gistfile1.js

var lines = desc.sdp.split("\r\n");
var ssrc, ssrc_fid, msid;
for (var i=0; i<lines.length; i++) {
    var fid = lines[i].match(/a=ssrc-group:FID (\d+) (\d+)/);
    if (fid) {
        ssrc = fid[1];
        ssrc_fid = fid[2];
        lines.splice(i, 1); i--;
        continue;
    }
    if (lines[i].indexOf("m=video 1 RTP/SAVPF") == 0) {
        lines[i] = 'm=video 1 RTP/SAVPF 100';
    }
    if (lines[i] == 'a=rtpmap:116 red/90000') {
        lines.splice(i, 1); i--;
        continue;
    }
    if (lines[i] == 'a=rtpmap:117 ulpfec/90000') {
        lines.splice(i, 1); i--;
        continue;
    }
    if (lines[i] == 'a=rtpmap:96 rtx/90000') {
        lines.splice(i, 1); i--;
        continue;
    }
    if (lines[i] == 'a=fmtp:96 apt=100') {
        lines.splice(i, 1); i--;
        continue;
    }
    if (ssrc) {
        var match = lines[i].match('a=ssrc:' + ssrc + ' msid:(.+)')
        if (match) {
            msid = match[1];
        }
        if (lines[i].indexOf('a=ssrc:' + ssrc_fid) === 0) {
            lines.splice(i, 1); i--;
            continue;
        }
        if (lines[i].indexOf('a=ssrc:' + ssrc) === 0) {
            lines.splice(i, 1); i--;
            continue;
        }
    }
    if (lines[i].length == 0) {
        lines.splice(i, 1); i--;
        continue;
    }
}

lines.push('a=ssrc-group:SIM ' + ssrc +' 4084008107 2771988318')
lines.push('a=ssrc:' + ssrc +' cname:localCname')
lines.push('a=ssrc:' + ssrc +' msid:' + msid)
lines.push('a=ssrc:4084008107 cname:localCname')
lines.push('a=ssrc:4084008107 msid:' + msid)
lines.push('a=ssrc:2771988318 cname:localCname')
lines.push('a=ssrc:2771988318 msid:' + msid)
lines.push('')