export function transformSdp()

in src/js/utils.js [126:197]
58 lines of code
13 McCabe index (conditional complexity)

export function transformSdp(sdp, sdpOptions) {
    var sections = splitSections(sdp);
    for (var i = 1; i < sections.length; i++) {
        var mediaType = getKind(sections[i]);
        var rtpParams = parseRtpParameters(sections[i]);
        // a map from payload type (string) to codec object
        var codecMap = rtpParams.codecs.reduce((map, codec) => {
            map['' + codec.payloadType] = codec;
            return map;
        }, {});
        sections[i] = splitLines(sections[i]).map(line => {
            if (line.startsWith('m=')) {
                // modify m= line if SdpOptions#forceCodec specifies codec for current media type
                if (sdpOptions.forceCodec[mediaType]) {
                    var targetCodecPts = Object.keys(codecMap).filter(pt => !sdpOptions._shouldDeleteCodec(mediaType, codecMap[pt].name));
                    return /.*RTP\/S?AVPF? /.exec(line) + targetCodecPts.join(' ');
                } else {
                    return line;
                }
            } else if (line.startsWith('a=rtpmap:')) {
                var rtpMap = parseRtpMap(line);
                var currentCodec = codecMap[rtpMap.payloadType];

                // remove this codec if SdpOptions#forceCodec specifies a different codec for current media type
                if (sdpOptions._shouldDeleteCodec(mediaType, currentCodec.name)) {
                    return null;
                }
                
                // append a=fmtp line immediately if current codec is OPUS (to explicitly specify OPUS parameters)
                if (currentCodec.name.toUpperCase() === 'OPUS') { 
                    currentCodec.parameters.usedtx = sdpOptions.enableOpusDtx ? "1" : "0";
                    // generate fmtp line immediately after rtpmap line, and remove original fmtp line once we see it
                    return (line + "\r\n" + writeFmtp(currentCodec)).trim();
                } else {
                    return line;
                }
            } else if (line.startsWith('a=fmtp:')) {
                var pt = line.substring('a=fmtp:'.length, line.indexOf(' '));
                var currentCodec = codecMap[pt];// eslint-disable-line no-redeclare

                // remove this codec if SdpOptions#forceCodec specifies a different codec for current media type
                if (sdpOptions._shouldDeleteCodec(mediaType, currentCodec.name)) {
                    return null;
                }

                if (currentCodec.name.toUpperCase() === 'OPUS') {
                    // this is a line for OPUS, remove it because FMTP line is already generated when rtpmap line is processed
                    return null;
                } else {
                    return line;
                }
            } else if (line.startsWith('a=rtcp-fb:')) {
                var pt = line.substring(line.indexOf(':') + 1, line.indexOf(' '));// eslint-disable-line no-redeclare
                var currentCodec = codecMap[pt];// eslint-disable-line no-redeclare

                // remove this codec if SdpOptions#forceCodec specifies a different codec for current media type
                if (sdpOptions._shouldDeleteCodec(mediaType, currentCodec.name)) {
                    return null;
                } else {
                    return line;
                }
            } else {
                return line;
            }
        }).filter(line => line !== null).join('\r\n');

    }
    return {
        sdp: sections.map(section => section.trim()).join('\r\n') + '\r\n',
        mLines: sections.length - 1 // first section is session description, the rest are media descriptions
    };
}