major refactor, simplified TrackPublication hierarchy

@@ -153,9 +153,9 @@ constructor(
         sendRequest(request)
     }
 
-    fun sendMuteTrack(trackSid: Track.Sid, muted: Boolean) {
+    fun sendMuteTrack(trackSid: String, muted: Boolean) {
         val muteRequest = LivekitRtc.MuteTrackRequest.newBuilder()
-            .setSid(trackSid.sid)
+            .setSid(trackSid)
             .setMuted(muted)
             .build()
 
@@ -166,9 +166,9 @@ constructor(
         sendRequest(request)
     }
 
-    fun sendAddTrack(cid: Track.Cid, name: String, type: LivekitModels.TrackType) {
+    fun sendAddTrack(cid: String, name: String, type: LivekitModels.TrackType) {
         val addTrackRequest = LivekitRtc.AddTrackRequest.newBuilder()
-            .setCid(cid.cid)
+            .setCid(cid)
             .setName(name)
             .setType(type)
             .build()

@@ -45,7 +45,7 @@ constructor(
             }
         }
     val pendingCandidates = mutableListOf<IceCandidate>()
-    private val pendingTrackResolvers: MutableMap<Track.Cid, Continuation<LivekitModels.TrackInfo>> =
+    private val pendingTrackResolvers: MutableMap<String, Continuation<LivekitModels.TrackInfo>> =
         mutableMapOf()
 
     private val publisherObserver = PublisherTransportObserver(this)
@@ -76,7 +76,7 @@ constructor(
         client.join(url, token)
     }
 
-    suspend fun addTrack(cid: Track.Cid, name: String, kind: LivekitModels.TrackType): LivekitModels.TrackInfo {
+    suspend fun addTrack(cid: String, name: String, kind: LivekitModels.TrackType): LivekitModels.TrackInfo {
         if (pendingTrackResolvers[cid] != null) {
             throw TrackException.DuplicateTrackException("Track with same ID $cid has already been published!")
         }
@@ -87,7 +87,7 @@ constructor(
         }
     }
 
-    fun updateMuteStatus(sid: Track.Sid, muted: Boolean) {
+    fun updateMuteStatus(sid: String, muted: Boolean) {
         client.sendMuteTrack(sid, muted)
     }
 
@@ -137,7 +137,7 @@ constructor(
     interface Listener {
         fun onJoin(response: LivekitRtc.JoinResponse)
         fun onAddTrack(track: MediaStreamTrack, streams: Array<out MediaStream>)
-        fun onPublishLocalTrack(cid: Track.Cid, track: LivekitModels.TrackInfo)
+        fun onPublishLocalTrack(cid: String, track: LivekitModels.TrackInfo)
         fun onAddDataChannel(channel: DataChannel)
         fun onUpdateParticipants(updates: List<LivekitModels.ParticipantInfo>)
         fun onUpdateSpeakers(speakers: List<LivekitRtc.SpeakerInfo>)
@@ -253,7 +253,7 @@ constructor(
             Timber.e { "local track published with null cid?" }
             return
         }
-        val cid = Track.Cid(signalCid)
+        val cid = signalCid
 
         val track = response.track
         if (track == null) {

@@ -9,7 +9,6 @@ import io.livekit.android.ConnectOptions
 import io.livekit.android.room.participant.LocalParticipant
 import io.livekit.android.room.participant.Participant
 import io.livekit.android.room.participant.RemoteParticipant
-import io.livekit.android.room.track.Track
 import io.livekit.android.room.util.unpackedTrackLabel
 import livekit.LivekitModels
 import livekit.LivekitRtc
@@ -24,7 +23,7 @@ constructor(
     @Assisted private val connectOptions: ConnectOptions,
     private val engine: RTCEngine,
     private val eglBase: EglBase,
-) : RTCEngine.Listener, RemoteParticipant.Listener, LocalParticipant.Listener {
+) : RTCEngine.Listener, RemoteParticipant.Listener {
     init {
         engine.listener = this
     }
@@ -48,8 +47,8 @@ constructor(
         private set
     var localParticipant: LocalParticipant? = null
         private set
-    private val mutableRemoteParticipants = mutableMapOf<Participant.Sid, RemoteParticipant>()
-    val remoteParticipants: Map<Participant.Sid, RemoteParticipant>
+    private val mutableRemoteParticipants = mutableMapOf<String, RemoteParticipant>()
+    val remoteParticipants: Map<String, RemoteParticipant>
         get() = mutableRemoteParticipants
 
     private val mutableActiveSpeakers = mutableListOf<Participant>()
@@ -73,17 +72,17 @@ constructor(
         listener?.onDisconnect(this, null)
     }
 
-    private fun handleParticipantDisconnect(sid: Participant.Sid, participant: RemoteParticipant) {
+    private fun handleParticipantDisconnect(sid: String, participant: RemoteParticipant) {
         val removedParticipant = mutableRemoteParticipants.remove(sid) ?: return
         removedParticipant.tracks.values.forEach { publication ->
-            removedParticipant.unpublishTrack(publication.trackSid)
+            removedParticipant.unpublishTrack(publication.sid)
         }
 
         listener?.onParticipantDisconnected(this, removedParticipant)
     }
 
     private fun getOrCreateRemoteParticipant(
-        sid: Participant.Sid,
+        sid: String,
         info: LivekitModels.ParticipantInfo? = null
     ): RemoteParticipant {
         var participant = remoteParticipants[sid]
@@ -103,10 +102,10 @@ constructor(
 
     private fun handleSpeakerUpdate(speakerInfos: List<LivekitRtc.SpeakerInfo>) {
         val speakers = mutableListOf<Participant>()
-        val seenSids = mutableSetOf<Participant.Sid>()
+        val seenSids = mutableSetOf<String>()
         val localParticipant = localParticipant
         speakerInfos.forEach { speakerInfo ->
-            val speakerSid = Participant.Sid(speakerInfo.sid)
+            val speakerSid = speakerInfo.sid!!
             seenSids.add(speakerSid)
 
             if (speakerSid == localParticipant?.sid) {
@@ -185,7 +184,7 @@ constructor(
         }
         if (response.otherParticipantsList.isNotEmpty()) {
             response.otherParticipantsList.forEach {
-                getOrCreateRemoteParticipant(Participant.Sid(it.sid), it)
+                getOrCreateRemoteParticipant(it.sid, it)
             }
         }
 
