Hold-to-seek acceleration for playback DPAD and seekbar (#900)

## Description
- Adds hold-to-seek acceleration for left/right DPAD input during
playback skip handling.
- Reuses one shared, duration-aware acceleration profile for both
playback DPAD and seekbar skipping.
- Extracts acceleration logic into a shared helper to keep playback and
seekbar behavior consistent.
- Slows the acceleration ramp (about one-third) to improve control
during longer holds.
- Preserves tap-on-release behavior: single taps seek on key release,
while holds seek on repeated key-down without an extra release step.
- Normalizes unknown/unset duration values to use the shortest-content
acceleration profile.
- Added unit coverage for shared seek acceleration math to prevent
accidental regression in ramp thresholds.

### Related issues
Supersedes #846  
Incorporates #784  
Closes #522

### Testing
Tested on Nvidia Shield Pro 2019.

- Quick left/right tap still performs normal skip behavior.
- Holding left/right seeks repeatedly with progressive acceleration.
- Seekbar hold uses the same acceleration profile as playback hold.
- Releasing after a hold does not trigger an extra seek step.

## AI or LLM usage
Codex 5.3 and Claude Opus 4.6 were used for implementation, debugging,
and cross-review. Changes were manually validated on device.

---------

Co-authored-by: Ray <154766448+damontecres@users.noreply.github.com>

app/src/main/java/com/github/damontecres/wholphin/ui/playback/PlaybackKeyHandler.kt

@@ -20,6 +20,7 @@ class PlaybackKeyHandler(
     private val skipWithLeftRight: Boolean,
     private val seekBack: Duration,
     private val seekForward: Duration,
+    private val getDurationMs: () -> Long,
     private val controllerViewState: ControllerViewState,
     private val updateSkipIndicator: (Long) -> Unit,
     private val skipBackOnResume: Duration?,
@@ -28,15 +29,22 @@ class PlaybackKeyHandler(
     private val onStop: () -> Unit,
     private val onPlaybackDialogTypeClick: (PlaybackDialogType) -> Unit,
 ) {
+    private var leftHandledByRepeat = false
+    private var rightHandledByRepeat = false
+
     fun onKeyEvent(it: KeyEvent): Boolean {
         if (it.type == KeyEventType.KeyUp) onInteraction.invoke()
 
-        var result = true
         if (!controlsEnabled) {
-            result = false
+            return false
+        } else if (handleHoldSkip(it)) {
+            return true
         } else if (it.type != KeyEventType.KeyUp) {
-            result = false
-        } else if (isDirectionalDpad(it) || isEnterKey(it) || isControllerMedia(it)) {
+            return false
+        }
+
+        var result = true
+        if (isDirectionalDpad(it) || isEnterKey(it) || isControllerMedia(it)) {
             if (!controllerViewState.controlsVisible) {
                 if (skipWithLeftRight && isSkipBack(it)) {
                     updateSkipIndicator(-seekBack.inWholeMilliseconds)
@@ -111,4 +119,84 @@ class PlaybackKeyHandler(
         }
         return result
     }
+
+    private fun handleHoldSkip(event: KeyEvent): Boolean {
+        if (
+            controllerViewState.controlsVisible ||
+            !skipWithLeftRight ||
+            (!isSkipBack(event) && !isSkipForward(event))
+        ) {
+            return false
+        }
+
+        val isBack = isSkipBack(event)
+        return when (event.type) {
+            KeyEventType.KeyDown -> {
+                val repeatCount = event.nativeKeyEvent.repeatCount
+                if (repeatCount > 0) {
+                    if (repeatCount < HOLD_TO_SEEK_REPEAT_START_COUNT) {
+                        setHandledByRepeat(isBack = isBack, handled = false)
+                        return true
+                    }
+                    val multiplier =
+                        calculateSeekAccelerationMultiplier(
+                            repeatCount = repeatCount - HOLD_TO_SEEK_REPEAT_START_COUNT,
+                            durationMs = normalizedDurationMs(),
+                        )
+                    setHandledByRepeat(isBack = isBack, handled = true)
+                    seekWithMultiplier(isBack = isBack, multiplier = multiplier)
+                } else {
+                    setHandledByRepeat(isBack = isBack, handled = false)
+                }
+                true
+            }
+
+            KeyEventType.KeyUp -> {
+                if (!handledByRepeat(isBack = isBack)) {
+                    seekWithMultiplier(isBack = isBack, multiplier = 1)
+                }
+                setHandledByRepeat(isBack = isBack, handled = false)
+                true
+            }
+
+            else -> {
+                false
+            }
+        }
+    }
+
+    private fun seekWithMultiplier(
+        isBack: Boolean,
+        multiplier: Int,
+    ) {
+        if (isBack) {
+            val skipDuration = seekBack * multiplier
+            player.seekBack(skipDuration)
+            updateSkipIndicator(-skipDuration.inWholeMilliseconds)
+        } else {
+            val skipDuration = seekForward * multiplier
+            player.seekForward(skipDuration)
+            updateSkipIndicator(skipDuration.inWholeMilliseconds)
+        }
+    }
+
+    private fun setHandledByRepeat(
+        isBack: Boolean,
+        handled: Boolean,
+    ) {
+        if (isBack) {
+            leftHandledByRepeat = handled
+        } else {
+            rightHandledByRepeat = handled
+        }
+    }
+
+    private fun handledByRepeat(isBack: Boolean): Boolean =
+        if (isBack) {
+            leftHandledByRepeat
+        } else {
+            rightHandledByRepeat
+        }
+
+    private fun normalizedDurationMs(): Long = getDurationMs().coerceAtLeast(0L)
 }

