feat(subtitles): optionally anchor text subtitles to the screen bottom

Adds an "Anchor to Screen" toggle under Subtitle Styling (Android +
ExoPlayer only, default off). When enabled, the text SubtitleView is
sized to the full container instead of the letterboxed video rect, so
SRT/VTT/mov_text cues render in the black bars below widescreen video
and font size and the position setting become relative to the physical
screen height. Bitmap (PGS/VOB) and ASS/libass rendering are unchanged;
mpv already places plaintext subtitles in the margins by default.

close #1730

android/app/src/main/kotlin/com/edde746/plezy/exoplayer/ExoPlayerCore.kt

@@ -215,6 +215,7 @@ class ExoPlayerCore(private val activity: Activity) :
   @Volatile private var assVideoLatencyFrames = 0
   private var subtitlePositionPercent: Int = 100
   private var subtitleFontSize: Float = 55f
+  private var subtitleAnchorToScreen: Boolean = false
   private var lastSubtitleCues: List<Cue> = emptyList()
 
   // Tracks whether a text track was selected on the previous onTracksChanged so we
@@ -1757,7 +1758,8 @@ class ExoPlayerCore(private val activity: Activity) :
       videoHeight,
       pixelRatio,
       resizeMode,
-      videoZoomScale
+      videoZoomScale,
+      subtitleAnchorToScreen
     )
     val bitmapDimensions = SubtitleViewLayout.bitmapDimensions(
       containerWidth,
@@ -3911,7 +3913,8 @@ class ExoPlayerCore(private val activity: Activity) :
     bgOpacity: Int,
     subtitlePosition: Int = 100,
     bold: Boolean = false,
-    italic: Boolean = false
+    italic: Boolean = false,
+    anchorToScreen: Boolean = false
   ) {
     activity.runOnUiThread {
       // 1. Non-ASS subtitles: CaptionStyleCompat on SubtitleView
@@ -3959,6 +3962,18 @@ class ExoPlayerCore(private val activity: Activity) :
       subtitlePositionPercent = clampedPosition
       subtitleFontSize = fontSize
 
+      // Anchor-to-screen (#1730): resize the text SubtitleView to the full
+      // container so default-placed cues land in the letterbox bars.
+      val anchorChanged = subtitleAnchorToScreen != anchorToScreen
+      subtitleAnchorToScreen = anchorToScreen
+      if (anchorChanged) {
+        lastVideoSize?.let { vs ->
+          if (vs.width > 0 && vs.height > 0) {
+            updateSubtitleViewSize(vs.width, vs.height, vs.pixelWidthHeightRatio)
+          }
+        }
+      }
+
       // Cue-level positioning handles default VTT/SRT placement, whose line
       // numbers bypass SubtitleView bottom padding. Authored VTT line positions
       // are preserved in applySubtitlePosition().
@@ -3980,7 +3995,7 @@ class ExoPlayerCore(private val activity: Activity) :
         Log.w(TAG, "Failed to set ASS font scale: ${e.message}")
       }
 
-      Log.d(TAG, "setSubtitleStyle: fontSize=$fontSize, textColor=$textColor, borderSize=$borderSize, bgOpacity=$bgOpacity, position=$subtitlePosition, bold=$bold, italic=$italic, assScale=$scale")
+      Log.d(TAG, "setSubtitleStyle: fontSize=$fontSize, textColor=$textColor, borderSize=$borderSize, bgOpacity=$bgOpacity, position=$subtitlePosition, bold=$bold, italic=$italic, anchorToScreen=$anchorToScreen, assScale=$scale")
     }
   }
 

android/app/src/main/kotlin/com/edde746/plezy/exoplayer/ExoPlayerPlugin.kt

@@ -1069,6 +1069,7 @@ class ExoPlayerPlugin :
     val subtitlePosition = call.argument<Number>("subtitlePosition")?.toInt() ?: 100
     val bold = call.argument<Boolean>("bold") ?: false
     val italic = call.argument<Boolean>("italic") ?: false
+    val anchorToScreen = call.argument<Boolean>("anchorToScreen") ?: false
 
     if (usingMpvFallback) {
       // MPV fallback handles styling via setProperty, no-op here
@@ -1076,7 +1077,7 @@ class ExoPlayerPlugin :
       return
     }
 
