2.3.1 约束类型_WebRTC技术详解：从0到1构建多人视频会议系统-QQ阅读男生中文历史网

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2.3.1　约束类型

媒体约束包括媒体流约束（MediaStreamConstraints）和媒体轨道约束（MediaTrackCon-straints）。

MediaStreamConstraints的定义如代码清单2-26所示。

代码清单2-26　MediaStreamConstraints的定义

dictionary MediaStreamConstraints {
  (boolean or MediaTrackConstraints) video = false;
  (boolean or MediaTrackConstraints) audio = false;
};

MediaStreamConstraints属性说明如表2-1所示。

表2-1　MediaStreamConstraints属性说明

MediaTrackConstraints的定义如代码清单2-27所示。

代码清单2-27　MediaTrackConstraints的定义

dictionary MediaTrackConstraints : MediaTrackConstraintSet {
  sequence<MediaTrackConstraintSet> advanced;
};

dictionary MediaTrackConstraintSet {
  ConstrainULong width;
  ConstrainULong height;
  ConstrainDouble aspectRatio;
  ConstrainDouble frameRate;
  ConstrainDOMString facingMode;
  ConstrainDOMString resizeMode;
  ConstrainULong sampleRate;
  ConstrainULong sampleSize;
  ConstrainBoolean echoCancellation;
  ConstrainBoolean autoGainControl;
  ConstrainBoolean noiseSuppression;
  ConstrainDouble latency;
  ConstrainULong channelCount;
  ConstrainDOMString deviceId;
  ConstrainDOMString groupId;
};