Add variable playback speed feature for voice messages

Add playback speed control for voice messages with support for 0.5×, 1×, 1.5×, and 2× playback speeds. The speed button is displayed above the timestamp and cycles through the available speeds when tapped.

libraries/voiceplayer/impl/src/main/kotlin/io/element/android/libraries/voiceplayer/impl/VoiceMessagePlayer.kt

@@ -79,6 +79,13 @@ interface VoiceMessagePlayer {
      */
     fun seekTo(positionMs: Long)
 
+    /**
+     * Set the playback speed.
+     *
+     * @param speed The playback speed (e.g., 0.5f for half speed, 1.0f for normal, 2.0f for double speed)
+     */
+    fun setPlaybackSpeed(speed: Float)
+
     data class State(
         /**
          * Whether the player is ready to play.
@@ -218,6 +225,10 @@ class Factory(
         }
     }
 
+    override fun setPlaybackSpeed(speed: Float) {
+        mediaPlayer.setPlaybackSpeed(speed)
+    }
+
     private val MediaPlayer.State.isMyTrack: Boolean
         get() = if (eventId == null) false else this.mediaId == eventId.value
 

libraries/voiceplayer/impl/src/main/kotlin/io/element/android/libraries/voiceplayer/impl/VoiceMessagePresenter.kt

@@ -37,6 +37,9 @@ class VoiceMessagePresenter(
     private val duration: Duration,
 ) : Presenter<VoiceMessageState> {
     private val play = mutableStateOf<AsyncData<Unit>>(AsyncData.Uninitialized)
+    private val playbackSpeed = mutableStateOf(1.0f)
+
+    private val availablePlaybackSpeeds = listOf(0.5f, 1.0f, 1.5f, 2.0f)
 
     @Composable
     override fun present(): VoiceMessageState {
@@ -111,6 +114,13 @@ class VoiceMessagePresenter(
                 is VoiceMessageEvents.Seek -> {
                     player.seekTo((event.percentage * duration).toLong())
                 }
+                is VoiceMessageEvents.ChangePlaybackSpeed -> {
+                    val currentIndex = availablePlaybackSpeeds.indexOf(playbackSpeed.value)
+                    val nextIndex = (currentIndex + 1) % availablePlaybackSpeeds.size
+                    val newSpeed = availablePlaybackSpeeds[nextIndex]
+                    playbackSpeed.value = newSpeed
+                    player.setPlaybackSpeed(newSpeed)
+                }
             }
         }
 
@@ -119,6 +129,7 @@ class VoiceMessagePresenter(
             progress = progress,
             time = time,
             showCursor = showCursor,
+            playbackSpeed = playbackSpeed.value,
             eventSink = { eventSink(it) },
         )
     }

libraries/voiceplayer/impl/src/test/kotlin/io/element/android/libraries/voiceplayer/impl/VoiceMessagePresenterTest.kt

@@ -222,6 +222,40 @@ class VoiceMessagePresenterTest {
             }
         }
     }
+
+    @Test
+    fun `changing playback speed cycles through available speeds`() = runTest {
+        val presenter = createVoiceMessagePresenter(
+            duration = 10_000.milliseconds,
+        )
+        moleculeFlow(RecompositionMode.Immediate) {
+            presenter.present()
+        }.test {
+            val initialState = awaitItem().also {
+                assertThat(it.playbackSpeed).isEqualTo(1.0f)
+            }
+
+            initialState.eventSink(VoiceMessageEvents.ChangePlaybackSpeed)
+            awaitItem().also {
+                assertThat(it.playbackSpeed).isEqualTo(1.5f)
+            }
+
+            initialState.eventSink(VoiceMessageEvents.ChangePlaybackSpeed)
+            awaitItem().also {
+                assertThat(it.playbackSpeed).isEqualTo(2.0f)
+            }
+
+            initialState.eventSink(VoiceMessageEvents.ChangePlaybackSpeed)
+            awaitItem().also {
+                assertThat(it.playbackSpeed).isEqualTo(0.5f)
+            }
+
+            initialState.eventSink(VoiceMessageEvents.ChangePlaybackSpeed)
+            awaitItem().also {
+                assertThat(it.playbackSpeed).isEqualTo(1.0f)
+            }
+        }
+    }
 }
 
 fun TestScope.createVoiceMessagePresenter(