@webex/ts-sdp

ts-sdp

ts-sdp is a library which allows for parsing, manipulation, and serialization of SDP.

Examples

Parsing

To parse an SDP string, just call the parse method.

const sdp = parse(sdpOffer);

Note: the given SDP string must terminate each line with either \r, \r\n or \n.

Manipulation

Once parsed, the SDP can be manipulated. The model of the parsed object is as follows:

There are munging helper functions available in the munge.ts file. For example:

removeCodec(parsedSdp, 'vp8');
disableRtcpFbValue(parsedSdp, 'goog-remb');

Manipulation can also be done manually:

TODO: more examples

Serialization

When done, the SDP can be serialized to a string like so:

const sdpStr = sdp.toString();

Grammar

The library currently contains much of the RGC4566 grammar, in addition to some additional attributes. Any lines without specific parser implementations are still parsed via the UnknownLine type.

The grammar is extendable to allow for parsing custom attributes. First, a subclass of Line must be defined:

  class CustomLine extends Line {
    value: number;

    private static regex = /^foo:([0-9]+)$/;

    constructor(value: number) {
      super();
      this.value = value;
    }

    static fromSdpLine(line: string): CustomLine | undefined {
      if (!CustomLine.regex.test(line)) {
        return undefined;
      }

      const tokens = line.match(CustomLine.regex) as RegExpMatchArray;
      const value = parseInt(tokens[1], 10);
      return new CustomLine(value);
    }

    toSdpLine(): string {
      return `a=foo:${this.value}`;
    }
  }

Then the parser must be added to the grammar under the appropriate LineType:

DefaultSdpGrammar.addParser('a', CustomLine.fromSdpLine);
// Result will contain a 'CustomLine' instance in whichever SdpBlock the attribute appears.
const result = parse(sdp);

Any implementation of Grammar can also be passed to the parse method:

class MyCustomGrammar extends Grammar {
    ...
}
const myGrammar = new MyCustomGrammar();
const result = parse(sdp, myGrammar);