Make rendering of MediaStreams reflect changes to its set of tracks.

content/renderer/media/webmediaplayer_ms.cc

Index: content/renderer/media/webmediaplayer_ms.cc
diff --git a/content/renderer/media/webmediaplayer_ms.cc b/content/renderer/media/webmediaplayer_ms.cc
index f064d1ca786917cbb92d6ac228108fb099550fce..92c65e34269605a01181fb705648649f0f4577ee 100644
--- a/content/renderer/media/webmediaplayer_ms.cc
+++ b/content/renderer/media/webmediaplayer_ms.cc
@@ -20,6 +20,8 @@
 #include "content/public/renderer/media_stream_audio_renderer.h"
 #include "content/public/renderer/media_stream_renderer_factory.h"
 #include "content/public/renderer/media_stream_video_renderer.h"
+#include "content/renderer/media/media_stream_audio_track.h"
+#include "content/renderer/media/media_stream_video_track.h"
 #include "content/renderer/media/web_media_element_source_utils.h"
 #include "content/renderer/media/webmediaplayer_ms_compositor.h"
 #include "content/renderer/render_frame_impl.h"
@@ -190,6 +192,12 @@ WebMediaPlayerMS::~WebMediaPlayerMS() {
   DVLOG(1) << __func__;
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (!web_stream_.IsNull()) {
+    MediaStream* native_stream = MediaStream::GetMediaStream(web_stream_);
+    if (native_stream)
+      native_stream->RemoveObserver(this);

[foolip, 2017/07/05 08:49:44]

Can a DCHECK be added here or in the management of web_stream_ that makes sure
that if we reach this line, we have also called AddObserver for the same object?

[Guido Urdaneta, 2017/07/05 13:05:02]

RemoveObserver DCHECKs that its observer argument has been previously added with
AddObserver. See
https://cs.chromium.org/chromium/src/content/renderer/media/media_stream.cc?t...
I guess that's enough. 

[foolip, 2017/07/05 13:13:52]

Yep.

+  }
+
   // Destruct compositor resources in the proper order.
   get_client()->SetWebLayer(nullptr);
   if (video_weblayer_)
@@ -223,24 +231,29 @@ void WebMediaPlayerMS::Load(LoadType load_type,
   // TODO(acolwell): Change this to DCHECK_EQ(load_type, LoadTypeMediaStream)
   // once Blink-side changes land.
   DCHECK_NE(load_type, kLoadTypeMediaSource);
-  blink::WebMediaStream web_stream =
-      GetWebMediaStreamFromWebMediaPlayerSource(source);
+  web_stream_ = GetWebMediaStreamFromWebMediaPlayerSource(source);
+  if (!web_stream_.IsNull()) {
+    MediaStream* native_stream = MediaStream::GetMediaStream(web_stream_);
+    if (native_stream)
+      native_stream->AddObserver(this);
+  }
 
   compositor_ = new WebMediaPlayerMSCompositor(
-      compositor_task_runner_, io_task_runner_, web_stream, AsWeakPtr());
+      compositor_task_runner_, io_task_runner_, web_stream_, AsWeakPtr());
 
   SetNetworkState(WebMediaPlayer::kNetworkStateLoading);
   SetReadyState(WebMediaPlayer::kReadyStateHaveNothing);
   std::string stream_id =
-      web_stream.IsNull() ? std::string() : web_stream.Id().Utf8();
+      web_stream_.IsNull() ? std::string() : web_stream_.Id().Utf8();
   media_log_->AddEvent(media_log_->CreateLoadEvent(stream_id));
 
   frame_deliverer_.reset(new WebMediaPlayerMS::FrameDeliverer(
       AsWeakPtr(),
       base::Bind(&WebMediaPlayerMSCompositor::EnqueueFrame, compositor_)));
   video_frame_provider_ = renderer_factory_->GetVideoRenderer(
-      web_stream, media::BindToCurrentLoop(base::Bind(
-                      &WebMediaPlayerMS::OnSourceError, AsWeakPtr())),
+      web_stream_,
+      media::BindToCurrentLoop(
+          base::Bind(&WebMediaPlayerMS::OnSourceError, AsWeakPtr())),
       frame_deliverer_->GetRepaintCallback(), io_task_runner_,
       media_task_runner_, worker_task_runner_, gpu_factories_);
 
