Functional and pure helper to assure video comes first on SDP media lines (tho not so pragmatic). Forked from: https://gist.github.com/edolix/73b2e085104250691a421b8f3678c86c

sdp-handler.js

export function reorderSdpMediaLines(sdp) {
  const lineBreaker = '\r\n';
  const parsed = sdp.split(lineBreaker).reduce((parser, line) => {
    const reading = (line.startsWith('m=video') && 'video')
      || (line.startsWith('m=audio') && 'audio')
      || parser.reading;

    if (line === '') {
      return parser;
    }

    if (reading === 'video') {
      return { ...parser, reading, videoLines: [...parser.videoLines, line] };
    }

    if (reading === 'audio') {
      return { ...parser, reading, audioLines: [...parser.audioLines, line] };
    }

    return { ...parser, reading, otherLines: [...parser.otherLines, line] };
  }, {
    reading: '',
    videoLines: [],
    audioLines: [],
    otherLines: [],
  });

  const resultingLines = [
    ...parsed.otherLines,
    ...parsed.videoLines,
    ...parsed.audioLines,
    '',
  ];

  return resultingLines.join(lineBreaker);
}

sdp-handler.test.js

import { reorderSdpMediaLines } from './sdp-handler';

const SDP_VIDEO_FIRST = 'v=0\r\no=mozilla...THIS_IS_SDPARTA-64.0 6615912393115535091 0 IN IP4 0.0.0.0\r\ns=-\r\nt=0 0\r\na=sendrecv\r\na=fingerprint:sha-256 39:FD:F3:EC:58:BB:E0:FF:C4:A9:F0:D8:B6:89:B6:2D:16:F4:FB:45:2E:36:2F:C4:A5:EA:8C:6C:20:E7:98:7D\r\na=group:BUNDLE 0 1\r\na=ice-options:trickle\r\na=msid-semantic:WMS *\r\nm=video 33831 UDP/TLS/RTP/SAVPF 120 121 126 97\r\nc=IN IP4 172.16.19.165\r\na=candidate:0 1 UDP 2122252543 172.16.19.165 33831 typ host\r\na=candidate:1 1 UDP 2122187007 172.17.0.1 51764 typ host\r\na=candidate:2 1 TCP 2105524479 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 1 TCP 2105458943 172.17.0.1 9 typ host tcptype active\r\na=candidate:0 2 UDP 2122252542 172.16.19.165 36827 typ host\r\na=candidate:1 2 UDP 2122187006 172.17.0.1 41928 typ host\r\na=candidate:2 2 TCP 2105524478 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 2 TCP 2105458942 172.17.0.1 9 typ host tcptype active\r\na=sendrecv\r\na=end-of-candidates\r\na=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=extmap:4 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time\r\na=extmap:5 urn:ietf:params:rtp-hdrext:toffset\r\na=fmtp:126 profile-level-id=42e01f;level-asymmetry-allowed=1;packetization-mode=1\r\na=fmtp:97 profile-level-id=42e01f;level-asymmetry-allowed=1\r\na=fmtp:120 max-fs=12288;max-fr=60\r\na=fmtp:121 max-fs=12288;max-fr=60\r\na=ice-pwd:c3068c1ae5cf4748605b9795f133a14f\r\na=ice-ufrag:ff542923\r\na=mid:0\r\na=msid:{812eca7b-e12e-45b0-840f-b2d6a2e83e47} {dcfb360f-0b24-4005-b9a9-bcaf06ac7bda}\r\na=rtcp:36827 IN IP4 172.16.19.165\r\na=rtcp-fb:120 nack\r\na=rtcp-fb:120 nack pli\r\na=rtcp-fb:120 ccm fir\r\na=rtcp-fb:120 goog-remb\r\na=rtcp-fb:121 nack\r\na=rtcp-fb:121 nack