app/src/main/java/com/github/damontecres/wholphin/ui/playback/PlaybackPage.kt

@@ -235,6 +235,7 @@ fun PlaybackPageContent(
             skipWithLeftRight = true,
             seekForward = preferences.appPreferences.playbackPreferences.skipForwardMs.milliseconds,
             seekBack = preferences.appPreferences.playbackPreferences.skipBackMs.milliseconds,
+            getDurationMs = { player.duration.coerceAtLeast(0L) },
             controllerViewState = controllerViewState,
             updateSkipIndicator = updateSkipIndicator,
             skipBackOnResume = preferences.appPreferences.playbackPreferences.skipBackOnResume,

app/src/main/java/com/github/damontecres/wholphin/ui/playback/SeekAcceleration.kt

@@ -0,0 +1,52 @@
+package com.github.damontecres.wholphin.ui.playback
+
+internal const val HOLD_TO_SEEK_REPEAT_START_COUNT = 12
+
+/**
+ * Shared seek acceleration profile for hold-to-seek behavior.
+ * Keep this in sync anywhere directional key repeat seeking is handled.
+ */
+fun calculateSeekAccelerationMultiplier(
+    repeatCount: Int,
+    durationMs: Long,
+): Int {
+    if (repeatCount <= 0 || durationMs <= 0L) return 1
+
+    // Repeat cadence varies by device. Scaling down by 3 keeps ramp-up closer to multi-second holds.
+    val scaledRepeatCount = repeatCount / 3
+    if (scaledRepeatCount <= 0) return 1
+
+    val durationMinutes = durationMs / 60_000L
+    return when {
+        durationMinutes < 30 -> {
+            if (scaledRepeatCount < 30) 1 else 2
+        }
+
+        durationMinutes < 90 -> {
+            when {
+                scaledRepeatCount < 13 -> 1
+                scaledRepeatCount < 50 -> 2
+                scaledRepeatCount < 75 -> 3
+                else -> 4
+            }
+        }
+
+        durationMinutes < 150 -> {
+            when {
+                scaledRepeatCount < 20 -> 1
+                scaledRepeatCount < 40 -> 2
+                scaledRepeatCount < 60 -> 4
+                else -> 6
+            }
+        }
+
+        else -> {
+            when {
+                scaledRepeatCount < 20 -> 1
+                scaledRepeatCount < 40 -> 3
+                scaledRepeatCount < 60 -> 6
+                else -> 10
+            }
+        }
+    }
+}

app/src/main/java/com/github/damontecres/wholphin/ui/playback/SeekBar.kt

@@ -46,7 +46,6 @@ import androidx.compose.ui.input.key.onPreviewKeyEvent
 import androidx.compose.ui.input.key.type
 import androidx.compose.ui.unit.dp
 import androidx.tv.material3.MaterialTheme
-import com.github.damontecres.wholphin.ui.handleDPadKeyEvents
 import kotlinx.coroutines.FlowPreview
 import kotlin.time.Duration
 
