[PPAPI] Pepper MediaStream API audio track implementation and example.

content/renderer/pepper/pepper_media_stream_audio_track_host.cc

+// Copyright (c) 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 "content/renderer/pepper/pepper_media_stream_audio_track_host.h"
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/message_loop/message_loop_proxy.h"
+#include "ppapi/c/pp_errors.h"
+#include "ppapi/c/ppb_audio_frame.h"
+#include "ppapi/shared_impl/media_stream_frame.h"
+
+namespace {
+
+// TODO(penghuang): make it configurable.
+const int32_t kNumberOfFrames = 4;
+
+}  // namespace
+
+namespace content {
+
+PepperMediaStreamAudioTrackHost::PepperMediaStreamAudioTrackHost(
+    RendererPpapiHost* host,
+    PP_Instance instance,
+    PP_Resource resource,
+    const blink::WebMediaStreamTrack& track)
+    : PepperMediaStreamTrackHostBase(host, instance, resource),
+      track_(track),
+      connected_(false),
+      frame_data_size_(0),
+      main_message_loop_proxy_(base::MessageLoopProxy::current()),
+      weak_factory_(this) {
+  DCHECK(!track_.isNull());
+}
+
+PepperMediaStreamAudioTrackHost::~PepperMediaStreamAudioTrackHost() {
+  OnClose();
+}
+
+void PepperMediaStreamAudioTrackHost::InitFramesOnMainThread(
+    uint32_t number_of_frames, uint32_t frame_size) {
+  bool result = InitFrames(number_of_frames, frame_size);
+  DCHECK(result);
+}
+
+void PepperMediaStreamAudioTrackHost::OnClose() {
+  if (connected_) {
+    MediaStreamAudioSink::RemoveFromAudioTrack(this, track_);
+    connected_ = false;
+  }
+}
+
+void PepperMediaStreamAudioTrackHost::OnData(const int16* audio_data,
+                                             int sample_rate,
+                                             int number_of_channels,
+                                             int number_of_frames) {
+  DCHECK(audio_data);
+  DCHECK_EQ(sample_rate, audio_params_.sample_rate());
+  DCHECK_EQ(number_of_channels, audio_params_.channels());
+  DCHECK_EQ(number_of_frames, audio_params_.frames_per_buffer());
+
+  int32_t index = frame_buffer()->DequeueFrame();
+  // Drop frames if the underlying buffer is full or not initialized.
+  if (index >= 0) {
+    // TODO(penghuang): support re-sampling, etc.
+    ppapi::MediaStreamFrame::Audio* frame =
+        &(frame_buffer()->GetFramePointer(index)->audio);
+    frame->header.size = frame_buffer()->frame_size();
+    frame->header.type = ppapi::MediaStreamFrame::TYPE_AUDIO;
+    frame->timestamp = timestamp_.InMillisecondsF();
+    frame->sample_rate = static_cast<PP_AudioSampleRate>(sample_rate);
+    frame->number_of_channels = number_of_channels;
+    frame->number_of_samples = number_of_channels * number_of_frames;
+    frame->data_size = frame_data_size_;
+
+    memcpy(frame->data, audio_data, frame_data_size_);
+    SendEnqueueFrameMessageToPlugin(index);
+  }
+  timestamp_ += frame_duration_;
+}
+
+void PepperMediaStreamAudioTrackHost::OnSetFormat(
+    const media::AudioParameters& params) {
+  DCHECK(!audio_params_.IsValid());
+  DCHECK(params.IsValid());
+  DCHECK_EQ(params.bits_per_sample(), 16);
+
+  // TODO(penghuang): support setting format more than once.
+  audio_params_ = params;
+  frame_duration_ = audio_params_.GetBufferDuration();
+  frame_data_size_ = audio_params_.GetBytesPerBuffer();
+  int32_t size = sizeof(ppapi::MediaStreamFrame::Audio) + frame_data_size_;

[dmichael (off chromium), 2014/01/16 22:34:20]

I don't know if we care, but this size calculation comes out bigger than you
need, because the data part of MediaStreamFrame::Audio has non-zero size. Maybe
just comment. Probably not worth the effort to shave bytes here.

(PS: Same is true for Video, I think)

[Peng, 2014/01/17 00:23:49]

Done.

+
+  main_message_loop_proxy_->PostTask(

[dmichael (off chromium), 2014/01/16 22:34:20]

What thread is this coming in on? Do you know the calling thread for all of
these functions? This looks a little unusual here, at least in the absence of
more documentation.

The Chromium approach is usually to have each class run on a designated thread.
So if you're dealing with two or more threads, it may make sense to split
functionality. At the very least, it needs to be obvious for each function what
thread(s) it runs on.

[Peng, 2014/01/17 00:23:49]

OnData() & OnSetFormat() are called from an Audio Thread. Because the
InitFrames() will do some sync IPC, so have to do it in main thread.:(

I add some document here. Not sure if it is enough. Done

+      FROM_HERE,
+      base::Bind(&PepperMediaStreamAudioTrackHost::InitFramesOnMainThread,
+                 weak_factory_.GetWeakPtr(), kNumberOfFrames, size));
+}
+
+void PepperMediaStreamAudioTrackHost::DidConnectPendingHostToResource() {
+  if (!connected_) {
+    MediaStreamAudioSink::AddToAudioTrack(this, track_);
+    connected_ = true;
+  }
+}
+
+}  // namespace content