Generate and assign media track ids in demuxers.

media/base/media_tracks.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_TRACKS_H_
 #define MEDIA_BASE_MEDIA_TRACKS_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "media/base/media_export.h"
 #include "media/base/media_track.h"
 
 namespace media {
 
 class AudioDecoderConfig;
 class VideoDecoderConfig;
 
 class MEDIA_EXPORT MediaTracks {
  public:
   using MediaTracksCollection = std::vector<std::unique_ptr<MediaTrack>>;
 
   MediaTracks();
   ~MediaTracks();
 
-  // Callers need to ensure that track id is unique.
-  void AddAudioTrack(const AudioDecoderConfig& config,
-                     StreamParser::TrackId byteStreamTrackId,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
-  // Callers need to ensure that track id is unique.
-  void AddVideoTrack(const VideoDecoderConfig& config,
-                     StreamParser::TrackId byteStreamTrackId,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
+  // Adds a new audio track. The |bytestreamTrackId| must uniquely identify the
+  // track within the bytestream.
+  MediaTrack* AddAudioTrack(const AudioDecoderConfig& config,
+                            StreamParser::TrackId byteStreamTrackId,
+                            const std::string& kind,
+                            const std::string& label,
+                            const std::string& language);
+  // Adds a new video track. The |bytestreamTrackId| must uniquely identify the
+  // track within the bytestream.
+  MediaTrack* AddVideoTrack(const VideoDecoderConfig& config,
+                            StreamParser::TrackId byteStreamTrackId,
+                            const std::string& kind,
+                            const std::string& label,
+                            const std::string& language);
 
   const MediaTracksCollection& tracks() const { return tracks_; }
 
   const AudioDecoderConfig& getAudioConfig(
       StreamParser::TrackId byteStreamTrackId) const;
   const VideoDecoderConfig& getVideoConfig(
       StreamParser::TrackId byteStreamTrackId) const;
 
   // TODO(servolk): These are temporary helpers useful until all code paths are
   // converted to properly handle multiple media tracks.
   const AudioDecoderConfig& getFirstAudioConfig() const;
   const VideoDecoderConfig& getFirstVideoConfig() const;
 
  private:
   MediaTracksCollection tracks_;
   std::map<StreamParser::TrackId, AudioDecoderConfig> audio_configs_;
   std::map<StreamParser::TrackId, VideoDecoderConfig> video_configs_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaTracks);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_MEDIA_TRACKS_H_