RTCRtpTransceiver.direction - Web API 接口参考 编辑

The RTCRtpTransceiver property direction is a string which indicates the transceiver's preferred directionality. Its value must be one of the strings defined by the RTCRtpTransceiverDirection enumeration.

The transceiver's current direction is indicated by the currentDirection property.

Syntax

var direction = RTCRtpTransceiver.direction

Value

A DOMString whose value is one of the strings which are a member of the RTCRtpTransceiverDirection enumerated type, indicating the transceiver's preferred direction.

The RTCRtpTransceiverDirection type is an enumeration of string values. Each describes how the transceiver's associated RTCRtpSender and RTCRtpReceiver behave as shown in the table below.

Value	RTCRtpSender behavior	RTCRtpReceiver behavior
"sendrecv"	Offers to send RTP data, and will do so if the other peer accepts the connection and at least one of the sender's encodings is active1.	Offers to receive RTP data, and does so if the other peer accepts.
"sendonly"	Offers to send RTP data, and will do so if the other peer accepts the connection and at least one of the sender's encodings is active1.	Does not offer to receive RTP data and will not do so.
"recvonly"	Does not offer to send RTP data, and will not do so.	Offers to receive RTP data, and will do so if the other peer offers.
"inactive"	Does not offer to send RTP data, and will not do so.	Does not offer to receive RTP data and will not do so.

[1] To determine if a sender has at least one active encoding, the user agent gets its parameters using RTCRtpSender.getParameters(), then looks at the parameters' encodings property; if any of the listed encodings has its active property set to true, the sender has an active encoding.

Exceptions

When setting the value of direction, the following exceptions can occur:

InvalidStateError

Either the receiver's RTCPeerConnection is closed or the RTCRtpReceiver is stopped.

Usage notes

Setting the direction

When you change the value of direction, an InvalidStateError exception will occur if the connection is closed or the receiver is stopped.

If the new value of direction is in fact different from the existing value, renegotiation of the connection is required, so a negotiationneeded event is sent to the RTCPeerConnection.

Effect on offers and answers

The value of direction is used by RTCPeerConnection.createOffer() or RTCPeerConnection.createAnswer() in order to generate the SDP generated by each of those methods. The SDP contains an a-line which specifies the directionality. For example, if the direction is specified as "sendrecv", the corresponding SDP a-line is:

a=sendrecv

Specifications

Specification	Status	Comment
WebRTC 1.0: Real-time Communication Between Browsers RTCRtpTransceiver.direction	Candidate Recommendation

Browser compatibility

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The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• RTCRtpTransceiver.currentDirection