getcommoncapabilities.js

/*
 *  Copyright (c) 2018 rtcpeerconnection-shim authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree.
 */
'use strict';

// Determines the intersection of local and remote capabilities.
module.exports = function(localCapabilities, remoteCapabilities) {
  var commonCapabilities = {
    codecs: [],
    headerExtensions: [],
    fecMechanisms: []
  };

  var findCodecByPayloadType = function(pt, codecs) {
    pt = parseInt(pt, 10);
    for (var i = 0; i < codecs.length; i++) {
      if (codecs[i].payloadType === pt ||
          codecs[i].preferredPayloadType === pt) {
        return codecs[i];
      }
    }
  };

  var rtxCapabilityMatches = function(lRtx, rRtx, lCodecs, rCodecs) {
    var lCodec = findCodecByPayloadType(lRtx.parameters.apt, lCodecs);
    var rCodec = findCodecByPayloadType(rRtx.parameters.apt, rCodecs);
    return lCodec && rCodec &&
        lCodec.name.toLowerCase() === rCodec.name.toLowerCase();
  };

  localCapabilities.codecs.forEach(function(lCodec) {
    for (var i = 0; i < remoteCapabilities.codecs.length; i++) {
      var rCodec = remoteCapabilities.codecs[i];
      if (lCodec.name.toLowerCase() === rCodec.name.toLowerCase() &&
          lCodec.clockRate === rCodec.clockRate) {
        if (lCodec.name.toLowerCase() === 'rtx' &&
            lCodec.parameters && rCodec.parameters.apt) {
          // for RTX we need to find the local rtx that has a apt
          // which points to the same local codec as the remote one.
          if (!rtxCapabilityMatches(lCodec, rCodec,
            localCapabilities.codecs, remoteCapabilities.codecs)) {
            continue;
          }
        }
        rCodec = JSON.parse(JSON.stringify(rCodec)); // deepcopy
        // number of channels is the highest common number of channels
        rCodec.numChannels = Math.min(lCodec.numChannels,
          rCodec.numChannels);
        // push rCodec so we reply with offerer payload type
        commonCapabilities.codecs.push(rCodec);

        // determine common feedback mechanisms
        rCodec.rtcpFeedback = rCodec.rtcpFeedback.filter(function(fb) {
          for (var j = 0; j < lCodec.rtcpFeedback.length; j++) {
            if (lCodec.rtcpFeedback[j].type === fb.type &&
                lCodec.rtcpFeedback[j].parameter === fb.parameter) {
              return true;
            }
          }
          return false;
        });
        // FIXME: also need to determine .parameters
        //  see https://github.com/openpeer/ortc/issues/569
        break;
      }
    }
  });

  localCapabilities.headerExtensions.forEach(function(lHeaderExtension) {
    for (var i = 0; i < remoteCapabilities.headerExtensions.length;
      i++) {
      var rHeaderExtension = remoteCapabilities.headerExtensions[i];
      if (lHeaderExtension.uri === rHeaderExtension.uri) {
        commonCapabilities.headerExtensions.push(rHeaderExtension);
        break;
      }
    }
  });

  // FIXME: fecMechanisms
  return commonCapabilities;
};