Refactor MediaResource to be multi-stream capable

media/base/media_resource.h

 // Copyright 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.
 
 #ifndef MEDIA_BASE_MEDIA_RESOURCE_H_
 #define MEDIA_BASE_MEDIA_RESOURCE_H_
 
+#include <vector>
+
+#include "base/callback.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "media/base/demuxer_stream.h"
 #include "media/base/media_export.h"
 #include "media/base/media_url_params.h"
 #include "url/gurl.h"
 
 namespace media {
 
+// The callback that is used to notify clients about streams being enabled and
+// disabled. The first parameter is the DemuxerStream whose status changed. The
+// second parameter is a bool indicating whether the stream got enabled or
+// disabled. The third parameter specifies the media playback position at the
+// time the status change happened.
+using StreamStatusChangeCB =
+    base::RepeatingCallback<void(DemuxerStream*, bool, base::TimeDelta)>;
+
 // Abstract class that defines how to retrieve "media resources" in
 // DemuxerStream form (for most cases) or URL form (for the MediaPlayerRenderer
 // case).
 //
 // The derived classes must return a non-null value for the getter method
 // associated with their type, and return a null/empty value for other getters.
 class MEDIA_EXPORT MediaResource {
  public:
   enum Type {
     STREAM,  // Indicates GetStreams() should be used
     URL,     // Indicates GetUrl() should be used
   };
 
   MediaResource();
   virtual ~MediaResource();
 
   // For Type::STREAM:
-  //   Returns the first stream of the given stream type (which is not allowed
-  //   to be DemuxerStream::TEXT), or NULL if that type of stream is not
-  //   present.
+  // Returns a collection of available DemuxerStream objects. Note that some of
+  // those streams might be in disabled state (check DemuxerStream::enabled() ).
   //   NOTE: Once a DemuxerStream pointer is returned from GetStream it is
   //   guaranteed to stay valid for as long as the Demuxer/MediaResource
   //   is alive. But make no assumption that once GetStream returned a non-null
   //   pointer for some stream type then all subsequent calls will also return
   //   non-null pointer for the same stream type. In MSE Javascript code can
   //   remove SourceBuffer from a MediaSource at any point and this will make
   //   some previously existing streams inaccessible/unavailable.
-  // Other types:
-  //   Should not be called.
-  virtual DemuxerStream* GetStream(DemuxerStream::Type type) = 0;
+  virtual std::vector<DemuxerStream*> GetStreams() = 0;
 
   // For Type::URL:
   //   Returns the URL parameters of the media to play. Empty URLs are legal,
   //   and should be handled appropriately by the caller.
   // Other types:
   //   Should not be called.
   virtual MediaUrlParams GetMediaUrlParams() const;
 
   virtual MediaResource::Type GetType() const;
 
+  // The StreamStatusChangeCB allows clients to receive notifications about one
+  // of the streams being disabled or enabled.
+  virtual void SetStreamStatusChangeCB(const StreamStatusChangeCB& cb) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MediaResource);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MEDIA_RESOURCE_H_