How can I change the default Codec used in WebRTC?

In WebRTC, codecs handle the compression and decompression of media content, typically including video and audio streams. Modifying the default codecs can optimize performance and compatibility based on application requirements. Below are the steps to modify the default codecs in WebRTC along with relevant examples:

1. Determine the Available Codec List

First, you need to retrieve the list of codecs supported by WebRTC. This step typically involves calling APIs to enumerate all supported codecs.

Example:

javascript
let pc = new RTCPeerConnection();

pc.createOffer({offerToReceiveAudio: true, offerToReceiveVideo: true})
  .then(offer => pc.setLocalDescription(offer))
  .then(() => {
    let codecs = RTCRtpSender.getCapabilities('video').codecs;
    console.log(codecs);
  });

2. Select and Set Preferred Codecs

After obtaining the codec list, you can choose suitable codecs based on your requirements. Common selection criteria include bandwidth consumption, codec quality, and latency factors.

Example: Suppose you need to set VP8 as the default video codec; this can be achieved by modifying the SDP (Session Description Protocol).

javascript
pc.createOffer().then(offer => {
  let sdp = offer.sdp;

  // Extract VP8 codec information
  let vp8Regex = /a=rtpmap:(\d+) VP8\/\d+/;
  let vp8Codec = sdp.match(vp8Regex);

  // If VP8 codec is found, set it as preferred
  if (vp8Codec) {
    let vp8PayloadType = vp8Codec[1];
    sdp = sdp.replace(/a=rtpmap:\d+ (VP8\/\d+)/g, '');
    sdp = sdp.replace(vp8Regex, 'a=rtpmap:$1 $2\na=rtpmap:' + vp8PayloadType + ' $2');

    // Reconfigure the SDP
    pc.setLocalDescription(new RTCSessionDescription({
      type: 'offer',
      sdp: sdp
    }));
  }
});

3. Verify the Modified Settings

After setting up, you need to conduct actual communication tests to verify if the codec settings are effective and observe if communication quality has improved.

Notes:

• Modifying codec settings may affect WebRTC compatibility; ensure testing across various environments.
• Some codecs may require payment of licensing fees due to patent issues; confirm legal permissions before use.
• Always negotiate with the remote peer to confirm, as the remote peer must also support the same codecs.

By following these steps, you can flexibly modify and select the most suitable WebRTC codecs based on application requirements.