diff --git a/MainWindow.xaml b/MainWindow.xaml
index 8a2100d..d908a57 100644
--- a/MainWindow.xaml
+++ b/MainWindow.xaml
@@ -377,6 +377,31 @@
                                                  HorizontalAlignment="Right" VerticalAlignment="Bottom" Margin="0,0,-13,-13"/>
                                     </Grid>
 
+                                    <ItemsControl ItemsSource="{Binding DimRects}" IsHitTestVisible="False">
+                                        <ItemsControl.ItemsPanel>
+                                            <ItemsPanelTemplate>
+                                                <Canvas/>
+                                            </ItemsPanelTemplate>
+                                        </ItemsControl.ItemsPanel>
+                                        <ItemsControl.ItemContainerStyle>
+                                            <Style TargetType="ContentPresenter">
+                                                <Setter Property="Canvas.Left" Value="{Binding X}"/>
+                                                <Setter Property="Canvas.Top" Value="{Binding Y}"/>
+                                            </Style>
+                                        </ItemsControl.ItemContainerStyle>
+                                        <ItemsControl.ItemTemplate>
+                                            <DataTemplate>
+                                                <Rectangle Width="{Binding Width}" Height="{Binding Height}"
+                                                           Fill="#000000" Opacity="0.55"/>
+                                            </DataTemplate>
+                                        </ItemsControl.ItemTemplate>
+                                    </ItemsControl>
+
+                                    <Rectangle IsHitTestVisible="False" Stroke="#e94560" StrokeThickness="3"
+                                               Canvas.Left="{Binding OutputRectX}" Canvas.Top="{Binding OutputRectY}"
+                                               Width="{Binding OutputRectWidth}" Height="{Binding OutputRectHeight}"
+                                               Visibility="{Binding IsOutputCropped, Converter={StaticResource BoolToVis}}"/>
+
                                     <Grid x:Name="BrandFlashLayer" Width="1920" Height="1080" IsHitTestVisible="False" Opacity="0">
                                         <Grid.Style>
                                             <Style TargetType="Grid">
@@ -412,6 +437,10 @@
                                 </Canvas>
                             </Grid>
                         </Viewbox>
+                        <Border HorizontalAlignment="Right" VerticalAlignment="Top" Margin="0,8,8,0"
+                                Background="#CC16213e" CornerRadius="4" Padding="8,3" IsHitTestVisible="False">
+                            <TextBlock Text="{Binding ResolutionBadgeText}" Foreground="#e0e0e0" FontSize="12"/>
+                        </Border>
                         <TextBlock Text="Preview" Foreground="#333" FontSize="24"
                                    HorizontalAlignment="Center" VerticalAlignment="Center"
                                    Visibility="{Binding ShowPreviewPlaceholder, Converter={StaticResource BoolToVis}}"/>
diff --git a/Models/QualityOption.cs b/Models/QualityOption.cs
index 229626e..54c12f4 100644
--- a/Models/QualityOption.cs
+++ b/Models/QualityOption.cs
@@ -2,8 +2,10 @@ namespace ytLive.Models;
 
 /// <summary>
 /// A resolution tier offered by the bottom-bar dropdown. Bitrate is Mbps.
+/// Width/Height is the output frame; the composition master is always
+/// 1920x1080 and a non-16:9 tier renders as a centered crop of it.
 /// </summary>
-public sealed record QualityOption(string Display, int Fps, double Bitrate)
+public sealed record QualityOption(string Display, int Fps, double Bitrate, int Width, int Height)
 {
     /// <summary>Self-documenting label, e.g. "1080p60 (8Mbps)".</summary>
     public string Label => $"{Display} ({Bitrate:0.#}Mbps)";
diff --git a/Models/index.md b/Models/index.md
index 66768db..8b67af9 100644
--- a/Models/index.md
+++ b/Models/index.md
@@ -7,7 +7,7 @@ Plain data types. No logic beyond what a property can carry. See
 |------|---------|
 | `Scene.cs` | A scene: `Name`, `IsHidden`, `IsChatScene`, `IsEditing`, `Sources` collection |
 | `Source.cs` | A source: `SourceType` enum (Image/Webcam/Screen/Background/Text), `X`/`Y`/`Width`/`Height`, `Opacity`, `IsEnabled`, `ImageSource`, asset identity |
-| `QualityOption.cs` | Resolution tier record `(Display, Fps, Bitrate)`; `Label` formats as `1080p60 (8Mbps)` — drives the bottom-bar dropdown |
+| `QualityOption.cs` | Resolution tier record `(Display, Fps, Bitrate, Width, Height)`; `Label` formats as `1080p60 (8Mbps)` — drives the bottom-bar dropdown and the output-rect math |
 | `StreamConfig.cs` | `StreamConfig` (note: `TargetBitrate`/`Resolution` defaults are stale — not yet wired to the dropdown), `StreamHealth` (bitrate/FPS/dropped/duration), `StreamStatus` enum |
 | `YouTube.cs` | `YouTubeChannel` and `ChatMessage` (chat feed) |
 
