media/base/media_track.h

// Copyright 2016 The Chromium Authors
// 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 "base/types/strong_alias.h"
#include "media/base/media_export.h"
#include "media/base/stream_parser.h"

namespace media {

class MEDIA_EXPORT MediaTrack {
 public:
  enum Type { Text, Audio, Video };
  using Id = base::StrongAlias<class IdTag, std::string>;
  using Kind = base::StrongAlias<class KindTag, std::string>;
  using Label = base::StrongAlias<class LabelTag, std::string>;
  using Language = base::StrongAlias<class LanguageTag, std::string>;
  MediaTrack(Type type,
             StreamParser::TrackId bytestream_track_id,
             const Kind& kind,
             const Label& label,
             const Language& lang);
  ~MediaTrack();

  Type type() const { return type_; }

  StreamParser::TrackId bytestream_track_id() const {
    return bytestream_track_id_;
  }
  const Kind& kind() const { return kind_; }
  const Label& label() const { return label_; }
  const Language& language() const { return language_; }

  Id id() const { return id_; }
  void set_id(Id id) {
    DCHECK(id_.value().empty());
    DCHECK(!id.value().empty());
    id_ = id;
  }

 private:
  Type type_;

  // |bytestream_track_id_| is read from the bytestream and is guaranteed to be
  // unique only within the scope of single bytestream's initialization segment.
  // But we might have multiple bytestreams (MediaSource might have multiple
  // SourceBuffers attached to it, which translates into ChunkDemuxer having
  // multiple SourceBufferStates and multiple bytestreams) or subsequent init
  // segments may redefine the bytestream ids. Thus bytestream track ids are not
  // guaranteed to be unique at the Demuxer and HTMLMediaElement level. So we
  // generate truly unique media track |id_| on the Demuxer level.
  StreamParser::TrackId bytestream_track_id_;
  Id id_;

  // These properties are read from input streams by stream parsers as specified
  // in https://dev.w3.org/html5/html-sourcing-inband-tracks/.
  Kind kind_;
  Label label_;
  Language language_;
};

// Helper for logging.
MEDIA_EXPORT const char* TrackTypeToStr(MediaTrack::Type type);

}  // namespace media

#endif  // MEDIA_BASE_MEDIA_TRACK_H_