MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/external_media_stream_audio_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/external_media_stream_audio_source.h"
+
+namespace content {
+
+ExternalMediaStreamAudioSource::ExternalMediaStreamAudioSource(
+    scoped_refptr<media::AudioCapturerSource> source,
+    int sample_rate,
+    media::ChannelLayout channel_layout,
+    int frames_per_buffer,
+    bool is_remote)
+    : MediaStreamAudioSource(!is_remote), source_(std::move(source)),
+      was_started_(false) {
+  DVLOG(1)
+      << "ExternalMediaStreamAudioSource::ExternalMediaStreamAudioSource()";
+  DCHECK(source_.get());
+  MediaStreamAudioSource::SetFormat(media::AudioParameters(
+      media::AudioParameters::AUDIO_PCM_LOW_LATENCY, channel_layout,
+      sample_rate,
+      16,  // Legacy parameter (data is always in 32-bit float format).
+      frames_per_buffer));
+}
+
+ExternalMediaStreamAudioSource::~ExternalMediaStreamAudioSource() {
+  DVLOG(1)
+      << "ExternalMediaStreamAudioSource::~ExternalMediaStreamAudioSource()";
+  EnsureSourceIsStopped();
+}
+
+bool ExternalMediaStreamAudioSource::EnsureSourceIsStarted() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (was_started_)
+    return true;
+  VLOG(1) << "Starting externally-provided "
+          << (is_local_source() ? "local" : "remote")
+          << " source with audio parameters={"
+          << GetAudioParameters().AsHumanReadableString() << "}.";
+  source_->Initialize(GetAudioParameters(), this, -1);
+  source_->Start();
+  was_started_ = true;
+  return true;
+}
+
+void ExternalMediaStreamAudioSource::EnsureSourceIsStopped() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!source_)
+    return;
+  if (was_started_)
+    source_->Stop();
+  source_ = nullptr;
+  VLOG(1) << "Stopped externally-provided "
+          << (is_local_source() ? "local" : "remote")
+          << " source with audio parameters={"
+          << GetAudioParameters().AsHumanReadableString() << "}.";
+}
+
+void ExternalMediaStreamAudioSource::Capture(const media::AudioBus* audio_bus,
+                                             int audio_delay_milliseconds,
+                                             double volume,
+                                             bool key_pressed) {
+  DCHECK(audio_bus);
+  // TODO(miu): Plumbing is needed to determine the actual capture timestamp
+  // of the audio, instead of just snapshotting TimeTicks::Now(), for proper
+  // audio/video sync. http://crbug.com/335335
+  MediaStreamAudioSource::DeliverDataToTracks(
+      *audio_bus,
+      base::TimeTicks::Now() -
+          base::TimeDelta::FromMilliseconds(audio_delay_milliseconds));
+}
+
+void ExternalMediaStreamAudioSource::OnCaptureError(const std::string& why) {
+  // As of this writing, this method doesn't get called for anything useful,
+  // and all other implementors just log the message, but don't disconnect sinks
+  // or take any other action. So, just log the error.
+  LOG(ERROR) << why;
+}
+
+}  // namespace content