Motown: Change player state machine to support preroll

services/media/factory_service/media_player_impl.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 MOJO_SERVICES_MEDIA_FACTORY_MEDIA_PLAYER_IMPL_H_
 #define MOJO_SERVICES_MEDIA_FACTORY_MEDIA_PLAYER_IMPL_H_
 
 #include <limits>
 #include <vector>
 
@@ skipping 33 matching lines @@
   void Pause() override;
 
   void Seek(int64_t position) override;
 
  private:
   static constexpr int64_t kMinimumLeadTime = Timeline::ns_from_ms(30);
 
   // Internal state.
   enum class State {
     kWaiting,  // Waiting for some work to complete.
-    kPaused,
-    kPlaying,
+    kFlushed,  // Paused with no data in the pipeline.
+    kPrimed,   // Paused with data in the pipeline.
+    kPlaying,  // Time is progressing.
   };
 
   struct Stream {
     Stream();
     ~Stream();
     // TODO(dalesat): Have the sink enlist the decoder.
     MediaTypeConverterPtr decoder_;
     MediaSinkPtr sink_;
     // The following fields are just temporaries used to solve lambda capture
     // problems.
     MediaProducerPtr encoded_producer_;
     MediaProducerPtr decoded_producer_;
     InterfaceHandle<MediaRenderer> renderer_;
   };
 
   MediaPlayerImpl(InterfaceHandle<SeekingReader> reader,
                   InterfaceHandle<MediaRenderer> audio_renderer,
                   InterfaceHandle<MediaRenderer> video_renderer,
                   InterfaceRequest<MediaPlayer> request,
                   MediaFactoryService* owner);
 
   // Takes action based on current state.
   void Update();
 
-  // Handles seeking in paused state.
-  void WhenPausedAndSeeking();
-
-  // Handles seeking in paused state with flushed pipeline.
-  void WhenFlushedAndSeeking();
-
-  // Sets the timeline transform. transform_subject_time_ is used for the
-  // subject_time, and the effective_reference_time is now plus
-  // kMinimumLeadTime.
-  void SetTimelineTransform(uint32_t reference_delta, uint32_t subject_delta);
-
   // Prepares a stream.
   void PrepareStream(Stream* stream,
                      size_t index,
                      const MediaTypePtr& input_media_type,
                      const std::function<void()>& callback);
 
   // Creates a sink for a stream.
   void CreateSink(Stream* stream,
                   const MediaTypePtr& input_media_type,
                   const std::function<void()>& callback);
 
   // Handles a metadata update from the demux. When called with the default
   // argument values, initiates demux metadata updates.
   void HandleDemuxMetadataUpdates(
       uint64_t version = MediaDemux::kInitialMetadata,
       MediaMetadataPtr metadata = nullptr);
 
   // Handles a status update from the control site. When called with the default
   // argument values, initiates control site. status updates.
   void HandleTimelineControlSiteStatusUpdates(
       uint64_t version = MediaTimelineControlSite::kInitialStatus,
       MediaTimelineControlSiteStatusPtr status = nullptr);
 
   MediaFactoryPtr factory_;
   MediaDemuxPtr demux_;
   MediaTimelineControllerPtr timeline_controller_;
   MediaTimelineControlSitePtr timeline_control_site_;
   TimelineConsumerPtr timeline_consumer_;
   std::vector<std::unique_ptr<Stream>> streams_;
+
+  // The state we're currently in.
   State state_ = State::kWaiting;
-  State target_state_ = State::kPaused;
-  bool flushed_ = true;
+
+  // The state we trying to transition to, either because the client has called
+  // |Play| or |Pause| or because we've hit end-of-stream.
+  State target_state_ = State::kFlushed;
+
+  // Whether we're currently at end-of-stream.
   bool end_of_stream_ = false;
+
+  // The position we want to seek to (because the client called Seek) or
+  // kUnspecifiedTime, which indicates there's no desire to seek.
   int64_t target_position_ = kUnspecifiedTime;
+
+  // The subject time to be used for SetTimelineTransform. The value is
+  // kUnspecifiedTime if there's no need to seek or the position we want to
+  // seek to if there is.
   int64_t transform_subject_time_ = kUnspecifiedTime;
+
+  // A function that translates local time into presentation time in ns.
   TimelineFunction timeline_function_;
+
   CallbackJoiner set_transform_joiner_;
   MediaMetadataPtr metadata_;
   MojoPublisher<GetStatusCallback> status_publisher_;
+
   // The following fields are just temporaries used to solve lambda capture
   // problems.
   InterfaceHandle<MediaRenderer> audio_renderer_;
   InterfaceHandle<MediaRenderer> video_renderer_;
 };
 
 }  // namespace media
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_MEDIA_FACTORY_MEDIA_PLAYER_IMPL_H_