new: add playback speed control

core/audioplayer/src/androidMain/kotlin/fr/ajaury/gwenedeg/player/data/AndroidAudioPlayer.kt

@@ -61,6 +61,10 @@ internal class AndroidAudioPlayer(
         player.prepare()
     }
 
+    override fun setSpeed(speed: Float) {
+        player.setPlaybackSpeed(speed)
+    }
+
     override fun play() {
         player.play()
     }

core/audioplayer/src/commonMain/kotlin/fr/ajaury/gwenedeg/player/domain/AudioPlayer.kt

@@ -22,4 +22,7 @@ interface AudioPlayer {
     fun release()
 
     fun load(uri: String)
+
+    /** Sets the playback speed multiplier (e.g. 1.0 for normal speed, 0.5 for half speed). */
+    fun setSpeed(speed: Float)
 }

core/audioplayer/src/iosMain/kotlin/fr/ajaury/gwenedeg/player/data/IosAudioPlayer.kt

@@ -6,14 +6,16 @@ import kotlinx.cinterop.ExperimentalForeignApi
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
+import platform.AVFoundation.AVAudioTimePitchAlgorithmTimeDomain
 import platform.AVFoundation.AVPlayer
 import platform.AVFoundation.AVPlayerItem
 import platform.AVFoundation.AVPlayerItemDidPlayToEndTimeNotification
+import platform.AVFoundation.audioTimePitchAlgorithm
 import platform.AVFoundation.currentItem
 import platform.AVFoundation.currentTime
 import platform.AVFoundation.duration
 import platform.AVFoundation.pause
-import platform.AVFoundation.play
+import platform.AVFoundation.rate
 import platform.AVFoundation.replaceCurrentItemWithPlayerItem
 import platform.AVFoundation.seekToTime
 import platform.CoreMedia.CMTimeGetSeconds
@@ -29,6 +31,7 @@ import kotlin.time.Duration.Companion.seconds
 internal class IosAudioPlayer : AudioPlayer {
     private var player: AVPlayer? = null
     private var endObserver: NSObjectProtocol? = null
+    private var speed: Float = 1f
 
     private val _playbackState = MutableStateFlow(PlaybackState.IDLE)
     override val playbackState: StateFlow<PlaybackState> = _playbackState.asStateFlow()
@@ -63,6 +66,8 @@ internal class IosAudioPlayer : AudioPlayer {
 
         val nsUrl = NSURL.URLWithString(uri) ?: error("Invalid audio URI: $uri")
         val item = AVPlayerItem(uRL = nsUrl)
+        // Time-domain stretching preserves the pitch when the rate is below 1.0.
+        item.audioTimePitchAlgorithm = AVAudioTimePitchAlgorithmTimeDomain
         player = AVPlayer(playerItem = item)
 
         endObserver = NSNotificationCenter.defaultCenter.addObserverForName(
@@ -75,10 +80,18 @@ internal class IosAudioPlayer : AudioPlayer {
     }
 
     override fun play() {
-        player?.play()
+        // Setting a positive rate resumes playback; using the stored speed keeps the chosen tempo.
+        player?.rate = speed
         _playbackState.value = PlaybackState.PLAYING
     }
 
+    override fun setSpeed(speed: Float) {
+        this.speed = speed
+        if (_playbackState.value == PlaybackState.PLAYING) {
+            player?.rate = speed
+        }
+    }
+
     override fun pause() {
         player?.pause()
         _playbackState.value = PlaybackState.PAUSED

core/audioplayer/src/jvmMain/kotlin/fr/ajaury/gwenedeg/player/data/JvmAudioPlayer.kt

@@ -10,6 +10,7 @@ import java.net.URI
 import javax.sound.sampled.AudioFormat
 import javax.sound.sampled.AudioSystem
 import javax.sound.sampled.Clip
+import javax.sound.sampled.FloatControl
 import javax.sound.sampled.LineEvent
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.microseconds
@@ -26,6 +27,9 @@ internal class JvmAudioPlayer : AudioPlayer {
 
     private var stoppedByUser = false
 
+    private var speed: Float = 1f
+    private var baseSampleRate: Float = 0f
+
     private val _playbackState = MutableStateFlow(PlaybackState.IDLE)
     override val playbackState: StateFlow<PlaybackState> = _playbackState.asStateFlow()
 
@@ -77,6 +81,23 @@ internal class JvmAudioPlayer : AudioPlayer {
             }
             open(decodedInput)
         }
+        baseSampleRate = pcmFormat.sampleRate
+        applySpeed()
+    }
+
+    override fun setSpeed(speed: Float) {
+        this.speed = speed
+        applySpeed()
+    }
+
+    /**
+     * Adjusts the tempo through the clip's sample-rate control. Unlike the other platforms this does
+     * not preserve pitch, and it is a no-op when the mixer does not expose the control.
+     */
+    private fun applySpeed() {
+        val clip = clip ?: return
+        if (baseSampleRate <= 0f || !clip.isControlSupported(FloatControl.Type.SAMPLE_RATE)) return
+        (clip.getControl(FloatControl.Type.SAMPLE_RATE) as FloatControl).value = baseSampleRate * speed
     }
 
     override fun play() {

core/audioplayer/src/webMain/kotlin/fr/ajaury/gwenedeg/player/data/WebAudioPlayer.kt

@@ -12,6 +12,7 @@ import kotlin.time.Duration.Companion.seconds
 
 internal class WebAudioPlayer : AudioPlayer {
     private var audio: HTMLAudioElement? = null
+    private var speed: Float = 1f
 
     private val _playbackState = MutableStateFlow(PlaybackState.IDLE)
     override val playbackState: StateFlow<PlaybackState> = _playbackState.asStateFlow()
@@ -31,12 +32,19 @@ internal class WebAudioPlayer : AudioPlayer {
 
         audio = (document.createElement("audio") as HTMLAudioElement).apply {
             src = uri
+            playbackRate = speed.toDouble()
             addEventListener("play") { _playbackState.value = PlaybackState.PLAYING }
             addEventListener("ended") { _playbackState.value = PlaybackState.ENDED }
             addEventListener("pause") { _playbackState.value = PlaybackState.PAUSED }
         }
     }
 
+    override fun setSpeed(speed: Float) {
+        // Browsers preserve pitch (preservesPitch defaults to true) when changing playbackRate.
+        this.speed = speed
+        audio?.playbackRate = speed.toDouble()
+    }
+
     override fun play() {
         audio?.play()
     }