我正在使用Webrtc视频流。-(RTCMediaConstraints*)defaultMediaStreamConstraints{NSArray*mandatoryConstraints=@[[[RTCPairalloc]initWithKey:@"maxWidth"value:@"640"],[[RTCPairalloc]initWithKey:@"maxHeight"value:@"480"],[[RTCPairalloc]initWithKey:@"maxFrameRate"value:@"15"],];NSArray*optionalConstraints=@[];RTC