音視頻學(xué)習(xí)筆記 - WebRTC協(xié)商過程
RTCPeerConnection
它是WebRTC中最關(guān)鍵的一個類, 端到端間的媒體協(xié)商就是基于該類對象實(shí)現(xiàn)的.
...
var pcConfig = null;
var pc = new RTCPeerConnection(pcConfig);
...
協(xié)商過程
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Offer
在雙方通訊時, 呼叫發(fā)送的SDP消息稱為Offer.
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Answer
在雙方通訊時, 被呼叫方發(fā)送的SDP消息稱為Answer.
時序圖
Screen Shot 2020-03-08 at 8.35.33 PM.png
- 呼叫方創(chuàng)建Offer類型的SDP消息, 調(diào)用setLocalDescription方法將該Offer保存到本地Local域, 再通過信令將Offer發(fā)送給被呼叫方.
- 被呼叫方收到Offer類型的SDP消息后, 調(diào)用setRemoteDescription方法將Offer保存到它的Remote域.
- 被呼叫方創(chuàng)建Answer類型的SDP消息, 調(diào)用setLocalDescription方法將Answer類型的SDP消息保存到本地的Local域.
- 被呼叫方將Answer消息通過信令發(fā)送給呼叫方.
- 呼叫方收到Answer類型的消息后, 調(diào)用setRemoteDescription方法, 將Answer保存到它的Remote域.
當(dāng)通訊雙方拿到彼此的SDP消息后, 就可以進(jìn)行媒體協(xié)商了.
代碼實(shí)現(xiàn)
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呼叫方創(chuàng)建Offer
function doCall() { console.log('Sending offer to peer'); pc.createOffer(setLocalAndSendMessage, handleCreateOfferError); } function setLocalAndSendMessage(sessionDescription) { pc.setLocalDescription(sessionDescription); sendMessage(sessionDescription); } socket.on('message', function(message) { ... } else if (message.type === 'answer') { pc.setRemoteDescription(new RTCSessionDescription(message)); } else if (...) { ... } .... });
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被呼叫方收到Offer
socket.on('message', function(message) { ... } else if (message.type === 'offer') { pc.setRemoteDescription(new RTCSessionDescription(message)); doAnswer(); } else if (...) { ... } .... }); function doAnswer() { pc.createAnswer().then( setLocalAndSendMessage, onCreateSessionDescriptionError ); }