diff --git a/TASKS.md b/TASKS.md
index 0e77ba0..00dbff9 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -162,12 +162,16 @@ Preview shows the transition too (WYSIWYG). No wipes/slides/LUTs beyond the four
 1. **Encoding** — H.264 (hardware via NVENC/AMD, fallback x264) + AAC audio; **must comply**: keyframes ≤ 4s (gopSizeLong), closed GOP, AAC/MP3 @ 44.1/48kHz, mono/stereo only
 2. **RTMP push** — FFmpeg subprocess or native RTMP library, to the cached reusable stream's ingestion URL
 3. **Quality ladder** — the offered tiers, with **1080p60 @ 8 Mbps as the standard/default**:
-   - Phone 480p @ 2.5 Mbps
+   - 720p30 @ 6 Mbps
    - 720p60 @ 6 Mbps
    - 1080p30 @ 8 Mbps
    - **1080p60 @ 8 Mbps** (default — mainstream ceiling, GPU hardware-encoded so the gaming
      machine never notices; upload headroom stays comfortable)
+   - Vertical 1080×1920 @ 60fps @ 8 Mbps (9:16 phone tier)
    - 1440p/4K = the paid unlock tiers (monetization), not the standard offering
+   The composition master is always 1920×1080; a tier is an output rect + target resolution
+   (see `ai.md` "Resolution tiers"). Vertical output = the centered 607×1080 crop of the master
+   scaled to 1080×1920 (semi-crop preview is already implemented; the encoder applies the same rect).
    Ladder is sculpted by a **cached probe** (IP-only TCP vs public ingest host; no auth required).
    Quality is greyed out while live because the declared resolution can't change mid-stream — but
    with `variable`, we can **auto step-down** bitrate/resolution on the fly with zero API calls
diff --git a/ViewModels/MainViewModel.cs b/ViewModels/MainViewModel.cs
index 0ccd1a6..87d7774 100644
--- a/ViewModels/MainViewModel.cs
+++ b/ViewModels/MainViewModel.cs
@@ -295,12 +295,20 @@ public class MainViewModel : ViewModelBase
     // dropdown is disabled while live because YouTube stream resolution is
     // immutable after stream creation (see TASKS.md compliance notes).
 
+    // The composition master frame. Every tier is an output rect + target
+    // resolution over this frame (see ai.md "Resolution tiers"): 16:9 tiers
+    // use the full frame; the vertical tier uses a centered 9:16 window and
+    // the preview dims the cropped strips (semi-crop).
+    private const double MasterFrameWidth = 1920;
+    private const double MasterFrameHeight = 1080;
+
     public QualityOption[] QualityOptions { get; } =
     {
-        new("1080p60", 60, 8.0),
-        new("1080p30", 30, 8.0),
-        new("720p60", 60, 6.0),
-        new("480p30", 30, 2.5),
+        new("1080p60", 60, 8.0, 1920, 1080),
+        new("1080p30", 30, 8.0, 1920, 1080),
+        new("720p60", 60, 6.0, 1280, 720),
+        new("720p30", 30, 6.0, 1280, 720),
+        new("Vertical 1080p60", 60, 8.0, 1080, 1920),
     };
 
     public string ResolutionHelp { get; } =
@@ -319,12 +327,51 @@ public class MainViewModel : ViewModelBase
         }
     }
 