@@ -203,8 +202,8 @@ constructor(
             return
         }
 
-        val participantSid = Participant.Sid(streams.first().id)
-        val trackSid = Track.Sid(track.id())
+        val participantSid = streams.first().id
+        val trackSid = track.id()
         val participant = getOrCreateRemoteParticipant(participantSid)
         participant.addSubscribedMediaTrack(track, trackSid)
     }
@@ -222,7 +221,7 @@ constructor(
     /**
      * @suppress
      */
-    override fun onPublishLocalTrack(cid: Track.Cid, track: LivekitModels.TrackInfo) {
+    override fun onPublishLocalTrack(cid: String, track: LivekitModels.TrackInfo) {
     }
 
     /**
@@ -230,7 +229,7 @@ constructor(
      */
     override fun onUpdateParticipants(updates: List<LivekitModels.ParticipantInfo>) {
         for (info in updates) {
-            val participantSid = Participant.Sid(info.sid)
+            val participantSid = info.sid
 
             if(localParticipant?.sid == participantSid) {
                 localParticipant?.updateFromInfo(info)

@@ -8,28 +8,16 @@ import org.webrtc.DataChannel
 import org.webrtc.RtpTransceiver
 import java.util.*
 
-class LocalParticipant(sid: Sid, name: String? = null) :
-    Participant(sid, name) {
-
-    /**
-     * @suppress
-     */
-    constructor(info: LivekitModels.ParticipantInfo, engine: RTCEngine) : this(
-        Sid(info.sid),
-        info.identity
-    ) {
-        metadata = info.metadata
-        this.engine = engine
+class LocalParticipant(info: LivekitModels.ParticipantInfo, private val engine: RTCEngine) :
+    Participant(info.sid, info.identity) {
+
+    init {
+        updateFromInfo(info)
     }
 
-    val localAudioTrackPublications
-        get() = audioTracks.values.toList()
-    val localVideoTrackPublications
-        get() = videoTracks.values.toList()
-    val localDataTrackPublications
-        get() = dataTracks.values.toList()
+    val localTrackPublications
+        get() = tracks.values.toList()
 
-    private var engine: RTCEngine? = null
     var listener: Listener? = null
         set(v) {
             field = v
@@ -38,98 +26,77 @@ class LocalParticipant(sid: Sid, name: String? = null) :
 
     suspend fun publishAudioTrack(
         track: LocalAudioTrack,
-        options: LocalTrackPublicationOptions? = null
+        publishListener: PublishListener? = null
     ) {
-        if (localAudioTrackPublications.any { it.track == track }) {
-            listener?.onFailToPublishAudioTrack(TrackException.PublishException("Track has already been published"))
+        if (localTrackPublications.any { it.track == track }) {
+            publishListener?.onPublishFailure(TrackException.PublishException("Track has already been published"))
             return
         }
 
         val cid = track.rtcTrack.id()
-        val engine = this.engine ?: run {
-            listener?.onFailToPublishAudioTrack(IllegalStateException("engine is null!"))
-            return
-        }
-
         val trackInfo =
-            engine.addTrack(cid = Track.Cid(cid), name = track.name, kind = LivekitModels.TrackType.AUDIO)
+            engine.addTrack(cid = cid, name = track.name, kind = track.kind)
         val transInit = RtpTransceiver.RtpTransceiverInit(
             RtpTransceiver.RtpTransceiverDirection.SEND_ONLY,
-            listOf(this.sid.sid)
+            listOf(this.sid)
         )
+        // TODO: sendEncodings to customize
         val transceiver =
             engine.publisher.peerConnection.addTransceiver(track.rtcTrack, transInit)
 
         if (transceiver == null) {
-            listener?.onFailToPublishAudioTrack(TrackException.PublishException("null sender returned from peer connection"))
+            publishListener?.onPublishFailure(TrackException.PublishException("null sender returned from peer connection"))
             return
         }
 
-        val publication = LocalAudioTrackPublication(trackInfo)
-        val trackSid = Track.Sid(trackInfo.sid)
-        track.sid = trackSid
-        audioTracks[trackSid] = publication
-        listener?.onPublishAudioTrack(track)
+        val publication = TrackPublication(trackInfo, track)
+        addTrackPublication(publication)
+        publishListener?.onPublishSuccess(publication)
     }
 
     suspend fun publishVideoTrack(
         track: LocalVideoTrack,
-        options: LocalTrackPublicationOptions? = null
+        publishListener: PublishListener? = null
     ) {
-
-        if (localVideoTrackPublications.any { it.track == track }) {
-            listener?.onFailToPublishVideoTrack(TrackException.PublishException("Track has already been published"))
+        if (localTrackPublications.any { it.track == track }) {
+            publishListener?.onPublishFailure(TrackException.PublishException("Track has already been published"))
             return
         }
 
         val cid = track.rtcTrack.id()
-        val engine = this.engine ?: run {
-            listener?.onFailToPublishVideoTrack(IllegalStateException("engine is null!"))
-            return
-        }
-
         val trackInfo =
-            engine.addTrack(cid = Track.Cid(cid), name = track.name, kind = LivekitModels.TrackType.VIDEO)
+            engine.addTrack(cid = cid, name = track.name, kind = LivekitModels.TrackType.VIDEO)
         val transInit = RtpTransceiver.RtpTransceiverInit(
             RtpTransceiver.RtpTransceiverDirection.SEND_ONLY,
-            listOf(this.sid.sid)
+            listOf(this.sid)
         )
+        // TODO: video encodings & simulcast
         val transceiver =
             engine.publisher.peerConnection.addTransceiver(track.rtcTrack, transInit)
 
         if (transceiver == null) {
-            listener?.onFailToPublishVideoTrack(TrackException.PublishException("null sender returned from peer connection"))
+            publishListener?.onPublishFailure(TrackException.PublishException("null sender returned from peer connection"))
             return
         }
 