@@ -80,15 +79,16 @@ fun SteppedSeekBarImpl(
         enabled = enabled,
         progress = progressToUse,
         bufferedProgress = bufferedProgress,
-        onLeft = {
+        durationMs = durationMs,
+        onLeft = { multiplier ->
             controllerViewState.pulseControls()
-            seekProgress = (progressToUse - offset).coerceAtLeast(0f)
+            seekProgress = (progressToUse - offset * multiplier).coerceAtLeast(0f)
             hasSeeked = true
             seek(seekProgress)
         },
-        onRight = {
+        onRight = { multiplier ->
             controllerViewState.pulseControls()
-            seekProgress = (progressToUse + offset).coerceAtMost(1f)
+            seekProgress = (progressToUse + offset * multiplier).coerceAtMost(1f)
             hasSeeked = true
             seek(seekProgress)
         },
@@ -126,16 +126,19 @@ fun IntervalSeekBarImpl(
         enabled = enabled,
         progress = (progressToUse.toDouble() / durationMs).toFloat(),
         bufferedProgress = bufferedProgress,
-        onLeft = {
+        durationMs = durationMs,
+        onLeft = { multiplier ->
             controllerViewState.pulseControls()
-            seekPositionMs = (progressToUse - seekBack.inWholeMilliseconds).coerceAtLeast(0L)
+            seekPositionMs =
+                (progressToUse - seekBack.inWholeMilliseconds * multiplier).coerceAtLeast(0L)
             hasSeeked = true
             onSeek(seekPositionMs)
         },
-        onRight = {
+        onRight = { multiplier ->
             controllerViewState.pulseControls()
             seekPositionMs =
-                (progressToUse + seekForward.inWholeMilliseconds).coerceAtMost(durationMs)
+                (progressToUse + seekForward.inWholeMilliseconds * multiplier)
+                    .coerceAtMost(durationMs)
             hasSeeked = true
             onSeek(seekPositionMs)
         },
@@ -148,8 +151,9 @@ fun IntervalSeekBarImpl(
 fun SeekBarDisplay(
     progress: Float,
     bufferedProgress: Float,
-    onLeft: () -> Unit,
-    onRight: () -> Unit,
+    durationMs: Long,
+    onLeft: (Int) -> Unit,
+    onRight: (Int) -> Unit,
     interactionSource: MutableInteractionSource,
     modifier: Modifier = Modifier,
     enabled: Boolean = true,
@@ -158,14 +162,13 @@ fun SeekBarDisplay(
     val onSurface = MaterialTheme.colorScheme.onSurface
 
     val isFocused by interactionSource.collectIsFocusedAsState()
+    var leftHandledByRepeat by remember { mutableStateOf(false) }
+    var rightHandledByRepeat by remember { mutableStateOf(false) }
     val animatedIndicatorHeight by animateDpAsState(
         targetValue = 6.dp.times((if (isFocused) 2f else 1f)),
     )
 
-    Column(
-        modifier = modifier,
-        verticalArrangement = Arrangement.spacedBy(16.dp),
-    ) {
+    Column(modifier = modifier, verticalArrangement = Arrangement.spacedBy(16.dp)) {
         Canvas(
             modifier =
                 Modifier
@@ -173,24 +176,79 @@ fun SeekBarDisplay(
                     .height(animatedIndicatorHeight)
                     .padding(horizontal = 4.dp)
                     .onPreviewKeyEvent { event ->
-                        val trigger =
-                            event.type == KeyEventType.KeyUp || event.nativeKeyEvent.repeatCount > 0
                         when (event.nativeKeyEvent.keyCode) {
                             KeyEvent.KEYCODE_DPAD_LEFT, KeyEvent.KEYCODE_SYSTEM_NAVIGATION_LEFT -> {
-                                if (trigger) onLeft.invoke()
+                                when (event.type) {
+                                    KeyEventType.KeyDown -> {
+                                        val repeatCount = event.nativeKeyEvent.repeatCount
+                                        if (repeatCount > 0) {
+                                            if (repeatCount < HOLD_TO_SEEK_REPEAT_START_COUNT) {
+                                                leftHandledByRepeat = false
+                                                return@onPreviewKeyEvent true
+                                            }
+                                            leftHandledByRepeat = true
+                                            onLeft.invoke(
+                                                calculateSeekAccelerationMultiplier(
+                                                    repeatCount = repeatCount - HOLD_TO_SEEK_REPEAT_START_COUNT,
+                                                    durationMs = durationMs,
+                                                ),
+                                            )
+                                        } else {
+                                            leftHandledByRepeat = false
+                                        }
+                                    }
+
+                                    KeyEventType.KeyUp -> {
+                                        if (!leftHandledByRepeat) {
+                                            onLeft.invoke(1)
+                                        }
+                                        leftHandledByRepeat = false
+                                    }
+
+                                    else -> {
+                                        return@onPreviewKeyEvent false
+                                    }
+                                }
                                 return@onPreviewKeyEvent true
                             }
 