-    playerCore?.setSubtitleStyle(fontSize, textColor, borderSize, borderColor, bgColor, bgOpacity, subtitlePosition, bold, italic)
+    playerCore?.setSubtitleStyle(fontSize, textColor, borderSize, borderColor, bgColor, bgOpacity, subtitlePosition, bold, italic, anchorToScreen)
     result.success(null)
   }
 

android/app/src/main/kotlin/com/edde746/plezy/exoplayer/SubtitleViewLayout.kt

@@ -13,12 +13,18 @@ internal object SubtitleViewLayout {
     videoHeight: Int,
     pixelRatio: Float,
     resizeMode: Int,
-    zoomScale: Float
+    zoomScale: Float,
+    anchorToScreen: Boolean = false
   ): SubtitleViewDimensions? {
     val videoAspect = videoAspect(videoWidth, videoHeight, pixelRatio) ?: return null
     if (containerWidth <= 0 || containerHeight <= 0) return null
 
-    if (resizeMode != AspectRatioFrameLayout.RESIZE_MODE_FIT) {
+    // Anchor-to-screen (#1730): size the text view to the full container so
+    // media3's fractional text size and bottom-anchored cue placement compute
+    // against the physical screen, letting subtitles render in the letterbox
+    // bars instead of inside the video rect. Same geometry the non-FIT modes
+    // below already use.
+    if (anchorToScreen || resizeMode != AspectRatioFrameLayout.RESIZE_MODE_FIT) {
       return SubtitleViewDimensions(containerWidth, containerHeight)
     }
 

android/app/src/test/kotlin/com/edde746/plezy/exoplayer/SubtitleViewLayoutTest.kt

@@ -45,9 +45,49 @@ class SubtitleViewLayoutTest {
     assertAspectCloseTo16By9(bitmap!!)
   }
 
+  @Test
+  fun anchorToScreenSizesTextToContainerAndKeepsBitmapOnVideoRect() {
+    val text = textDimensions(resizeMode = AspectRatioFrameLayout.RESIZE_MODE_FIT, anchorToScreen = true)
+    val bitmap = bitmapDimensions(resizeMode = AspectRatioFrameLayout.RESIZE_MODE_FIT)
+
+    assertEquals(SubtitleViewDimensions(2424, 1080), text)
+    assertEquals(SubtitleViewDimensions(1920, 1080), bitmap)
+    assertAspectCloseTo16By9(bitmap!!)
+  }
+
+  @Test
+  fun anchorToScreenReachesBelowLetterboxedWideVideo() {
+    // 2.37:1 video on a 16:9 screen — the #1730 use case. Without the anchor
+    // the text view stops at the bottom letterbox bar; with it the view spans
+    // the physical screen height.
+    val unanchored = SubtitleViewLayout.textDimensions(
+      containerWidth = 1920,
+      containerHeight = 1080,
+      videoWidth = 2560,
+      videoHeight = 1080,
+      pixelRatio = 1f,
+      resizeMode = AspectRatioFrameLayout.RESIZE_MODE_FIT,
+      zoomScale = 1f
+    )
+    val anchored = SubtitleViewLayout.textDimensions(
+      containerWidth = 1920,
+      containerHeight = 1080,
+      videoWidth = 2560,
+      videoHeight = 1080,
+      pixelRatio = 1f,
+      resizeMode = AspectRatioFrameLayout.RESIZE_MODE_FIT,
+      zoomScale = 1f,
+      anchorToScreen = true
+    )
+
+    assertEquals(SubtitleViewDimensions(1920, 810), unanchored)
+    assertEquals(SubtitleViewDimensions(1920, 1080), anchored)
+  }
+
   private fun textDimensions(
     resizeMode: Int,
-    zoomScale: Float = 1f
+    zoomScale: Float = 1f,
+    anchorToScreen: Boolean = false
   ): SubtitleViewDimensions? = SubtitleViewLayout.textDimensions(
     containerWidth = 2424,
     containerHeight = 1080,
@@ -55,7 +95,8 @@ class SubtitleViewLayoutTest {
     videoHeight = 1080,
     pixelRatio = 1f,
     resizeMode = resizeMode,
-    zoomScale = zoomScale
+    zoomScale = zoomScale,
+    anchorToScreen = anchorToScreen
   )
 
   private fun bitmapDimensions(