-        val publication = LocalVideoTrackPublication(trackInfo)
-        val trackSid = Track.Sid(trackInfo.sid)
-        track.sid = trackSid
-        videoTracks[trackSid] = publication
-        listener?.onPublishVideoTrack(track)
+        val publication = TrackPublication(trackInfo, track)
+        addTrackPublication(publication)
+        publishListener?.onPublishSuccess(publication)
     }
 
     suspend fun publishDataTrack(
         track: LocalDataTrack,
-        options: LocalTrackPublicationOptions? = null
+        publishListener: PublishListener? = null
     ) {
-
-        if (localDataTrackPublications.any { it.track == track }) {
-            listener?.onFailToPublishDataTrack(TrackException.PublishException("Track has already been published"))
+        if (localTrackPublications.any { it.track == track }) {
+            publishListener?.onPublishFailure(TrackException.PublishException("Track has already been published"))
             return
         }
 
         val cid = track.cid
-        val engine = this.engine ?: run {
-            listener?.onFailToPublishDataTrack(IllegalStateException("engine is null!"))
-            return
-        }
-
         val trackInfo =
-            engine.addTrack(cid = cid, name = track.name, kind = LivekitModels.TrackType.DATA)
-        val publication = LocalDataTrackPublication(trackInfo, track)
-        val trackSid = Track.Sid(trackInfo.sid)
-        track.sid = trackSid
+            engine.addTrack(cid = cid, name = track.name, track.kind)
+        val publication = TrackPublication(trackInfo, track)
 
         val config = DataChannel.Init().apply {
             ordered = track.options.ordered
@@ -138,76 +105,51 @@ class LocalParticipant(sid: Sid, name: String? = null) :
         }
 
         val dataChannel = engine.publisher.peerConnection.createDataChannel(track.name, config)
-        if (dataChannel != null) {
-            track.rtcTrack = dataChannel
-            track.updateConfig(config)
-            dataTracks[trackSid] = publication
-            listener?.onPublishDataTrack(track)
-        } else {
-            Timber.d { "error creating data channel with name: $name" }
-            unpublishDataTrack(track)
-        }
-    }
-
-    fun unpublishAudioTrack(track: LocalAudioTrack) {
-        val sid = track.sid ?: run {
-            Timber.d { "this track was never published." }
+        if (dataChannel == null) {
+            publishListener?.onPublishFailure(TrackException.PublishException("could not create data channel"))
             return
         }
-        unpublishMediaTrack(track, sid, audioTracks)
-    }
+        track.dataChannel = dataChannel
+        track.updateConfig(config)
+        addTrackPublication(publication)
 
-    fun unpublishVideoTrack(track: LocalVideoTrack) {
-        val sid = track.sid ?: run {
-            Timber.d { "this track was never published." }
-            return
-        }
-        unpublishMediaTrack(track, sid, audioTracks)
+        publishListener?.onPublishSuccess(publication)
     }
 
-    fun unpublishDataTrack(track: LocalDataTrack) {
-        val sid = track.sid ?: run {
+    fun unpublishTrack(track: Track) {
+        val publication = localTrackPublications.firstOrNull { it.track == track }
+        if (publication === null) {
             Timber.d { "this track was never published." }
             return
         }
-
-        val publication = dataTracks.remove(sid) as? LocalDataTrackPublication
-        if (publication == null) {
-            Timber.d { "track was not published with sid: $sid" }
-            return
+        track.stop()
+        if (track is MediaTrack) {
+            unpublishMediaTrack(track, sid)
+        }
+        val sid = publication.sid
+        tracks.remove(sid)
+        when (publication.kind) {
+            LivekitModels.TrackType.AUDIO -> audioTracks.remove(sid)
+            LivekitModels.TrackType.VIDEO -> videoTracks.remove(sid)
+            LivekitModels.TrackType.DATA -> dataTracks.remove(sid)
         }
-        publication.dataTrack?.rtcTrack?.dispose()
     }
 
     private fun <T> unpublishMediaTrack(
         track: T,
-        sid: Track.Sid,
-        publications: MutableMap<Track.Sid, TrackPublication>
-    ) where T : Track, T : MediaTrack {
-        val removed = publications.remove(sid)
-        if (removed != null) {
-            Timber.d { "track was not published with sid: $sid" }
-            return
-        }
-
-        track.mediaTrack.setEnabled(false)
+        sid: String
+    ) where T : MediaTrack {
         val senders = engine?.publisher?.peerConnection?.senders ?: return
         for (sender in senders) {
             val t = sender.track() ?: continue
-            if (t == track.mediaTrack) {
+            if (t == track.rtcTrack) {
                 engine?.publisher?.peerConnection?.removeTrack(sender)
             }
         }
     }
 
-    interface Listener : Participant.Listener {
-        // TODO: can we move these to exceptions? instead of callbacks
-        fun onPublishAudioTrack(track: LocalAudioTrack) {}
-        fun onFailToPublishAudioTrack(exception: Exception) {}
-        fun onPublishVideoTrack(track: LocalVideoTrack) {}
-        fun onFailToPublishVideoTrack(exception: Exception) {}
-        fun onPublishDataTrack(track: LocalDataTrack) {}
-        fun onFailToPublishDataTrack(exception: Exception) {}
-        //fun onNetworkQualityLevelChange
+    interface PublishListener {
+        fun onPublishSuccess(publication: TrackPublication) {}
+        fun onPublishFailure(exception: Exception) {}
     }
 }

@@ -3,12 +3,10 @@ package io.livekit.android.room.participant
 import io.livekit.android.room.track.*
 import livekit.LivekitModels
 
-open class Participant(var sid: Sid, name: String? = null) {
-    inline class Sid(val sid: String)
-
+open class Participant(var sid: String, identity: String? = null) {
     var participantInfo: LivekitModels.ParticipantInfo? = null
         private set
-    var name: String? = name
+    var identity: String? = identity
         internal set
     var audioLevel: Float = 0f
         internal set
@@ -17,23 +15,23 @@ open class Participant(var sid: Sid, name: String? = null) {
     val hasInfo
         get() = participantInfo != null
 
-    var tracks = mutableMapOf<Track.Sid, TrackPublication>()
-    var audioTracks = mutableMapOf<Track.Sid, TrackPublication>()
+    var tracks = mutableMapOf<String, TrackPublication>()
+    var audioTracks = mutableMapOf<String, TrackPublication>()
         private set
-    var videoTracks = mutableMapOf<Track.Sid, TrackPublication>()
+    var videoTracks = mutableMapOf<String, TrackPublication>()
         private set
-    var dataTracks = mutableMapOf<Track.Sid, TrackPublication>()
+    var dataTracks = mutableMapOf<String, TrackPublication>()
         private set
 
