android, desktop: fix video preview expanding into empty black area (#7286)

* android, desktop: fix video preview expanding into empty black area

The video message box (CHAT_IMAGE_LAYOUT_ID) never gave itself a definite
height - it took the height of its tallest child. That child is the player
surface, which has no stable intrinsic height until playback starts: on
Android an unprepared StyledPlayerView reports no video size, so its
AspectRatioFrameLayout (RESIZE_MODE_FIXED_WIDTH, aspect 0) does not shrink.

Before #6726 this was masked: the box was measured with unbounded height, so
the surface collapsed to 0. #6726 bounded the box to 2.33x width to constrain
tall images, and the unprepared surface then expanded to fill that height,
showing as a long empty black strip below the preview once a video downloads.

Give the box a definite size from the preview aspect ratio, mirroring
CIImageView. Height follows the measured (clamped) width via Modifier.layout
so wide videos on narrow screens don't leave an empty strip (the #7223 fix).

* plans: justify video preview black-area fix

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/item/CIVideoView.kt

@@ -25,6 +25,7 @@ import chat.simplex.common.views.chat.chatViewScrollState
 import dev.icerock.moko.resources.StringResource
 import java.io.File
 import java.net.URI
+import kotlin.math.roundToInt
 
 @Composable
 fun CIVideoView(
@@ -38,12 +39,25 @@ fun CIVideoView(
   receiveFile: (Long) -> Unit
 ) {
   val blurred = remember { mutableStateOf(appPrefs.privacyMediaBlurRadius.get() > 0) }
+  val preview = remember(image) { base64ToBitmap(image) }
   Box(
     Modifier.layoutId(CHAT_IMAGE_LAYOUT_ID)
+      .then(
+        if (!smallView) {
+          val w = if (preview.width * 0.97 <= preview.height) videoViewFullWidth(LocalWindowWidth()) * 0.75f else DEFAULT_MAX_IMAGE_WIDTH
+          // Size the media box from the preview aspect ratio (as CIImageView does), else the unprepared player surface
+          // expands to PriorityLayout's max height and shows as a black strip; height tracks the clamped width (#7223).
+          Modifier.width(w).layout { measurable, constraints ->
+            val width = constraints.maxWidth.coerceAtMost(w.roundToPx().coerceAtLeast(0))
+            val height = (width * (preview.height.toFloat() / preview.width.toFloat()).coerceAtMost(2.33f)).roundToInt().coerceAtMost(constraints.maxHeight)
+            val placeable = measurable.measure(Constraints.fixed(width, height))
+            layout(width, height) { placeable.place(0, 0) }
+          }
+        } else Modifier
+      )
       .desktopModifyBlurredState(!smallView, blurred, showMenu),
     contentAlignment = Alignment.TopEnd
   ) {
-    val preview = remember(image) { base64ToBitmap(image) }
     val filePath = remember(file, CIFile.cachedRemoteFileRequests.toList()) { mutableStateOf(getLoadedFilePath(file)) }
     val sizeMultiplier = if (smallView) 0.38f else 1f
     if (chatModel.connectedToRemote()) {

plans/2026-07-21-fix-video-preview-black-area.md

@@ -0,0 +1,70 @@
+# Fix: video preview expands into a long empty black area
+
+## Problem
+
+On Android, once a video message finishes downloading, its in-chat preview grows
+into a tall empty black area below the thumbnail. It appears the moment the file
+download completes (before playback), and is worst for landscape videos.
+
+## Root cause
+
+The video message renders into the shared `CHAT_IMAGE_LAYOUT_ID` box measured by
+`PriorityLayout` (`FramedItemView.kt`). Unlike `CIImageView`, `CIVideoView` never
+gave that box a definite size — it inherited the height of its tallest child.
+
+Once downloaded, the tallest child is the player surface. On Android that is a
+`StyledPlayerView` with `RESIZE_MODE_FIXED_WIDTH`. Before playback the player is
+unprepared (the media source is only set in `VideoPlayer.start()`, called from
+`play()`), so it reports no video size and its `AspectRatioFrameLayout` keeps
+aspect ratio 0 and does **not** shrink its height.
+
+This was latent until #6726 ("constrain image sizes for previews"). That change
+bounded the box to `maxHeight = 2.33 × width` to tame extreme image aspect
+ratios. Before it, the box was measured with unbounded height, so on Android the
+unprepared surface collapsed to 0 (`getDefaultSize` with an `UNSPECIFIED` spec)
+and contributed no height — accidentally masking the missing-size flaw. After
+#6726 the surface expands to fill the now-bounded `2.33 × width`, showing as a
+long black strip behind the shorter thumbnail.
+
+The later image fixes (#7123 / #7125 / #7223) all touched `CIImageView` only, so
+video was never given a definite box size and kept the defect.
+
+## Fix
+
+Give `CIVideoView`'s `CHAT_IMAGE_LAYOUT_ID` box a definite size derived from the
+preview aspect ratio, mirroring `CIImageView`. Height is computed from the
+*measured* (clamped) width via `Modifier.width(w).layout { … }`, not the nominal
+width, so a wide video whose nominal `w = DEFAULT_MAX_IMAGE_WIDTH` (500dp) is
+clamped on a narrower screen does not leave an empty strip below — the same
+correction #7223 applied to images. Applied only for `!smallView`; the small
+chat-list thumbnail (`smallView = true`) keeps its existing sizing.
+
+With the box sized to the preview footprint, the player surface can no longer
+expand past it (its bounded max height now equals the thumbnail height), and the
+opaque preview drawn on top exactly covers it. When playing, `RESIZE_MODE_FIXED_WIDTH`
+conforms the surface to the real video aspect, which matches the thumbnail.
+
+## Alternatives considered
+
+- **Force the Android `StyledPlayerView` aspect from the preview.** Android-only;
+  treats one render backend and leaves the box height still child-dependent — a
+  workaround at the wrong layer.
+- **Only mount `PlayerView` while playing.** Larger behavioural change; risks the
+  play/preview transition blinking the code already guards against; does not
+  establish the container invariant.
+- **`matchParentSize()` on the player.** Breaks: when playing, the preview is
+  removed, so no sibling defines the box and it collapses to 0.
+- **Naive `Modifier.width(w).height(w * ratio)`.** Reintroduces the exact #7223
+  empty-strip bug for wide videos on screens narrower than 500dp.
+
+The chosen fix restores the invariant "a media chat item occupies exactly the
+media's aspect-ratio footprint" at the correct layer (the media container), for
+all render states (pre-download / downloaded-idle / playing / encrypted) and both
+platforms, using the same aspect source the player conforms to.
+
+## Verification
+
+- `android:assembleDebug` (arm64 debug APK) — BUILD SUCCESSFUL.
+- Desktop `createDistributable` + AppImage (Linux x86_64) — BUILD SUCCESSFUL.
+- Control APK built from the same base without the fix, to A/B the black area
+  against the fixed build (both `7.0-beta.4`, differing only by this change).