From 84cc49aa9c4f996a1d37635e9933cafae4ef6686 Mon Sep 17 00:00:00 2001
From: Joas Schilling <coding@schilljs.com>
Date: Thu, 9 Apr 2026 16:07:31 +0200
Subject: [PATCH] fix(webrtc): Calculate maxBitrates based on HPBs
 maxstreambits

Signed-off-by: Joas Schilling <coding@schilljs.com>
---
 src/utils/signaling.js                        |  8 +++++
 src/utils/webrtc/simplewebrtc/simplewebrtc.js | 30 +++++++++++++++----
 src/utils/webrtc/simplewebrtc/webrtc.js       |  1 +
 3 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/src/utils/signaling.js b/src/utils/signaling.js
index 31526c985d8..c4a190c20ce 100644
--- a/src/utils/signaling.js
+++ b/src/utils/signaling.js
@@ -71,6 +71,7 @@ function Base(settings) {
 	this.signalingConnectionTimeout = null
 	this.signalingConnectionWarning = null
 	this.signalingConnectionError = null
+	this.maxStreamBits = 1048576
 }
 
 Signaling.Base = Base
@@ -1281,6 +1282,13 @@ Signaling.Standalone.prototype.joinCall = function(token, flags, silent, recordi
 
 Signaling.Standalone.prototype.joinResponseReceived = function(data, token) {
 	console.debug('Joined', data, token)
+	if (data.room?.bandwidth?.maxstreambitrate) {
+		const totalBps = data.room.bandwidth.maxstreambitrate
+		if (typeof totalBps === 'number' && totalBps > 0) {
+			this.maxStreamBits = data.room.bandwidth.maxstreambitrate
+		}
+	}
+
 	this.signalingRoomJoined = token
 	if (this.pendingJoinCall && token === this.pendingJoinCall.token) {
 		const pendingJoinCallResolve = this.pendingJoinCall.resolve
diff --git a/src/utils/webrtc/simplewebrtc/simplewebrtc.js b/src/utils/webrtc/simplewebrtc/simplewebrtc.js
index 9af8778cdf6..7bab20793db 100644
--- a/src/utils/webrtc/simplewebrtc/simplewebrtc.js
+++ b/src/utils/webrtc/simplewebrtc/simplewebrtc.js
@@ -8,6 +8,30 @@ import webrtcSupport from 'webrtcsupport'
 import WildEmitter from 'wildemitter'
 import WebRTC from './webrtc.js'
 
+/**
+ * Split totalBps into integer low/medium/high parts with ratio 1:4:16 (total 21 parts).
+ * Returned values are integers. Any remainder from integer division is omitted.
+ *
+ * @param {number} totalBps - Total bandwidth in bps (non-negative number).
+ * @returns {{ low: number, medium: number, high: number }}
+ */
+function splitBandwidthIntegersOmitRemainder(totalBps = 1048576) {
+	if (typeof totalBps !== 'number' || totalBps < 0) {
+		totalBps = 1048576
+	}
+
+	// Divide into 21 parts and distribute them in 2^2 way across the quality levels
+	// Additionally we divide and multiple with 100 but round down in between
+	// to create some safety bits
+	const partValue = Math.floor(totalBps / 21 / 100) * 100
+
+	return {
+		low: partValue,
+		medium: partValue * 4,
+		high: partValue * 16,
+	}
+}
+
 /**
  * @param {object} opts the options object.
  */
@@ -19,11 +43,7 @@ export default function SimpleWebRTC(opts) {
 		debug: false,
 		enableDataChannels: true,
 		enableSimulcast: false,
-		maxBitrates: {
-			high: 900000,
-			medium: 300000,
-			low: 100000,
-		},
+		maxBitrates: splitBandwidthIntegersOmitRemainder(opts.connection?.maxStreamBits),
 		autoRequestMedia: false,
 		receiveMedia: {
 			offerToReceiveAudio: 1,
diff --git a/src/utils/webrtc/simplewebrtc/webrtc.js b/src/utils/webrtc/simplewebrtc/webrtc.js
index 3b443fc33d1..bb6a8fd3938 100644
--- a/src/utils/webrtc/simplewebrtc/webrtc.js
+++ b/src/utils/webrtc/simplewebrtc/webrtc.js
@@ -27,6 +27,7 @@ export default function WebRTC(opts) {
 		},
 		enableDataChannels: true,
 		enableSimulcast: false,
+		// Overwritten by simplewebrtc.js
 		maxBitrates: {
 			high: 900000,
 			medium: 300000,