     /**
      * @suppress
      */
-    fun addTrack(publication: TrackPublication) {
-        tracks[publication.trackSid] = publication
-        when (publication) {
-            is RemoteAudioTrackPublication -> audioTracks[publication.trackSid] = publication
-            is RemoteVideoTrackPublication -> videoTracks[publication.trackSid] = publication
-            is RemoteDataTrackPublication -> dataTracks[publication.trackSid] = publication
+    fun addTrackPublication(publication: TrackPublication) {
+        tracks[publication.sid] = publication
+        when (publication.kind) {
+            LivekitModels.TrackType.AUDIO -> audioTracks[publication.sid] = publication
+            LivekitModels.TrackType.VIDEO -> videoTracks[publication.sid] = publication
+            LivekitModels.TrackType.DATA -> dataTracks[publication.sid] = publication
         }
     }
 
@@ -41,8 +39,8 @@ open class Participant(var sid: Sid, name: String? = null) {
      * @suppress
      */
     open fun updateFromInfo(info: LivekitModels.ParticipantInfo) {
-        sid = Sid(info.sid)
-        name = info.identity
+        sid = info.sid
+        identity = info.identity
         participantInfo = info
 
         val prevMetadata = metadata

@@ -14,22 +14,15 @@ import org.webrtc.VideoTrack
 import java.nio.ByteBuffer
 
 class RemoteParticipant(
-    sid: Sid, name: String? = null
+    sid: String, name: String? = null
 ) : Participant(sid, name), RemoteDataTrack.Listener {
     /**
      * @suppress
      */
-    constructor(info: LivekitModels.ParticipantInfo) : this(Sid(info.sid), info.identity) {
+    constructor(info: LivekitModels.ParticipantInfo) : this(info.sid, info.identity) {
         updateFromInfo(info)
     }
 
-    val remoteAudioTracks
-        get() = audioTracks.values.toList()
-    val remoteVideoTracks
-        get() = videoTracks.values.toList()
-    val remoteDataTracks
-        get() = dataTracks.values.toList()
-
     var listener: Listener? = null
         set(v) {
             field = v
@@ -38,8 +31,8 @@ class RemoteParticipant(
 
     private val coroutineScope = CloseableCoroutineScope(SupervisorJob())
 
-    fun getTrackPublication(sid: Track.Sid): RemoteTrackPublication? =
-        tracks[sid] as? RemoteTrackPublication
+    fun getTrackPublication(sid: String): TrackPublication? =
+        tracks[sid]
 
     /**
      * @suppress
@@ -48,24 +41,18 @@ class RemoteParticipant(
         val hadInfo = hasInfo
         super.updateFromInfo(info)
 
-        val validTrackPublication = mutableMapOf<Track.Sid, RemoteTrackPublication>()
-        val newTrackPublications = mutableMapOf<Track.Sid, RemoteTrackPublication>()
+        val validTrackPublication = mutableMapOf<String, TrackPublication>()
+        val newTrackPublications = mutableMapOf<String, TrackPublication>()
 
         for (trackInfo in info.tracksList) {
-            val trackSid = Track.Sid(trackInfo.sid)
+            val trackSid = trackInfo.sid
             var publication = getTrackPublication(trackSid)
 
             if (publication == null) {
-                publication = when (trackInfo.type) {
-                    LivekitModels.TrackType.AUDIO -> RemoteAudioTrackPublication(trackInfo)
-                    LivekitModels.TrackType.VIDEO -> RemoteVideoTrackPublication(trackInfo)
-                    LivekitModels.TrackType.DATA -> RemoteDataTrackPublication(trackInfo)
-                    LivekitModels.TrackType.UNRECOGNIZED -> throw TrackException.InvalidTrackTypeException()
-                    null -> throw NullPointerException("trackInfo.type is null")
-                }
+                publication = TrackPublication(trackInfo)
 
                 newTrackPublications[trackSid] = publication
-                addTrack(publication)
+                addTrackPublication(publication)
             } else {
                 publication.updateFromInfo(trackInfo)
             }
@@ -75,25 +62,25 @@ class RemoteParticipant(
 
         if (hadInfo) {
             for (publication in newTrackPublications.values) {
-                sendTrackPublishedEvent(publication)
+                listener?.onPublish(publication, this)
             }
         }
 
         val invalidKeys = tracks.keys - validTrackPublication.keys
         for (invalidKey in invalidKeys) {
             val publication = tracks[invalidKey] ?: continue
-            unpublishTrack(publication.trackSid, true)
+            unpublishTrack(publication.sid, true)
         }
     }
 
     /**
      * @suppress
      */
-    fun addSubscribedMediaTrack(rtcTrack: MediaStreamTrack, sid: Track.Sid, triesLeft: Int = 20) {
+    fun addSubscribedMediaTrack(mediaTrack: MediaStreamTrack, sid: String, triesLeft: Int = 20) {
         val publication = getTrackPublication(sid)
-        val track: Track = when (val kind = rtcTrack.kind()) {
-            KIND_AUDIO -> RemoteAudioTrack(sid = sid, rtcTrack = rtcTrack as AudioTrack, name = "")
-            KIND_VIDEO -> RemoteVideoTrack(sid = sid, rtcTrack = rtcTrack as VideoTrack, name = "")
+        val track: Track = when (val kind = mediaTrack.kind()) {
+            KIND_AUDIO -> RemoteAudioTrack(sid = sid, mediaTrack = mediaTrack as AudioTrack, name = "")
+            KIND_VIDEO -> RemoteVideoTrack(sid = sid, mediaTrack = mediaTrack as VideoTrack, name = "")
             else -> throw TrackException.InvalidTrackTypeException("invalid track type: $kind")
         }
 
