text: // CodecsHandler.js
  
  var CodecsHandler = (function() {
      // use "RTCRtpTransceiver.setCodecPreferences"
      function preferCodec(sdp, codecName) {
          var info = splitLines(sdp);
  
          if (!info.videoCodecNumbers) {
              return sdp;
          }
  
          if (codecName === 'vp8' && info.vp8LineNumber === info.videoCodecNumbers[0]) {
              return sdp;
          }
  
          if (codecName === 'vp9' && info.vp9LineNumber === info.videoCodecNumbers[0]) {
              return sdp;
          }
  
          if (codecName === 'h264' && info.h264LineNumber === info.videoCodecNumbers[0]) {
              return sdp;
          }
  
          sdp = preferCodecHelper(sdp, codecName, info);
  
          return sdp;
      }
  
      function preferCodecHelper(sdp, codec, info, ignore) {
          var preferCodecNumber = '';
  
          if (codec === 'vp8') {
              if (!info.vp8LineNumber) {
                  return sdp;
              }
              preferCodecNumber = info.vp8LineNumber;
          }
  
          if (codec === 'vp9') {
              if (!info.vp9LineNumber) {
                  return sdp;
              }
              preferCodecNumber = info.vp9LineNumber;
          }
  
          if (codec === 'h264') {
              if (!info.h264LineNumber) {
                  return sdp;
              }
  
              preferCodecNumber = info.h264LineNumber;
          }
  
          var newLine = info.videoCodecNumbersOriginal.split('SAVPF')[0] + 'SAVPF ';
  
          var newOrder = [preferCodecNumber];
  
          if (ignore) {
              newOrder = [];
          }
  
          info.videoCodecNumbers.forEach(function(codecNumber) {
              if (codecNumber === preferCodecNumber) return;
              newOrder.push(codecNumber);
          });
  
          newLine += newOrder.join(' ');
  
          sdp = sdp.replace(info.videoCodecNumbersOriginal, newLine);
          return sdp;
      }
  
      function splitLines(sdp) {
          var info = {};
          sdp.split('\n').forEach(function(line) {
              if (line.indexOf('m=video') === 0) {
                  info.videoCodecNumbers = [];
                  line.split('SAVPF')[1].split(' ').forEach(function(codecNumber) {
                      codecNumber = codecNumber.trim();
                      if (!codecNumber || !codecNumber.length) return;
                      info.videoCodecNumbers.push(codecNumber);
                      info.videoCodecNumbersOriginal = line;
                  });
              }
  
              if (line.indexOf('VP8/90000') !== -1 && !info.vp8LineNumber) {
                  info.vp8LineNumber = line.replace('a=rtpmap:', '').split(' ')[0];
              }
  
              if (line.indexOf('VP9/90000') !== -1 && !info.vp9LineNumber) {
                  info.vp9LineNumber = line.replace('a=rtpmap:', '').split(' ')[0];
              }
  
              if (line.indexOf('H264/90000') !== -1 && !info.h264LineNumber) {
                  info.h264LineNumber = line.replace('a=rtpmap:', '').split(' ')[0];
              }
          });
  
          return info;
      }
  
      function removeVPX(sdp) {
          var info = splitLines(sdp);
  
          // last parameter below means: ignore these codecs
          sdp = preferCodecHelper(sdp, 'vp9', info, true);
          sdp = preferCodecHelper(sdp, 'vp8', info, true);
  
          return sdp;
      }
  
      function disableNACK(sdp) {
          if (!sdp || typeof sdp !== 'string') {
              throw 'Invalid arguments.';
          }
  
          sdp = sdp.replace('a=rtcp-fb:126 nack\r\n', '');
          sdp = sdp.replace('a=rtcp-fb:126 nack pli\r\n', 'a=rtcp-fb:126 pli\r\n');
          sdp = sdp.replace('a=rtcp-fb:97 nack\r\n', '');
          sdp = sdp.replace('a=rtcp-fb:97 nack pli\r\n', 'a=rtcp-fb:97 pli\r\n');
  
          return sdp;
      }
  
      function prioritize(codecMimeType, peer) {
          if (!peer || !peer.getSenders || !peer.getSenders().length) {
              return;
          }
  
          if (!codecMimeType || typeof codecMimeType !== 'string') {
              throw 'Invalid arguments.';
          }
  
