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Fix mandatory MID header extension negotiation #395

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Fix mandatory MID header extension negotiation #395

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7 changes: 6 additions & 1 deletion src/handlers/ortc/utils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,12 @@ export function applyForcedRtpExtensions(
const uri = extenCap.uri as RtpHeaderExtensionUri;
const enabled: boolean | undefined = forcedRtpExtensions[uri];

if (enabled === true) {
// MID is mandatory when BUNDLE is used and cannot be disabled by this API.
// Some browsers may report it as stopped after negotiation, but reject the
// entire list if that direction is submitted again.
Comment on lines -78 to +80

@ibc ibc Oct 19, 2026 •
edited
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This is an IA written PR. Which is the real evidence behind this IA predictable comment? It clearly looks like if you prompted to the IA agent some statement (what is said in the reported issue ticket) and it just generated a solution assuming that issue is true or normal behavior in some browsers. Is this a bug already reported in libwebrtc?

if (uri === 'urn:ietf:params:rtp-hdrext:sdes:mid') {
extenCap.direction = 'sendrecv';
} else if (enabled === true) {
extenCap.direction = 'sendrecv';
} else if (enabled === false) {
extenCap.direction = 'stopped';
Expand Down
38 changes: 38 additions & 0 deletions src/test/test.ts
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Expand Up @@ -7,6 +7,7 @@ import { FakeMediaStreamTrack } from 'fake-mediastreamtrack';
import * as mediasoupClient from '../index';
import { UnsupportedError, InvalidStateError } from '../errors';
import * as utils from '../utils';
import { applyForcedRtpExtensions } from '../handlers/ortc/utils';
import type { RtpCapabilities } from '../RtpParameters';
import { FakeHandler } from '../handlers/FakeHandler';
import * as fakeParameters from './fakeParameters';
Expand Down Expand Up @@ -1762,3 +1763,40 @@ describe('detectDevice() and detectDeviceAsync() assign proper handler based on
);
}
});

describe('applyForcedRtpExtensions()', () => {
test('keeps the mandatory MID extension enabled when forcing another extension', () => {
const midUri = 'urn:ietf:params:rtp-hdrext:sdes:mid';
const absCaptureTimeUri =
'http://www.webrtc.org/experiments/rtp-hdrext/abs-capture-time';
const capabilities: RTCRtpHeaderExtensionCapability[] = [
{ uri: midUri, direction: 'stopped' },
{ uri: absCaptureTimeUri, direction: 'recvonly' },
];
let submittedCapabilities: RTCRtpHeaderExtensionCapability[] | undefined;
const transceiver = {
getHeaderExtensionsToNegotiate: () => capabilities,
setHeaderExtensionsToNegotiate: (
nextCapabilities: RTCRtpHeaderExtensionCapability[]
) => {
const midExtension = nextCapabilities.find(({ uri }) => uri === midUri);

if (midExtension?.direction !== 'sendrecv') {
throw new Error('Attempted to stop a mandatory extension.');
}

submittedCapabilities = nextCapabilities;
},
} as unknown as RTCRtpTransceiver;

expect(
applyForcedRtpExtensions(transceiver, {
[absCaptureTimeUri]: true,
})
).toBe(true);
expect(submittedCapabilities).toEqual([
{ uri: midUri, direction: 'sendrecv' },
{ uri: absCaptureTimeUri, direction: 'sendrecv' },
]);
});
});