@@ -102,27 +89,12 @@ class RemoteParticipant(
                 val message = "Could not find published track with sid: $sid"
                 val exception = TrackException.InvalidTrackStateException(message)
                 Timber.e { "remote participant ${this.sid} --- $message" }
-                when (rtcTrack.kind()) {
-                    KIND_AUDIO -> {
-                        listener?.onFailToSubscribe(
-                            audioTrack = track as RemoteAudioTrack,
-                            exception = exception,
-                            participant = this
-                        )
-                    }
-
-                    KIND_VIDEO -> {
-                        listener?.onFailToSubscribe(
-                            videoTrack = track as RemoteVideoTrack,
-                            exception = exception,
-                            participant = this
-                        )
-                    }
-                }
+
+                listener?.onFailToSubscribe(sid, exception, this)
             } else {
                 coroutineScope.launch {
                     delay(150)
-                    addSubscribedMediaTrack(rtcTrack, sid, triesLeft - 1)
+                    addSubscribedMediaTrack(mediaTrack, sid, triesLeft - 1)
                 }
             }
             return
@@ -130,103 +102,70 @@ class RemoteParticipant(
 
         val remoteTrack = track as RemoteTrack
         publication.track = track
-        track.name = publication.trackName
-        remoteTrack.sid = publication.trackSid
+        track.name = publication.name
+        remoteTrack.sid = publication.sid
 
-        when (publication) {
-            is RemoteAudioTrackPublication -> listener?.onSubscribe(publication, this)
-            is RemoteVideoTrackPublication -> listener?.onSubscribe(publication, this)
-            else -> throw TrackException.InvalidTrackTypeException()
-        }
+        // TODO: how does mediatrack send ended event?
+
+        listener?.onSubscribe(track, publication, this)
     }
 
     /**
      * @suppress
      */
-    fun addSubscribedDataTrack(rtcTrack: DataChannel, sid: Track.Sid, name: String) {
-        val track = RemoteDataTrack(sid, name, rtcTrack)
-        var publication = getTrackPublication(sid) as? RemoteDataTrackPublication
+    fun addSubscribedDataTrack(dataChannel: DataChannel, sid: String, name: String) {
+        val track = DataTrack(name, dataChannel)
+        var publication = getTrackPublication(sid)
 
         if (publication != null) {
             publication.track = track
         } else {
             val trackInfo = LivekitModels.TrackInfo.newBuilder()
-                .setSid(sid.sid)
+                .setSid(sid)
                 .setName(name)
                 .setType(LivekitModels.TrackType.DATA)
                 .build()
-            publication = RemoteDataTrackPublication(info = trackInfo, track = track)
-            addTrack(publication)
+            publication = TrackPublication(info = trackInfo, track = track)
+            addTrackPublication(publication)
             if (hasInfo) {
-                sendTrackPublishedEvent(publication)
+                listener?.onPublish(publication, this)
             }
         }
 
-
-        rtcTrack.registerObserver(object : DataChannel.Observer {
+        dataChannel.registerObserver(object : DataChannel.Observer {
             override fun onBufferedAmountChange(previousAmount: Long) {}
 
             override fun onStateChange() {
-                val newState = rtcTrack.state()
+                val newState = dataChannel.state()
                 if (newState == DataChannel.State.CLOSED) {
-                    listener?.onUnsubscribe(publication, this@RemoteParticipant)
+                    publication.track = null
+                    listener?.onUnsubscribe(track, publication, this@RemoteParticipant)
                 }
             }
 
             override fun onMessage(buffer: DataChannel.Buffer) {
-                listener?.onReceive(buffer.data, publication, this@RemoteParticipant)
+                listener?.onReceive(buffer.data, track, this@RemoteParticipant)
             }
         })
-        listener?.onSubscribe(dataTrack = publication, participant = this)
+        listener?.onSubscribe(track, publication, participant = this)
     }
 
-    fun unpublishTrack(trackSid: Track.Sid, sendUnpublish: Boolean = false) {
+    fun unpublishTrack(trackSid: String, sendUnpublish: Boolean = false) {
         val publication = tracks.remove(trackSid) ?: return
-
-        when (publication) {
-            is RemoteAudioTrackPublication -> audioTracks.remove(trackSid)
-            is RemoteVideoTrackPublication -> videoTracks.remove(trackSid)
-            is RemoteDataTrackPublication -> {
-                dataTracks.remove(trackSid)
-                publication.dataTrack?.rtcTrack?.unregisterObserver()
-            }
+        when (publication.kind) {
+            LivekitModels.TrackType.AUDIO -> audioTracks.remove(trackSid)
+            LivekitModels.TrackType.VIDEO -> videoTracks.remove(trackSid)
+            LivekitModels.TrackType.DATA -> dataTracks.remove(trackSid)
             else -> throw TrackException.InvalidTrackTypeException()
         }
 
-        if (publication.track != null) {
-            // TODO: need to stop track?
-            publication.track
-            sendTrackUnsubscribedEvent(publication)
+        val track = publication.track
+        if (track != null) {
+            track.stop()
+            listener?.onUnsubscribe(track, publication, this)
         }
         if (sendUnpublish) {
-            sendTrackUnpublishedEvent(publication)
-        }
-    }
-
-    private fun sendTrackUnsubscribedEvent(publication: TrackPublication) {
-        when (publication) {
-            is RemoteAudioTrackPublication -> listener?.onUnsubscribe(publication, this)
-            is RemoteVideoTrackPublication -> listener?.onUnsubscribe(publication, this)
-            is RemoteDataTrackPublication -> listener?.onUnsubscribe(publication, this)
-            else -> throw TrackException.InvalidTrackTypeException()
-        }
-    }
-
-    private fun sendTrackUnpublishedEvent(publication: TrackPublication) {
-        when (publication) {
-            is RemoteAudioTrackPublication -> listener?.onUnpublish(publication, this)
-            is RemoteVideoTrackPublication -> listener?.onUnpublish(publication, this)
-            is RemoteDataTrackPublication -> listener?.onUnpublish(publication, this)
-            else -> throw TrackException.InvalidTrackTypeException()
-        }
-    }
-
-    private fun sendTrackPublishedEvent(publication: RemoteTrackPublication) {
-        when (publication) {
-            is RemoteAudioTrackPublication -> listener?.onPublish(publication, this)
-            is RemoteVideoTrackPublication -> listener?.onPublish(publication, this)
-            is RemoteDataTrackPublication -> listener?.onPublish(publication, this)
-            else -> throw TrackException.InvalidTrackTypeException()
+            listener?.onUnpublish(publication, this)
         }
     }
 