          peer.getSenders().forEach(function(sender) {
              var params = sender.getParameters();
              for (var i = 0; i < params.codecs.length; i++) {
                  if (params.codecs[i].mimeType == codecMimeType) {
                      params.codecs.unshift(params.codecs.splice(i, 1));
                      break;
                  }
              }
              sender.setParameters(params);
          });
      }
  
      function removeNonG722(sdp) {
          return sdp.replace(/m=audio ([0-9]+) RTP\/SAVPF ([0-9 ]*)/g, 'm=audio $1 RTP\/SAVPF 9');
      }
  
      function setBAS(sdp, bandwidth, isScreen) {
          if (!bandwidth) {
              return sdp;
          }
  
          if (typeof isFirefox !== 'undefined' && isFirefox) {
              return sdp;
          }
  
          if (isScreen) {
              if (!bandwidth.screen) {
                  console.warn('It seems that you are not using bandwidth for screen. Screen sharing is expected to fail.');
              } else if (bandwidth.screen < 300) {
                  console.warn('It seems that you are using wrong bandwidth value for screen. Screen sharing is expected to fail.');
              }
          }
  
          // if screen; must use at least 300kbs
          if (bandwidth.screen && isScreen) {
              sdp = sdp.replace(/b=AS([^\r\n]+\r\n)/g, '');
              sdp = sdp.replace(/a=mid:video\r\n/g, 'a=mid:video\r\nb=AS:' + bandwidth.screen + '\r\n');
          }
  
          // remove existing bandwidth lines
          if (bandwidth.audio || bandwidth.video) {
              sdp = sdp.replace(/b=AS([^\r\n]+\r\n)/g, '');
          }
  
          if (bandwidth.audio) {
              sdp = sdp.replace(/a=mid:audio\r\n/g, 'a=mid:audio\r\nb=AS:' + bandwidth.audio + '\r\n');
          }
  
          if (bandwidth.screen) {
              sdp = sdp.replace(/a=mid:video\r\n/g, 'a=mid:video\r\nb=AS:' + bandwidth.screen + '\r\n');
          } else if (bandwidth.video) {
              sdp = sdp.replace(/a=mid:video\r\n/g, 'a=mid:video\r\nb=AS:' + bandwidth.video + '\r\n');
          }
  
          return sdp;
      }
  
      // Find the line in sdpLines that starts with |prefix|, and, if specified,
      // contains |substr| (case-insensitive search).
      function findLine(sdpLines, prefix, substr) {
          return findLineInRange(sdpLines, 0, -1, prefix, substr);
      }
  
      // Find the line in sdpLines[startLine...endLine - 1] that starts with |prefix|
      // and, if specified, contains |substr| (case-insensitive search).
      function findLineInRange(sdpLines, startLine, endLine, prefix, substr) {
          var realEndLine = endLine !== -1 ? endLine : sdpLines.length;
          for (var i = startLine; i < realEndLine; ++i) {
              if (sdpLines[i].indexOf(prefix) === 0) {
                  if (!substr ||
                      sdpLines[i].toLowerCase().indexOf(substr.toLowerCase()) !== -1) {
                      return i;
                  }
              }
          }
          return null;
      }
  
      // Gets the codec payload type from an a=rtpmap:X line.
      function getCodecPayloadType(sdpLine) {
          var pattern = new RegExp('a=rtpmap:(\\d+) \\w+\\/\\d+');
          var result = sdpLine.match(pattern);
          return (result && result.length === 2) ? result[1] : null;
      }
  
      function setVideoBitrates(sdp, params) {
          params = params || {};
          var xgoogle_min_bitrate = params.min;
          var xgoogle_max_bitrate = params.max;
  
          var sdpLines = sdp.split('\r\n');
  
          // VP8
          var vp8Index = findLine(sdpLines, 'a=rtpmap', 'VP8/90000');
          var vp8Payload;
          if (vp8Index) {
              vp8Payload = getCodecPayloadType(sdpLines[vp8Index]);
          }
  
          if (!vp8Payload) {
              return sdp;
          }
  
          var rtxIndex = findLine(sdpLines, 'a=rtpmap', 'rtx/90000');
          var rtxPayload;
          if (rtxIndex) {
              rtxPayload = getCodecPayloadType(sdpLines[rtxIndex]);
          }
  
          if (!rtxIndex) {
              return sdp;
          }
  
          var rtxFmtpLineIndex = findLine(sdpLines, 'a=fmtp:' + rtxPayload.toString());
          if (rtxFmtpLineIndex !== null) {
              var appendrtxNext = '\r\n';
              appendrtxNext += 'a=fmtp:' + vp8Payload + ' x-google-min-bitrate=' + (xgoogle_min_bitrate || '228') + '; x-google-max-bitrate=' + (xgoogle_max_bitrate || '228');
              sdpLines[rtxFmtpLineIndex] = sdpLines[rtxFmtpLineIndex].concat(appendrtxNext);
              sdp = sdpLines.join('\r\n');
          }
  
          return sdp;
      }
  
      function setOpusAttributes(sdp, params) {
          params = params || {};
  
          var sdpLines = sdp.split('\r\n');
  
