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Fix extractRtpCapabilities() mixing up audio and video RTP header extensions #397

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Merged
ibc merged 1 commit into from
Oct 21, 2026
Merged

Fix extractRtpCapabilities() mixing up audio and video RTP header extensions #397

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16 changes: 13 additions & 3 deletions src/handlers/sdp/commonUtils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,15 @@ export function extractRtpCapabilities({
}): RtpCapabilities {
// Map of RtpCodecParameters indexed by payload type.
const codecsMap: Map<number, RtpCodecCapability> = new Map();
// Map of RtpHeaderExtensions indexed by preferred id.
const headerExtensionMap: Map<number, RtpHeaderExtension> = new Map();
// Map of RtpHeaderExtensions indexed by kind and preferred id.
//
// NOTE: It must be indexed by kind and id rather than just by id. Since all
// m= sections are bundled, the browser gives the same id to a given extension
// in every m= section that supports it, so indexing just by id would collapse
// the audio and the video entry of such an extension into a single one with
// the kind of the last processed m= section, making the extension vanish for
// the other kind.
const headerExtensionMap: Map<string, RtpHeaderExtension> = new Map();

for (const m of sdpObject.media) {
const kind = m.type;
Expand Down Expand Up @@ -122,7 +129,10 @@ export function extractRtpCapabilities({
preferredId: ext.value,
};

headerExtensionMap.set(headerExtension.preferredId, headerExtension);
headerExtensionMap.set(
`${kind}:${headerExtension.preferredId}`,
headerExtension
);
}
}

Expand Down
61 changes: 61 additions & 0 deletions src/test/test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,9 @@
*/

import { FakeMediaStreamTrack } from 'fake-mediastreamtrack';
import * as sdpTransform from 'sdp-transform';
import * as mediasoupClient from '../index';
import * as sdpCommonUtils from '../handlers/sdp/commonUtils';
import { UnsupportedError, InvalidStateError } from '../errors';
import * as utils from '../utils';
import type { RtpCapabilities } from '../RtpParameters';
Expand Down Expand Up @@ -1762,3 +1764,62 @@ describe('detectDevice() and detectDeviceAsync() assign proper handler based on
);
}
});

test('sdpCommonUtils.extractRtpCapabilities() does not mix up audio and video extensions sharing the same id', () => {
// NOTE: Since all m= sections are bundled, the browser gives the same id to
// a given RTP header extension in every m= section that supports it (here
// sdes:mid has id 4 in both the audio and the video m= section).
const sdp = [
'v=0',
'o=- 0 0 IN IP4 127.0.0.1',
's=-',
't=0 0',
'a=group:BUNDLE 0 1',
'm=audio 9 UDP/TLS/RTP/SAVPF 111',
'c=IN IP4 0.0.0.0',
'a=mid:0',
'a=sendonly',
'a=rtpmap:111 opus/48000/2',
'a=extmap:1 urn:ietf:params:rtp-hdrext:ssrc-audio-level',
'a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid',
'm=video 9 UDP/TLS/RTP/SAVPF 96',
'c=IN IP4 0.0.0.0',
'a=mid:1',
'a=sendonly',
'a=rtpmap:96 VP8/90000',
'a=extmap:4 urn:ietf:params:rtp-hdrext:sdes:mid',
'a=extmap:13 urn:3gpp:video-orientation',
'',
].join('\r\n');

const rtpCapabilities = sdpCommonUtils.extractRtpCapabilities({
sdpObject: sdpTransform.parse(sdp),
});

expect(rtpCapabilities.headerExtensions).toEqual(
expect.arrayContaining([
{
kind: 'audio',
uri: 'urn:ietf:params:rtp-hdrext:ssrc-audio-level',
preferredId: 1,
},
{
kind: 'audio',
uri: 'urn:ietf:params:rtp-hdrext:sdes:mid',
preferredId: 4,
},
{
kind: 'video',
uri: 'urn:ietf:params:rtp-hdrext:sdes:mid',
preferredId: 4,
},
{
kind: 'video',
uri: 'urn:3gpp:video-orientation',
preferredId: 13,
},
])
);

expect(rtpCapabilities.headerExtensions!.length).toBe(4);
});
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