@@ -244,68 +183,36 @@ class RemoteParticipant(
     }
 
     interface Listener: Participant.Listener {
-        fun onPublish(audioTrack: RemoteAudioTrackPublication, participant: RemoteParticipant) {}
-        fun onUnpublish(audioTrack: RemoteAudioTrackPublication, participant: RemoteParticipant) {}
-        fun onPublish(videoTrack: RemoteVideoTrackPublication, participant: RemoteParticipant) {}
-        fun onUnpublish(videoTrack: RemoteVideoTrackPublication, participant: RemoteParticipant) {}
-        fun onPublish(dataTrack: RemoteDataTrackPublication, participant: RemoteParticipant) {}
-        fun onUnpublish(dataTrack: RemoteDataTrackPublication, participant: RemoteParticipant) {}
-
-        fun onEnable(audioTrack: RemoteAudioTrackPublication, participant: RemoteParticipant) {}
-        fun onDisable(audioTrack: RemoteAudioTrackPublication, participant: RemoteParticipant) {}
-        fun onEnable(videoTrack: RemoteVideoTrackPublication, participant: RemoteParticipant) {}
-        fun onDisable(videoTrack: RemoteVideoTrackPublication, participant: RemoteParticipant) {}
-
-        fun onSubscribe(audioTrack: RemoteAudioTrackPublication, participant: RemoteParticipant) {}
-        fun onFailToSubscribe(
-            audioTrack: RemoteAudioTrack,
-            exception: Exception,
-            participant: RemoteParticipant
-        ) {
-        }
+        fun onPublish(publication: TrackPublication, participant: RemoteParticipant) {}
+        fun onUnpublish(publication: TrackPublication, participant: RemoteParticipant) {}
 
-        fun onUnsubscribe(
-            audioTrack: RemoteAudioTrackPublication,
-            participant: RemoteParticipant
-        ) {
-        }
+        fun onEnable(publication: TrackPublication, participant: RemoteParticipant) {}
+        fun onDisable(publication: TrackPublication, participant: RemoteParticipant) {}
 
-        fun onSubscribe(videoTrack: RemoteVideoTrackPublication, participant: RemoteParticipant) {}
+        fun onSubscribe(track: Track, publication: TrackPublication, participant: RemoteParticipant) {}
         fun onFailToSubscribe(
-            videoTrack: RemoteVideoTrack,
+            sid: String,
             exception: Exception,
             participant: RemoteParticipant
         ) {
         }
 
         fun onUnsubscribe(
-            videoTrack: RemoteVideoTrackPublication,
-            participant: RemoteParticipant
-        ) {
-        }
-
-        fun onSubscribe(dataTrack: RemoteDataTrackPublication, participant: RemoteParticipant) {}
-        fun onFailToSubscribe(
-            dataTrack: RemoteDataTrackPublication,
-            exception: Exception,
+            track: Track,
+            publications: TrackPublication,
             participant: RemoteParticipant
         ) {
         }
 
-        fun onUnsubscribe(dataTrack: RemoteDataTrackPublication, participant: RemoteParticipant) {}
         fun onReceive(
             data: ByteBuffer,
-            dataTrack: RemoteDataTrackPublication,
+            dataTrack: DataTrack,
             participant: RemoteParticipant
         ) {
         }
 
-        //fun networkQualityDidChange(networkQualityLevel: NetworkQualityLevel, participant: remoteParticipant)
         fun switchedOffVideo(track: RemoteVideoTrack, participant: RemoteParticipant) {}
         fun switchedOnVideo(track: RemoteVideoTrack, participant: RemoteParticipant) {}
-//        fun onChangePublishPriority(videoTrack: RemoteVideoTrackPublication, priority: PublishPriority, participant: RemoteParticipant)
-//        fun onChangePublishPriority(audioTrack: RemoteAudioTrackPublication, priority: PublishPriority, participant: RemoteParticipant)
-//        fun onChangePublishPriority(dataTrack: RemoteDataTrackPublication, priority: PublishPriority, participant: RemoteParticipant)
     }
 
 }
\ No newline at end of file

 package io.livekit.android.room.track
 
+import livekit.LivekitModels
 import org.webrtc.AudioTrack
-import org.webrtc.MediaStreamTrack
 
-open class AudioTrack(name: String, val rtcTrack: AudioTrack) :
-    Track(name, stateFromRTCMediaTrackState(rtcTrack.state())),
-    MediaTrack {
+open class AudioTrack(name: String, override val rtcTrack: AudioTrack) :
+    MediaTrack(name, LivekitModels.TrackType.AUDIO, rtcTrack) {
 
-    override val mediaTrack: MediaStreamTrack
-        get() = rtcTrack
 }
\ No newline at end of file

-package io.livekit.android.room.track
-
-interface AudioTrackPublication {
-    val audioTrack: AudioTrack?
-}
\ No newline at end of file

 package io.livekit.android.room.track
 
+import livekit.LivekitModels
 import org.webrtc.DataChannel
 
 open class DataTrack(
     name: String,
-    var rtcTrack: DataChannel? = null
-) : Track(
-    name,
-    run {
-        if (rtcTrack != null) {
-            stateFromRTCDataChannelState(rtcTrack.state())
-        } else {
-            State.NONE
-        }
-    }) {
-
+    var dataChannel: DataChannel? = null
+) : Track(name, LivekitModels.TrackType.DATA) {
     var ordered: Boolean = TODO()
         private set
     var maxRetransmitTimeMs: Int = TODO()
@@ -27,4 +19,8 @@ open class DataTrack(
         maxRetransmitTimeMs = config.maxRetransmitTimeMs
         maxRetransmits = config.maxRetransmits
     }
-}
\ No newline at end of file
+
+    override fun stop() {
+        dataChannel?.unregisterObserver()
+    }
+}

-package io.livekit.android.room.track
-
-interface DataTrackPublication {
-    val dataTrack: DataTrack?
-}
\ No newline at end of file

@@ -7,16 +7,14 @@ import java.util.*
 class LocalAudioTrack(
     name: String,
     audioOptions: AudioOptions? = null,
-    rtcTrack: org.webrtc.AudioTrack
-) : AudioTrack(name, rtcTrack) {
+    mediaTrack: org.webrtc.AudioTrack
+) : AudioTrack(name, mediaTrack) {
     var enabled: Boolean
         get() = rtcTrack.enabled()
         set(value) {
             rtcTrack.setEnabled(value)
         }
 