pli\r\na=rtcp-fb:121 ccm fir\r\na=rtcp-fb:121 goog-remb\r\na=rtcp-fb:126 nack\r\na=rtcp-fb:126 nack pli\r\na=rtcp-fb:126 ccm fir\r\na=rtcp-fb:126 goog-remb\r\na=rtcp-fb:97 nack\r\na=rtcp-fb:97 nack pli\r\na=rtcp-fb:97 ccm fir\r\na=rtcp-fb:97 goog-remb\r\na=rtcp-mux\r\na=rtpmap:120 VP8/90000\r\na=rtpmap:121 VP9/90000\r\na=rtpmap:126 H264/90000\r\na=rtpmap:97 H264/90000\r\na=setup:actpass\r\na=ssrc:3497616421 cname:{5daee4d9-07ea-4b59-a411-6c68c04d6e71}\r\nm=audio 58701 UDP/TLS/RTP/SAVPF 109 9 0 8 101\r\nc=IN IP4 172.16.19.165\r\na=candidate:0 1 UDP 2122252543 172.16.19.165 58701 typ host\r\na=candidate:1 1 UDP 2122187007 172.17.0.1 51013 typ host\r\na=candidate:2 1 TCP 2105524479 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 1 TCP 2105458943 172.17.0.1 9 typ host tcptype active\r\na=candidate:0 2 UDP 2122252542 172.16.19.165 48918 typ host\r\na=candidate:1 2 UDP 2122187006 172.17.0.1 50769 typ host\r\na=candidate:2 2 TCP 2105524478 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 2 TCP 2105458942 172.17.0.1 9 typ host tcptype active\r\na=sendrecv\r\na=end-of-candidates\r\na=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level\r\na=extmap:2/recvonly urn:ietf:params:rtp-hdrext:csrc-audio-level\r\na=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=fmtp:109 maxplaybackrate=48000;stereo=1;useinbandfec=1\r\na=fmtp:101 0-15\r\na=ice-pwd:c3068c1ae5cf4748605b9795f133a14f\r\na=ice-ufrag:ff542923\r\na=mid:1\r\na=msid:{812eca7b-e12e-45b0-840f-b2d6a2e83e47} {3083ce40-71a5-4d08-9928-2ca7cbd2ffe4}\r\na=rtcp:48918 IN IP4 172.16.19.165\r\na=rtcp-mux\r\na=rtpmap:109 opus/48000/2\r\na=rtpmap:9 G722/8000/1\r\na=rtpmap:0 PCMU/8000\r\na=rtpmap:8 PCMA/8000\r\na=rtpmap:101 telephone-event/8000\r\na=setup:actpass\r\na=ssrc:4225865926 cname:{5daee4d9-07ea-4b59-a411-6c68c04d6e71}\r\n';
const SDP_AUDIO_FIRST = 'v=0\r\no=mozilla...THIS_IS_SDPARTA-64.0 6615912393115535091 0 IN IP4 0.0.0.0\r\ns=-\r\nt=0 0\r\na=sendrecv\r\na=fingerprint:sha-256 39:FD:F3:EC:58:BB:E0:FF:C4:A9:F0:D8:B6:89:B6:2D:16:F4:FB:45:2E:36:2F:C4:A5:EA:8C:6C:20:E7:98:7D\r\na=group:BUNDLE 0 1\r\na=ice-options:trickle\r\na=msid-semantic:WMS *\r\nm=audio 58701 UDP/TLS/RTP/SAVPF 109 9 0 8 101\r\nc=IN IP4 172.16.19.165\r\na=candidate:0 1 UDP 2122252543 172.16.19.165 58701 typ host\r\na=candidate:1 1 UDP 2122187007 172.17.0.1 51013 typ host\r\na=candidate:2 1 TCP 2105524479 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 1 TCP 2105458943 172.17.0.1 9 typ host tcptype active\r\na=candidate:0 2 UDP 2122252542 172.16.19.165 48918 typ host\r\na=candidate:1 2 UDP 2122187006 172.17.0.1 50769 typ host\r\na=candidate:2 2 TCP 2105524478 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 2 TCP 2105458942 172.17.0.1 9 typ host tcptype active\r\na=sendrecv\r\na=end-of-candidates\r\na=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level\r\na=extmap:2/recvonly