          // Opus
          var opusIndex = findLine(sdpLines, 'a=rtpmap', 'opus/48000');
          var opusPayload;
          if (opusIndex) {
              opusPayload = getCodecPayloadType(sdpLines[opusIndex]);
          }
  
          if (!opusPayload) {
              return sdp;
          }
  
          var opusFmtpLineIndex = findLine(sdpLines, 'a=fmtp:' + opusPayload.toString());
          if (opusFmtpLineIndex === null) {
              return sdp;
          }
  
          var appendOpusNext = '';
          appendOpusNext += '; stereo=' + (typeof params.stereo != 'undefined' ? params.stereo : '1');
          appendOpusNext += '; sprop-stereo=' + (typeof params['sprop-stereo'] != 'undefined' ? params['sprop-stereo'] : '1');
  
          if (typeof params.maxaveragebitrate != 'undefined') {
              appendOpusNext += '; maxaveragebitrate=' + (params.maxaveragebitrate || 128 * 1024 * 8);
          }
  
          if (typeof params.maxplaybackrate != 'undefined') {
              appendOpusNext += '; maxplaybackrate=' + (params.maxplaybackrate || 128 * 1024 * 8);
          }
  
          if (typeof params.cbr != 'undefined') {
              appendOpusNext += '; cbr=' + (typeof params.cbr != 'undefined' ? params.cbr : '1');
          }
  
          if (typeof params.useinbandfec != 'undefined') {
              appendOpusNext += '; useinbandfec=' + params.useinbandfec;
          }
  
          if (typeof params.usedtx != 'undefined') {
              appendOpusNext += '; usedtx=' + params.usedtx;
          }
  
          if (typeof params.maxptime != 'undefined') {
              appendOpusNext += '\r\na=maxptime:' + params.maxptime;
          }
  
          sdpLines[opusFmtpLineIndex] = sdpLines[opusFmtpLineIndex].concat(appendOpusNext);
  
          sdp = sdpLines.join('\r\n');
          return sdp;
      }
  
      // forceStereoAudio => via webrtcexample.com
      // requires getUserMedia => echoCancellation:false
      function forceStereoAudio(sdp) {
          var sdpLines = sdp.split('\r\n');
          var fmtpLineIndex = null;
          for (var i = 0; i < sdpLines.length; i++) {
              if (sdpLines[i].search('opus/48000') !== -1) {
                  var opusPayload = extractSdp(sdpLines[i], /:(\d+) opus\/48000/i);
                  break;
              }
          }
          for (var i = 0; i < sdpLines.length; i++) {
              if (sdpLines[i].search('a=fmtp') !== -1) {
                  var payload = extractSdp(sdpLines[i], /a=fmtp:(\d+)/);
                  if (payload === opusPayload) {
                      fmtpLineIndex = i;
                      break;
                  }
              }
          }
          if (fmtpLineIndex === null) return sdp;
          sdpLines[fmtpLineIndex] = sdpLines[fmtpLineIndex].concat('; stereo=1; sprop-stereo=1');
          sdp = sdpLines.join('\r\n');
          return sdp;
      }
  
      return {
          removeVPX: removeVPX,
          disableNACK: disableNACK,
          prioritize: prioritize,
          removeNonG722: removeNonG722,
          setApplicationSpecificBandwidth: function(sdp, bandwidth, isScreen) {
              return setBAS(sdp, bandwidth, isScreen);
          },
          setVideoBitrates: function(sdp, params) {
              return setVideoBitrates(sdp, params);
          },
          setOpusAttributes: function(sdp, params) {
              return setOpusAttributes(sdp, params);
          },
          preferVP9: function(sdp) {
              return preferCodec(sdp, 'vp9');
          },
          preferCodec: preferCodec,
          forceStereoAudio: forceStereoAudio
      };
  })();
  
  // backward compatibility
  window.BandwidthHandler = CodecsHandler;
  