-    var sid: Sid? = null
-        internal set
     var audioOptions = audioOptions
         private set
 
@@ -31,7 +29,7 @@ class LocalAudioTrack(
             val rtcAudioTrack =
                 factory.createAudioTrack(UUID.randomUUID().toString(), audioSource)
 
-            return LocalAudioTrack(name = name, rtcTrack = rtcAudioTrack)
+            return LocalAudioTrack(name = name, mediaTrack = rtcAudioTrack)
         }
     }
-}
\ No newline at end of file
+}

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class LocalAudioTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    LocalTrackPublication(info, track), AudioTrackPublication {
-    override val audioTrack: AudioTrack?
-        get() = track as? AudioTrack
-}

@@ -5,21 +5,20 @@ import java.nio.ByteBuffer
 import java.util.*
 
 class LocalDataTrack(
-    val options: DataTrackOptions,
-    rtcTrack: DataChannel
-) : DataTrack(options.name, rtcTrack) {
-    var sid: Sid? = null
+    val options: DataTrackOptions
+) : DataTrack(options.name) {
+    var sid: String? = null
         internal set
-    var cid: Cid = Cid(UUID.randomUUID().toString())
+    var cid: String = UUID.randomUUID().toString()
 
     fun sendString(message: String) {
         val byteBuffer = ByteBuffer.wrap(message.toByteArray())
         val buffer = DataChannel.Buffer(byteBuffer, false)
-        rtcTrack?.send(buffer)
+        dataChannel?.send(buffer)
     }
 
     fun sendBytes(byteBuffer: ByteBuffer) {
         val buffer = DataChannel.Buffer(byteBuffer, true)
-        rtcTrack?.send(buffer)
+        dataChannel?.send(buffer)
     }
-}
\ No newline at end of file
+}

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class LocalDataTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    LocalTrackPublication(info, track), DataTrackPublication {
-    override val dataTrack: DataTrack?
-        get() = track as? DataTrack
-}
\ No newline at end of file

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-open class LocalTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    TrackPublication(info, track) {
-    val localTrack
-        get() = track
-    var priority = Track.Priority.STANDARD
-        private set
-}
\ No newline at end of file

 package io.livekit.android.room.track
 
-data class LocalTrackPublicationOptions(val priority: Track.Priority)
+data class LocalTrackPublicationOptions(val placeholder: Unit)

@@ -16,8 +16,6 @@ class LocalVideoTrack(
         capturer.startCapture(400, 400, 30)
     }
 
-    var sid: Sid? = null
-
     companion object {
         internal fun createTrack(
             peerConnectionFactory: PeerConnectionFactory,

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class LocalVideoTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    LocalTrackPublication(info, track), VideoTrackPublication {
-    override val videoTrack: VideoTrack?
-        get() = track as? VideoTrack
-}

 package io.livekit.android.room.track
 
+import livekit.LivekitModels
 import org.webrtc.MediaStreamTrack
 
-interface MediaTrack {
-    val mediaTrack: MediaStreamTrack
-}
\ No newline at end of file
+
+open class MediaTrack(name: String, kind: LivekitModels.TrackType, open val rtcTrack: MediaStreamTrack) :
+    Track(name, kind) {
+
+    override fun stop() {
+        rtcTrack.setEnabled(false)
+        rtcTrack.dispose()
+    }
+}

 package io.livekit.android.room.track
 
 class RemoteAudioTrack(
-    sid: Sid,
+    sid: String,
     playbackEnabled: Boolean = true,
     name: String,
-    rtcTrack: org.webrtc.AudioTrack
-) : AudioTrack(name, rtcTrack), RemoteTrack {
+    mediaTrack: org.webrtc.AudioTrack
+) : AudioTrack(name, mediaTrack), RemoteTrack {
 
-
-    override var sid: Sid = sid
+    override var sid: String = sid
     var playbackEnabled = playbackEnabled
         internal set
 
-
 }
\ No newline at end of file

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class RemoteAudioTrackPublication(
-    info: LivekitModels.TrackInfo,
-    track: Track? = null
-) : RemoteTrackPublication(info, track), AudioTrackPublication {
-    override val audioTrack: AudioTrack?
-        get() = track as? AudioTrack
-}
\ No newline at end of file

@@ -3,7 +3,7 @@ package io.livekit.android.room.track
 import org.webrtc.DataChannel
 
 class RemoteDataTrack(
-    override var sid: Sid,
+    override var sid: String,
     name: String,
     rtcTrack: DataChannel
 ) :

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class RemoteDataTrackPublication(
-    info: LivekitModels.TrackInfo,
-    track: Track? = null
-) : RemoteTrackPublication(info, track), DataTrackPublication {
-    override val dataTrack: DataTrack?
-        get() = track as? DataTrack
-}
\ No newline at end of file

 package io.livekit.android.room.track
 
 interface RemoteTrack {
-    var sid: Track.Sid
+    var sid: String
 }
\ No newline at end of file

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-open class RemoteTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    TrackPublication(info, track) {
-
-    val remoteTrack: Track?
-        get() = track
-
-    val trackSubscribed: Boolean
-        get() = track != null
-
-    val publishPriority = Track.Priority.STANDARD
-}
\ No newline at end of file

 package io.livekit.android.room.track
 
 class RemoteVideoTrack(
-    override var sid: Sid,
+    override var sid: String,
     var switchedOff: Boolean = false,
-    var priority: Priority? = null,
     name: String,
-    rtcTrack: org.webrtc.VideoTrack
-) : VideoTrack(name, rtcTrack), RemoteTrack
\ No newline at end of file
+    mediaTrack: org.webrtc.VideoTrack
+) : VideoTrack(name, mediaTrack), RemoteTrack

-package io.livekit.android.room.track
-
-import livekit.LivekitModels
-
-class RemoteVideoTrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) :
-    RemoteTrackPublication(info, track),
-    VideoTrackPublication {
-
-    override val videoTrack: VideoTrack?
-        get() = track as? VideoTrack
-}
\ No newline at end of file

 package io.livekit.android.room.track
 
+import livekit.LivekitModels
 import org.webrtc.DataChannel
 import org.webrtc.MediaStreamTrack
 
