From 39f3ce4a7a453ff95dba8b750600ff4b9390de71 Mon Sep 17 00:00:00 2001
From: Davi Bittencourt <85559208+davibittencourtome@users.noreply.github.com>
Date: Tue, 25 Aug 2026 15:42:28 -0300
Subject: [PATCH] fix: skip duplicate backup codec publish instead of throwing

A duplicate SubscribedQualityUpdate arriving while the backup codec
publication is still in flight (sender not yet attached) re-enters
addSimulcastTrack and crashed the app with
IllegalStateException("VP8 already added!").

Make addSimulcastTrack idempotent: log and return null for an
already-added codec, and bail out of publishAdditionalCodecForTrack so
no duplicate transceiver or AddTrackRequest is created. Mirrors the JS
SDK behavior. Dedup is per track instance, so a track republished after
a reconnect still publishes its backup codec normally.

Fixes #1000
---
 .changeset/idempotent-add-simulcast-track.md  |  5 ++++
 .../room/participant/LocalParticipant.kt      |  5 +++-
 .../android/room/track/LocalVideoTrack.kt     |  5 ++--
 .../LocalParticipantMockE2ETest.kt            | 30 +++++++++++++++++++
 4 files changed, 42 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/idempotent-add-simulcast-track.md

diff --git a/.changeset/idempotent-add-simulcast-track.md b/.changeset/idempotent-add-simulcast-track.md
new file mode 100644
index 000000000..6a429e994
--- /dev/null
+++ b/.changeset/idempotent-add-simulcast-track.md
@@ -0,0 +1,5 @@
+---
+"client-sdk-android": patch
+---
+
+Fix crash when a duplicate SubscribedQualityUpdate requests a backup codec that is already added. addSimulcastTrack now skips the duplicate instead of throwing IllegalStateException ("VP8 already added!"), matching the JS SDK behavior.
diff --git a/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt b/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
index 75ac69c11..619a540c8 100644
--- a/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
+++ b/livekit-android-sdk/src/main/java/io/livekit/android/room/participant/LocalParticipant.kt
@@ -1273,7 +1273,10 @@ internal constructor(
             return
         }
         val (newOptions, newEncodings) = result
-        val simulcastTrack = track.addSimulcastTrack(codec, newEncodings)
+        // A duplicate SubscribedQualityUpdate can request a codec that is already being
+        // published (or mid-publish, before the sender is attached). Treat it as a no-op
+        // instead of throwing, so a repeated update doesn't crash the session.
+        val simulcastTrack = track.addSimulcastTrack(codec, newEncodings) ?: return
 
         val transceiverInit = RtpTransceiverInit(
             RtpTransceiver.RtpTransceiverDirection.SEND_ONLY,
diff --git a/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt b/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
index 358ed6fb9..074e2ce08 100644
--- a/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
+++ b/livekit-android-sdk/src/main/java/io/livekit/android/room/track/LocalVideoTrack.kt
@@ -430,9 +430,10 @@ constructor(
         return newCodecs
     }
 
-    internal fun addSimulcastTrack(codec: VideoCodec, encodings: List<RtpParameters.Encoding>): SimulcastTrackInfo {
+    internal fun addSimulcastTrack(codec: VideoCodec, encodings: List<RtpParameters.Encoding>): SimulcastTrackInfo? {
         if (this.simulcastCodecs.containsKey(codec)) {
-            throw IllegalStateException("$codec already added!")
+            LKLog.w { "$codec already added, skipping." }
+            return null
         }
         val simulcastTrackInfo = SimulcastTrackInfo(
             codec = codec.codecName,
diff --git a/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt b/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
index 0498b8ed1..43869ea83 100644
--- a/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
+++ b/livekit-android-test/src/test/java/io/livekit/android/room/participant/LocalParticipantMockE2ETest.kt
@@ -340,6 +340,36 @@ class LocalParticipantMockE2ETest : MockE2ETest() {
         assertEquals(4, getPublisherPeerConnection().transceivers.size)
     }
 
+    @Test
+    fun addSimulcastTrackForAlreadyAddedCodecIsNoOp() = runTest {
+        val videoTrack = createLocalTrack()
+
+        val first = videoTrack.addSimulcastTrack(VideoCodec.VP8, emptyList())
+        val second = videoTrack.addSimulcastTrack(VideoCodec.VP8, emptyList())
+
+        assertNotNull(first)
+        assertNull(second)
+    }
+
+    @Test
+    fun duplicateSubscribedQualityUpdateDoesNotRepublishBackupCodec() = runTest {
+        room.videoTrackPublishDefaults = room.videoTrackPublishDefaults.copy(
+            videoCodec = VideoCodec.VP9.codecName,
+            scalabilityMode = "L3T3",
+            backupCodec = BackupVideoCodec(codec = VideoCodec.VP8.codecName),
+        )
+
+        connect()
+        val videoTrack = createLocalTrack()
+        room.localParticipant.publishVideoTrack(videoTrack)
+
+        val trackSid = room.localParticipant.videoTrackPublications.first().first.sid
+        receiveSubscribedQualityUpdate(trackSid)
+        receiveSubscribedQualityUpdate(trackSid)
+
+        assertEquals(2, getPublisherPeerConnection().transceivers.size)
+    }
+
     @Test
     fun disposeDisposesVideoSource() {
         val source = mock(VideoSource::class.java)