@@ -253,7 +266,7 @@ void WebMediaPlayerMS::Load(LoadType load_type,
                          media_log_.get());
 
     audio_renderer_ = renderer_factory_->GetAudioRenderer(
-        web_stream, frame->GetRoutingID(), initial_audio_output_device_id_,
+        web_stream_, frame->GetRoutingID(), initial_audio_output_device_id_,
         initial_security_origin_);
   }
 
@@ -275,6 +288,59 @@ void WebMediaPlayerMS::Load(LoadType load_type,
   }
 }
 
+void WebMediaPlayerMS::TrackAdded(const blink::WebMediaStreamTrack& track) {
+  Reload();
+}

[foolip, 2017/07/05 08:49:44]

Blank lines between functions seems to be the norm in this file.

[Guido Urdaneta, 2017/07/05 13:05:02]

Done.

+void WebMediaPlayerMS::TrackRemoved(const blink::WebMediaStreamTrack& track) {
+  Reload();
+}
+void WebMediaPlayerMS::Reload() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  blink::WebVector<blink::WebMediaStreamTrack> video_tracks;
+  web_stream_.VideoTracks(video_tracks);
+  bool has_video_track = !video_tracks.IsEmpty() &&
+                         MediaStreamVideoTrack::GetTrack(video_tracks[0]);
+
+  if (has_video_track && !video_frame_provider_) {
+    // Video track was added.
+    video_frame_provider_ = renderer_factory_->GetVideoRenderer(
+        web_stream_,
+        media::BindToCurrentLoop(
+            base::Bind(&WebMediaPlayerMS::OnSourceError, AsWeakPtr())),
+        frame_deliverer_->GetRepaintCallback(), io_task_runner_,
+        media_task_runner_, worker_task_runner_, gpu_factories_);
+    DCHECK(video_frame_provider_);
+    video_frame_provider_->Start();
+  } else if (video_frame_provider_ && !has_video_track) {
+    // Video track was removed.
+    video_frame_provider_->Stop();
+    video_frame_provider_ = nullptr;
+  }
+
+  RenderFrame* const frame = RenderFrame::FromWebFrame(frame_);
+  if (frame) {
+    blink::WebVector<blink::WebMediaStreamTrack> audio_tracks;
+    web_stream_.AudioTracks(audio_tracks);

[foolip, 2017/07/05 08:49:44]

Can you add a comment explaining that this is a getter?

[Guido Urdaneta, 2017/07/05 13:05:02]

Done. Also for VideoTracks above.

+    bool has_audio_track = !audio_tracks.IsEmpty() &&
+                           MediaStreamAudioTrack::GetTrack(audio_tracks[0]);
+
+    if (has_audio_track && !audio_renderer_) {
+      // Audio track was added.
+      audio_renderer_ = renderer_factory_->GetAudioRenderer(
+          web_stream_, frame->GetRoutingID(), initial_audio_output_device_id_,
+          initial_security_origin_);
+      audio_renderer_->SetVolume(volume_);
+      audio_renderer_->Start();
+      audio_renderer_->Play();
+    } else if (!has_audio_track && audio_renderer_) {
+      // Audio track was removed.
+      audio_renderer_->Stop();
+      audio_renderer_ = nullptr;
+    }
+  }
+}
+
 void WebMediaPlayerMS::Play() {
   DVLOG(1) << __func__;
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -381,6 +447,9 @@ bool WebMediaPlayerMS::HasAudio() const {
 
 blink::WebSize WebMediaPlayerMS::NaturalSize() const {
   DCHECK(thread_checker_.CalledOnValidThread());
+  if (!video_frame_provider_)
+    return blink::WebSize();
+
   if (video_rotation_ == media::VIDEO_ROTATION_90 ||
       video_rotation_ == media::VideoRotation::VIDEO_ROTATION_270) {
     const gfx::Size& current_size = compositor_->GetCurrentSize();