-open class Track(name: String, state: State) {
-
+open class Track(name: String, kind: LivekitModels.TrackType) {
     var name = name
         internal set
-    var state = state
+    var kind = kind
         internal set
-
-    inline class Sid(val sid: String)
-    inline class Cid(val cid: String)
-
-    enum class Priority {
-        STANDARD, HIGH, LOW;
-    }
+    var state: State = State.NONE
 
     enum class State {
         ENDED, LIVE, NONE;
     }
 
+    open fun stop() {
+        // subclasses override to provide stop behavior
+    }
+
     companion object {
         fun stateFromRTCMediaTrackState(trackState: MediaStreamTrack.State): State {
             return when (trackState) {
@@ -42,6 +40,7 @@ open class Track(name: String, state: State) {
             }
         }
     }
+
 }
 
 sealed class TrackException(message: String? = null, cause: Throwable? = null) :

@@ -5,18 +5,28 @@ import livekit.LivekitModels
 open class TrackPublication(info: LivekitModels.TrackInfo, track: Track? = null) {
     var track: Track? = track
         internal set
-    var trackName: String
+    var name: String
         internal set
-    var trackSid: Track.Sid
+    var sid: String
+        private set
+    var kind: LivekitModels.TrackType
+        private set
+    var muted: Boolean
         private set
 
     init {
-        trackSid = Track.Sid(info.sid)
-        trackName = info.name
+        sid = info.sid
+        name = info.name
+        kind = info.type
+        muted = info.muted
     }
 
     fun updateFromInfo(info: LivekitModels.TrackInfo) {
-        trackSid = Track.Sid(info.sid)
-        trackName = info.name
+        sid = info.sid
+        name = info.name
+        kind = info.type
+
+        // TODO: forward mute status to listener
+        muted = info.muted
     }
-}
\ No newline at end of file
+}

 package io.livekit.android.room.track
 
-import org.webrtc.MediaStreamTrack
+import livekit.LivekitModels
 import org.webrtc.VideoSink
 import org.webrtc.VideoTrack
 
-open class VideoTrack(name: String, val rtcTrack: VideoTrack) :
-    Track(name, stateFromRTCMediaTrackState(rtcTrack.state())),
-    MediaTrack {
-
-    override val mediaTrack: MediaStreamTrack
-        get() = rtcTrack
+open class VideoTrack(name: String, override val rtcTrack: VideoTrack) :
+    MediaTrack(name, LivekitModels.TrackType.VIDEO, rtcTrack){
 
     var enabled: Boolean
         get() = rtcTrack.enabled()
@@ -20,4 +16,4 @@ open class VideoTrack(name: String, val rtcTrack: VideoTrack) :
     fun addRenderer(renderer: VideoSink) = rtcTrack.addSink(renderer)
 
     fun removeRenderer(renderer: VideoSink) = rtcTrack.addSink(renderer)
-}
\ No newline at end of file
+}

-package io.livekit.android.room.track
-
-interface VideoTrackPublication {
-    val videoTrack: VideoTrack?
-}
\ No newline at end of file

@@ -4,19 +4,19 @@ import io.livekit.android.room.participant.Participant
 import io.livekit.android.room.track.Track
 import org.webrtc.DataChannel
 
-fun DataChannel.unpackedTrackLabel(): Triple<Participant.Sid, Track.Sid, String> {
+fun DataChannel.unpackedTrackLabel(): Triple<String, String, String> {
     val parts = label().split("|")
-    val participantSid: Participant.Sid
-    val trackSid: Track.Sid
+    val participantSid: String
+    val trackSid: String
     val name: String
 
     if (parts.count() == 3) {
-        participantSid = Participant.Sid(parts[0])
-        trackSid = Track.Sid(parts[1])
+        participantSid = parts[0]
+        trackSid = parts[1]
         name = parts[2]
     } else {
-        participantSid = Participant.Sid("")
-        trackSid = Track.Sid("")
+        participantSid = ""
+        trackSid = ""
         name = ""
     }
     

@@ -51,7 +51,7 @@ class CallActivity : AppCompatActivity() {
 
                 tabLayoutMediator =
                     TabLayoutMediator(binding.tabs, binding.viewPager) { tab, position ->
-                        tab.text = participants[position].name
+                        tab.text = participants[position].identity
                     }
                 tabLayoutMediator?.attach()
             }

@@ -84,7 +84,7 @@ class CallViewModel(
         mutableRemoteParticipants.postValue(
             room.remoteParticipants
                 .keys
-                .sortedBy { it.sid }
+                .sortedBy { it }
                 .mapNotNull { room.remoteParticipants[it] }
         )
     }

 package io.livekit.android.sample
 
+import android.provider.MediaStore
 import android.view.View
 import com.github.ajalt.timberkt.Timber
 import com.xwray.groupie.viewbinding.BindableItem
 import com.xwray.groupie.viewbinding.GroupieViewHolder
 import io.livekit.android.room.Room
 import io.livekit.android.room.participant.RemoteParticipant
-import io.livekit.android.room.track.RemoteVideoTrackPublication
-import io.livekit.android.room.track.VideoTrack
-import io.livekit.android.room.track.VideoTrackPublication
+import io.livekit.android.room.track.*
 import io.livekit.android.sample.databinding.ParticipantItemBinding
 
 class ParticipantItem(
@@ -30,11 +29,11 @@ class ParticipantItem(
 
             remoteParticipant.listener = object : RemoteParticipant.Listener {
                 override fun onSubscribe(
-                    videoTrack: RemoteVideoTrackPublication,
+                    track: Track,
+                    publication: TrackPublication,
                     participant: RemoteParticipant
                 ) {
-                    val track = videoTrack.videoTrack
-                    if (track != null) {
+                    if (track is VideoTrack) {
                         setupVideoIfNeeded(track, viewBinding)
                     }
                 }
@@ -48,10 +47,8 @@ class ParticipantItem(
 
     private fun getVideoTrack(): VideoTrack? {
         return remoteParticipant
-            .remoteVideoTracks
-            .firstOrNull()
-            .let { it as? VideoTrackPublication }
-            ?.videoTrack
+            .videoTracks.values
+            .firstOrNull()?.track as? VideoTrack
     }
 
     private fun setupVideoIfNeeded(videoTrack: VideoTrack, viewBinding: ParticipantItemBinding) {