error "Testing testing"
+#endif
+
+namespace blink {
+class WebMediaPlayer;
+}  // namespace blink
+
+namespace media {
+class AudioBus;
+class AudioFifo;
+}  // namespace media
+
+namespace content {
+
+// This class is an AudioCapturerSource registering to the constructor-passed
+// weak WebAudioSourceProviderImpl to receive a copy of the audio data intended
+// for rendering. This copied data is received on OnAudioBus(), converted and
+// sent to |capture_callback_|
+class CONTENT_EXPORT HtmlAudioElementCapturerSource final
+    : NON_EXPORTED_BASE(public media::AudioCapturerSource),
+      NON_EXPORTED_BASE(public media::AudioConverter::InputCallback) {
+ public:
+  static scoped_refptr<HtmlAudioElementCapturerSource>
+  CreateFromWebMediaPlayerImpl(blink::WebMediaPlayer* player);
+
+  explicit HtmlAudioElementCapturerSource(
+      const base::WeakPtr<media::WebAudioSourceProviderImpl>& audio_source);
+
+  // media::AudioCapturerSource Implementation.
+  void Initialize(const media::AudioParameters& params,
+                  CaptureCallback* callback,
+                  int session_id) override;
+  void Start() override;
+  void Stop() override;
+  void SetVolume(double volume) override;
+  void SetAutomaticGainControl(bool enable) override;
+
+  // To act as an WebAudioSourceProviderImpl::CopyAudioCB.
+  void OnAudioBus(std::unique_ptr<media::AudioBus> audio_bus,

[miu, 2016/05/13 23:40:35]

Seems like this should be a private method since it should only be called via
the internally-created callback.

[mcasas, 2016/05/14 02:23:47]

Done.

+                  uint32_t delay_milliseconds,
+                  int sample_rate);
+
+  // media::AudioConverted::InputCallback implementation.
+  double ProvideInput(media::AudioBus* audio_bus,

[miu, 2016/05/13 23:40:35]

Looks like this is for exclusive use by |converter_|, so consider making it a
private method too.

[mcasas, 2016/05/14 02:23:47]

Done.

+                      base::TimeDelta buffer_delay) override;
+
+ private:
+  ~HtmlAudioElementCapturerSource() override;
+  void CreateConverter();
+
+  const media::WebAudioSourceProviderImpl::CopyAudioCB audio_input_cb_;
+
+  base::WeakPtr<media::WebAudioSourceProviderImpl> audio_source_;
+
+  media::AudioParameters input_params_;  // Format we see ingressing.
+  media::AudioParameters output_params_;  // Format we need to egress.
+
+  // Sampling rate adapter between |input_params_| and |output_params_|.
+  std::unique_ptr<media::AudioConverter> converter_;
+  std::unique_ptr<media::AudioFifo> fifo_;
+  int min_fifo_frames_for_conversion_;
+
+  CaptureCallback* capture_callback_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(HtmlAudioElementCapturerSource);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_HTML_AUDIO_ELEMENT_CAPTURER_SOURCE_H_