Media Source dispatches inband text tracks

media/base/pipeline_status.h

 // Copyright (c) 2012 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_BASE_PIPELINE_STATUS_H_
 #define MEDIA_BASE_PIPELINE_STATUS_H_
 
 #include "base/callback.h"
 
 #include <string>
@@ skipping 42 matching lines @@
 
   uint32 audio_bytes_decoded;  // Should be uint64?
   uint32 video_bytes_decoded;  // Should be uint64?
   uint32 video_frames_decoded;
   uint32 video_frames_dropped;
 };
 
 // Used for updating pipeline statistics.
 typedef base::Callback<void(const PipelineStatistics&)> StatisticsCB;
 
+// Specifies the varieties of text tracks.
+enum TextKind {

[acolwell GONE FROM CHROMIUM, 2013/04/05 16:29:23]

nit: This doesn't seem like the right home for this especially since the
pipeline isn't even involved in any of these changes. I think this should be put
in something like media/base/text_track.h

[Matthew Heaney (Chromium), 2013/05/08 19:53:00]

Done.

+  kTextSubtitles,
+  kTextCaptions,
+  kTextDescriptions,
+  kTextMetadata,
+  kTextNone
+};
+
+// So pipeline can notify media player about presence of text tracks.
+// TODO(matthewjheaney): Might have to also include track number, etc.
+typedef base::Callback<void(TextKind kind,
+                            const std::string& label,
+                            const std::string& language)> TextTrackCB;

[acolwell GONE FROM CHROMIUM, 2013/04/05 16:29:23]

nit:s/TextTrackCB/AddTextTrackCB

It seems like this method should return a callback or object for adding cues and
allowing the track to be removed. If you do this, I think you can avoid having
to pass IDs through this interface.

[Matthew Heaney (Chromium), 2013/05/08 19:53:00]

Can you elaborate a bit on this?  We're still a little fuzzy here in MTV about
how all the callback stuff works.

Are you saying that the TextTrackCB should change its return type from void to
some other callback type?  (A callback that returns a callback?)  Or that a new
interface should be added?  Or only that chunk_demuxer (or similar) should have
a new method?

[acolwell GONE FROM CHROMIUM, 2013/05/08 20:51:29]

Sure. At this point I think the return type should be something along the lines
of scoped_ptr<TextTrack> where TextTrack is declared along these lines:

class TextTrack {
  virtual ~TextTrack() {}
  virtual void addCue(const base::TimeDelta& start, const base::TimeDelta& end,
const std::string& id, const std::string& content, const std::string& settings)
= 0;
}

This basically mirrors the WebInbandTextTrackClient interface you added. When
this object gets destroyed it should remove the track from the presentation.

The abstract TextTrack declaration should be declared in
media/base/text_track.h, but the concrete implementation of this interface
should be in webkit/media/ since it will likely hold a reference to a
WebKit::WebInbandTextTrackClient and you can't reference Blink interfaces from
media/ code.

+
 }  // namespace media
 
 #endif  // MEDIA_BASE_PIPELINE_STATUS_H_