Generate and assign media track ids in demuxers.

media/base/media_track.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 MEDIA_BASE_MEDIA_TRACK_H_
 #define MEDIA_BASE_MEDIA_TRACK_H_
 
 #include <string>
 
 #include "media/base/media_export.h"
 #include "media/base/stream_parser.h"
 
 namespace media {
+class DemuxerStream;

[xhwang, 2016/06/09 06:06:02]

Why is this needed?

[servolk, 2016/06/09 19:14:46]

Not needed, leftover from earlier prototyping. Removed.

 
 class MEDIA_EXPORT MediaTrack {
  public:
   enum Type { Text, Audio, Video };
+  using TrackId = std::string;

[xhwang, 2016/06/09 06:06:02]

Will it work if s/Trackid/Id? MediaTrack::TrackId seems redundant. Also Id is
consistent with id() and setId().

[servolk, 2016/06/09 19:14:46]

Done.

   MediaTrack(Type type,
              StreamParser::TrackId byteStreamTrackId,
              const std::string& kind,
              const std::string& label,
              const std::string& lang);
   ~MediaTrack();
 
   Type type() const { return type_; }
 
   StreamParser::TrackId byteStreamTrackId() const { return byteStreamTrackId_; }
   const std::string& kind() const { return kind_; }
   const std::string& label() const { return label_; }
   const std::string& language() const { return language_; }
 
+  TrackId id() const;
+  void setId(TrackId id);

[xhwang, 2016/06/09 06:06:02]

set_id()

[servolk, 2016/06/09 19:14:46]

Done.

+
  private:
   Type type_;
   StreamParser::TrackId byteStreamTrackId_;

[xhwang, 2016/06/09 06:06:02]

nit: use lower_cast instead of CamelCase

[servolk, 2016/06/09 19:14:46]

Done.

   std::string kind_;
   std::string label_;
   std::string language_;

[xhwang, 2016/06/09 06:06:02]

Can you add comments about what these fields are? What are the expected values?
Why these have to be string instead of enums?

[servolk, 2016/06/09 19:14:46]

Done.

+  TrackId id_;

[xhwang, 2016/06/09 06:06:02]

What's the requirement on the uniqueness of the track id? Is it sufficient to
have unique track IDs in one media element?

[xhwang, 2016/06/09 06:06:02]

Can you comment about the difference b/w byteStreamTrackId_ and id_?

[servolk, 2016/06/09 19:14:46]

IIUC these need to be unique in the scope of a single media element. But for
some reason these were made unique in the scope of a single process, since blink
media track id generation used a global (static) counter (see
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/html/trac...).
I'll make the track id generation to be the same in ChunkDemuxer for now, to
avoid any potential issues. But we can reconsider this later.

[servolk, 2016/06/09 19:14:46]

Done.

 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MEDIA_TRACK_H_