                             KeyEvent.KEYCODE_DPAD_RIGHT, KeyEvent.KEYCODE_SYSTEM_NAVIGATION_RIGHT -> {
-                                if (trigger) onRight.invoke()
+                                when (event.type) {
+                                    KeyEventType.KeyDown -> {
+                                        val repeatCount = event.nativeKeyEvent.repeatCount
+                                        if (repeatCount > 0) {
+                                            if (repeatCount < HOLD_TO_SEEK_REPEAT_START_COUNT) {
+                                                rightHandledByRepeat = false
+                                                return@onPreviewKeyEvent true
+                                            }
+                                            rightHandledByRepeat = true
+                                            onRight.invoke(
+                                                calculateSeekAccelerationMultiplier(
+                                                    repeatCount = repeatCount - HOLD_TO_SEEK_REPEAT_START_COUNT,
+                                                    durationMs = durationMs,
+                                                ),
+                                            )
+                                        } else {
+                                            rightHandledByRepeat = false
+                                        }
+                                    }
+
+                                    KeyEventType.KeyUp -> {
+                                        if (!rightHandledByRepeat) {
+                                            onRight.invoke(1)
+                                        }
+                                        rightHandledByRepeat = false
+                                    }
+
+                                    else -> {
+                                        return@onPreviewKeyEvent false
+                                    }
+                                }
                                 return@onPreviewKeyEvent true
                             }
                         }
                         false
-                    }.handleDPadKeyEvents(
-                        onLeft = onLeft,
-                        onRight = onRight,
-                    ).focusable(enabled = enabled, interactionSource = interactionSource),
+                    }.focusable(enabled = enabled, interactionSource = interactionSource),
             onDraw = {
                 val yOffset = size.height.div(2)
                 drawLine(

app/src/test/java/com/github/damontecres/wholphin/ui/playback/SeekAccelerationTest.kt

@@ -0,0 +1,53 @@
+package com.github.damontecres.wholphin.ui.playback
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class SeekAccelerationTest {
+    @Test
+    fun returnsOneWhenNotRepeating() {
+        assertEquals(1, calculateSeekAccelerationMultiplier(repeatCount = 0, durationMs = 30_000L))
+    }
+
+    @Test
+    fun unknownDurationDoesNotAccelerate() {
+        assertEquals(1, calculateSeekAccelerationMultiplier(repeatCount = 89, durationMs = 0L))
+        assertEquals(1, calculateSeekAccelerationMultiplier(repeatCount = 300, durationMs = -1L))
+    }
+
+    @Test
+    fun shortContentHasTwoTiers() {
+        val shortDurationMs = 20L * 60_000L
+
+        assertEquals(
+            1,
+            calculateSeekAccelerationMultiplier(repeatCount = 89, durationMs = shortDurationMs),
+        )
+        assertEquals(
+            2,
+            calculateSeekAccelerationMultiplier(repeatCount = 90, durationMs = shortDurationMs),
+        )
+    }
+
+    @Test
+    fun mediumContentEscalatesAcrossAllTiers() {
+        val mediumDurationMs = 60L * 60_000L
+
+        assertEquals(
+            1,
+            calculateSeekAccelerationMultiplier(repeatCount = 38, durationMs = mediumDurationMs),
+        )
+        assertEquals(
+            2,
+            calculateSeekAccelerationMultiplier(repeatCount = 39, durationMs = mediumDurationMs),
+        )
+        assertEquals(
+            3,
+            calculateSeekAccelerationMultiplier(repeatCount = 150, durationMs = mediumDurationMs),
+        )
+        assertEquals(
+            4,
+            calculateSeekAccelerationMultiplier(repeatCount = 225, durationMs = mediumDurationMs),
+        )
+    }
+}