urn:ietf:params:rtp-hdrext:csrc-audio-level\r\na=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=fmtp:109 maxplaybackrate=48000;stereo=1;useinbandfec=1\r\na=fmtp:101 0-15\r\na=ice-pwd:c3068c1ae5cf4748605b9795f133a14f\r\na=ice-ufrag:ff542923\r\na=mid:1\r\na=msid:{812eca7b-e12e-45b0-840f-b2d6a2e83e47} {3083ce40-71a5-4d08-9928-2ca7cbd2ffe4}\r\na=rtcp:48918 IN IP4 172.16.19.165\r\na=rtcp-mux\r\na=rtpmap:109 opus/48000/2\r\na=rtpmap:9 G722/8000/1\r\na=rtpmap:0 PCMU/8000\r\na=rtpmap:8 PCMA/8000\r\na=rtpmap:101 telephone-event/8000\r\na=setup:actpass\r\na=ssrc:4225865926 cname:{5daee4d9-07ea-4b59-a411-6c68c04d6e71}\r\nm=video 33831 UDP/TLS/RTP/SAVPF 120 121 126 97\r\nc=IN IP4 172.16.19.165\r\na=candidate:0 1 UDP 2122252543 172.16.19.165 33831 typ host\r\na=candidate:1 1 UDP 2122187007 172.17.0.1 51764 typ host\r\na=candidate:2 1 TCP 2105524479 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 1 TCP 2105458943 172.17.0.1 9 typ host tcptype active\r\na=candidate:0 2 UDP 2122252542 172.16.19.165 36827 typ host\r\na=candidate:1 2 UDP 2122187006 172.17.0.1 41928 typ host\r\na=candidate:2 2 TCP 2105524478 172.16.19.165 9 typ host tcptype active\r\na=candidate:3 2 TCP 2105458942 172.17.0.1 9 typ host tcptype active\r\na=sendrecv\r\na=end-of-candidates\r\na=extmap:3 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=extmap:4 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time\r\na=extmap:5 urn:ietf:params:rtp-hdrext:toffset\r\na=fmtp:126 profile-level-id=42e01f;level-asymmetry-allowed=1;packetization-mode=1\r\na=fmtp:97 profile-level-id=42e01f;level-asymmetry-allowed=1\r\na=fmtp:120 max-fs=12288;max-fr=60\r\na=fmtp:121 max-fs=12288;max-fr=60\r\na=ice-pwd:c3068c1ae5cf4748605b9795f133a14f\r\na=ice-ufrag:ff542923\r\na=mid:0\r\na=msid:{812eca7b-e12e-45b0-840f-b2d6a2e83e47} {dcfb360f-0b24-4005-b9a9-bcaf06ac7bda}\r\na=rtcp:36827 IN IP4 172.16.19.165\r\na=rtcp-fb:120 nack\r\na=rtcp-fb:120 nack pli\r\na=rtcp-fb:120 ccm fir\r\na=rtcp-fb:120 goog-remb\r\na=rtcp-fb:121 nack\r\na=rtcp-fb:121 nack pli\r\na=rtcp-fb:121 ccm fir\r\na=rtcp-fb:121 goog-remb\r\na=rtcp-fb:126 nack\r\na=rtcp-fb:126 nack pli\r\na=rtcp-fb:126 ccm fir\r\na=rtcp-fb:126 goog-remb\r\na=rtcp-fb:97 nack\r\na=rtcp-fb:97 nack pli\r\na=rtcp-fb:97 ccm fir\r\na=rtcp-fb:97 goog-remb\r\na=rtcp-mux\r\na=rtpmap:120 VP8/90000\r\na=rtpmap:121 VP9/90000\r\na=rtpmap:126 H264/90000\r\na=rtpmap:97 H264/90000\r\na=setup:actpass\r\na=ssrc:3497616421 cname:{5daee4d9-07ea-4b59-a411-6c68c04d6e71}\r\n';

describe('reorderSdpMediaLines: helper to assure video comes first on sdp media lines', function () {
  it('reorder sdp media lines for video to come first', function() {
    expect(reorderSdpMediaLines(SDP_AUDIO_FIRST)).toEqual(SDP_VIDEO_FIRST);
  });

  it('if video already comes first, do nothing', function() {
    expect(reorderSdpMediaLines(SDP_VIDEO_FIRST)).toEqual(SDP_VIDEO_FIRST);
  });
});