Render inband text tracks in the media pipeline

media/filters/text_renderer_impl.h

+// Copyright (c) 2013 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 MEDIA_FILTERS_TEXT_RENDERER_IMPL_H_
+#define MEDIA_FILTERS_TEXT_RENDERER_IMPL_H_
+
+#include <vector>
+
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "media/base/media_export.h"
+#include "media/base/text_renderer.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace media {
+
+class TextBuffer;
+class TextDecoder;
+
+// Indicates that a cue has been delivered from the stream at |index|,
+// and hence that it should be added to the cue list for its text track.
+typedef base::Callback<void(int index,
+                            const scoped_refptr<TextBuffer>&)> CueReadyCB;
+
+// Receives the decoded cues from the upstream decoder and passes them
+// up to the player (via CueReadyCB) as they arrive.
+class MEDIA_EXPORT TextRendererImpl : public TextRenderer {
+ public:
+  // |message_loop| is the thread on which TextRendererImpl will execute.
+  //
+  // |decoder| contains the TextDecoder to use when initializing.
+  //
+  // |cue_ready_cb] is called when the read of a decoded cue completes.
+  TextRendererImpl(const scoped_refptr<base::MessageLoopProxy>& message_loop,
+                   scoped_ptr<TextDecoder> decoder,
+                   const CueReadyCB& cue_ready_cb);
+  virtual ~TextRendererImpl();
+
+  // TextRenderer implementation.
+  virtual void Initialize(Demuxer* demuxer,

[acolwell GONE FROM CHROMIUM, 2013/09/12 00:15:15]

I think there should be an AddStream(DemuxerStream) /
RemoveStream(DemuxerStream) pair on this class that allows tracks to be
added/removed during playback so we can properly handle the MSE case. 

This would remove the need for passing the demuxer to the Initialize() method.

[Matthew Heaney (Chromium), 2013/09/13 19:51:54]

OK.  I had written you a few questions about the exact mechanism you had in
mind, to confirm my understanding.

I'm thinking that we'll have to make some other adjustments to the TextDecoder
in order to handle this.

[Matthew Heaney (Chromium), 2013/09/20 23:53:54]

I added the new method(s) to DemuxerHost and Pipeline.

+                          const PipelineStatusCB& init_cb,
+                          const base::Closure& ended_cb) OVERRIDE;
+  virtual void Play(const base::Closure& callback) OVERRIDE;
+  virtual void Pause(const base::Closure& callback) OVERRIDE;
+  virtual void Stop(const base::Closure& callback) OVERRIDE;
+

[acolwell GONE FROM CHROMIUM, 2013/09/12 00:15:15]

I think there should be an AddTrack() / RemoveTrack() pair on this class that
allows tracks to be added/removed during playback so we can properly handle the
MSE case.

[Matthew Heaney (Chromium), 2013/09/13 19:51:54]

OK, I'll look into that.

+ private:
+  // Callback delivered by the text decoder, when the read on the text
+  // demuxer stream at |index| has completed, and the frame decoded.
+  void CueReady(int index, const scoped_refptr<TextBuffer>& text_buffer);
+
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
+  base::WeakPtrFactory<TextRendererImpl> weak_factory_;
+  base::WeakPtr<TextRendererImpl> weak_this_;
+  scoped_ptr<TextDecoder> decoder_;
+  const CueReadyCB cue_ready_cb_;
+
+  // Callbacks provided during Initialize().
+  PipelineStatusCB init_cb_;
+  base::Closure ended_cb_;
+
+  // Callback provided to Pause().
+  base::Closure pause_cb_;
+
+  // Callback provided to Stop().
+  base::Closure stop_cb_;
+
+  // After Initialize() has completed, all variables below must be accessed
+  // under |lock_|. ------------------------------------------------------------
+  base::Lock lock_;

[acolwell GONE FROM CHROMIUM, 2013/09/12 00:15:15]

Do you really need this lock? Doesn't this code only run on the media thread?

[Matthew Heaney (Chromium), 2013/09/13 19:51:54]

Done.

+
+  // Simple state tracking variable.
+  enum State {
+    kUninitialized,
+    kPausePending,
+    kPaused,
+    kPlaying,
+    kStopPending,
+    kStopped
+  };
+  State state_;
+
+  // To differentiate among demuxer stream kinds, and determine read progress.
+  enum ReadState {
+    kReadInactive,
+    kReadIdle,
+    kReadPending
+  };
+  std::vector<ReadState> read_state_;
+
+  // Indicates how many text streams, among all demuxer streams.
+  int text_stream_count_;
+
+  // Indicates how many read requests are in flight.
+  int pending_read_count_;
+
+  // Indicates how many text streams have delivered end-of-stream indications.

[acolwell GONE FROM CHROMIUM, 2013/09/12 00:15:15]

nit: This comment does not appear to match the code. IIUC it actually holds the
number of streams that haven't ended yet.

[Matthew Heaney (Chromium), 2013/09/13 19:51:54]

Done.

+  int eos_count_;
+
+  // End variables which must be accessed under |lock_|. ----------------------
+
+  DISALLOW_COPY_AND_ASSIGN(TextRendererImpl);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_TEXT_RENDERER_IMPL_H_