+    // Output frame of the selected tier over the 1920x1080 master. The strips
+    // outside it are dimmed in the preview so the cropped area stays visible.
+    public double OutputRectX { get; private set; }
+    public double OutputRectY { get; private set; }
+    public double OutputRectWidth { get; private set; }
+    public double OutputRectHeight { get; private set; }
+    public bool IsOutputCropped { get; private set; }
+    public string ResolutionBadgeText { get; private set; } = string.Empty;
+    public ObservableCollection<Rect> DimRects { get; } = new();
+
     private void ApplyStreamQuality(QualityOption quality)
     {
         var health = CurrentHealth;
         health.CurrentBitrate = quality.Bitrate;
         health.FPS = quality.Fps;
         OnPropertyChanged(nameof(CurrentHealth));
+
+        var scale = Math.Min(MasterFrameWidth / quality.Width, MasterFrameHeight / quality.Height);
+        var rectW = quality.Width * scale;
+        var rectH = quality.Height * scale;
+        var rectX = (MasterFrameWidth - rectW) / 2;
+        var rectY = (MasterFrameHeight - rectH) / 2;
+
+        OutputRectX = rectX;
+        OutputRectY = rectY;
+        OutputRectWidth = rectW;
+        OutputRectHeight = rectH;
+
+        DimRects.Clear();
+        if (rectX > 0) DimRects.Add(new Rect(0, 0, rectX, MasterFrameHeight));
+        if (rectX + rectW < MasterFrameWidth)
+            DimRects.Add(new Rect(rectX + rectW, 0, MasterFrameWidth - rectX - rectW, MasterFrameHeight));
+        if (rectY > 0) DimRects.Add(new Rect(0, 0, MasterFrameWidth, rectY));
+        if (rectY + rectH < MasterFrameHeight)
+            DimRects.Add(new Rect(0, rectY + rectH, MasterFrameWidth, MasterFrameHeight - rectY - rectH));
+
+        IsOutputCropped = DimRects.Count > 0;
+        ResolutionBadgeText = $"{quality.Label} · {quality.Width}×{quality.Height}";
+
+        OnPropertyChanged(nameof(OutputRectX));
+        OnPropertyChanged(nameof(OutputRectY));
+        OnPropertyChanged(nameof(OutputRectWidth));
+        OnPropertyChanged(nameof(OutputRectHeight));
+        OnPropertyChanged(nameof(IsOutputCropped));
+        OnPropertyChanged(nameof(ResolutionBadgeText));
     }
 
     public string BugReportText
@@ -383,6 +430,7 @@ public class MainViewModel : ViewModelBase
         AppLog.Write("MainViewModel ctor: services created");
 
         _selectedQuality = QualityOptions[0];
+        ApplyStreamQuality(_selectedQuality);
 
         _youtubeChat.MessageReceived += OnChatMessageReceived;
 
diff --git a/ViewModels/index.md b/ViewModels/index.md
index 56f106b..bd614f0 100644
--- a/ViewModels/index.md
+++ b/ViewModels/index.md
@@ -4,7 +4,7 @@ MVVM layer. See [`schema.md`](../schema.md) for the memory-map conventions.
 
 | File | Purpose |
 |------|---------|
-| `MainViewModel.cs` | The app brain: scenes/sources collections + commands, stream state (`IsLive`/`IsOffline`/`IsConnected`), chat feed, overlays, layout save/open, **resolution dropdown** (`QualityOptions`, `SelectedQuality`, `ResolutionHelp`, `ApplyStreamQuality`) |
+| `MainViewModel.cs` | The app brain: scenes/sources collections + commands, stream state (`IsLive`/`IsOffline`/`IsConnected`), chat feed, overlays, layout save/open, **resolution dropdown** (`QualityOptions`, `SelectedQuality`, `ResolutionHelp`, `ApplyStreamQuality`) that computes the output rect over the 1920×1080 master (`OutputRectX/Y/W/H`, `DimRects`, `IsOutputCropped`, `ResolutionBadgeText`) |
 | `GoLiveViewModel.cs` | Start Stream dialog: title/description/visibility, start/cancel requests |
 | `ReuseImageViewModel.cs` | Add Image dialog: candidate list (`ReuseImageCandidate`), reuse/new/cancel |
 
diff --git a/ai.md b/ai.md
index f33ec90..0745a89 100644
--- a/ai.md
+++ b/ai.md
@@ -59,7 +59,7 @@ C# / WPF (.NET 8) following MVVM:
 - Services are currently instantiated in MainViewModel's constructor — no DI container yet
 - Layout persists to SQLite (`Microsoft.Data.Sqlite`); scenes/sources/asset bytes stored in the DB, asset identity is a SHA-256 content hash (1:M reuse, no file paths — assets are always available)
 - Theming: all custom styles live in `Themes/Controls.xaml`, merged in `App.xaml` — never duplicate styles per-window (dialog duplicates were consolidated into this dictionary)
-- Resolution tiers (bottom bar): 1080p60@8 → 1080p30@8 → 720p60@6 → 480p30@2.5 Mbps; default = first. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable)
+- Resolution tiers (bottom bar): 1080p60@8 (default) → 1080p30@8 → 720p60@6 → 720p30@6 → **Vertical 1080p60@8 (9:16, 1080×1920)**. The composition master frame is **always 1920×1080** — a tier is an output rect + target resolution over that master, so source geometry is never rewritten (no rounding drift). 16:9 tiers use the full frame; the vertical tier uses a centered **607×1080** window and the preview dims the cropped side strips at 55% black with an accent outline (semi-crop — the cut area stays visible). A resolution badge in the preview corner shows the active tier; the bottom bar shows bitrate/FPS. A **tooltip** explains finding upload bandwidth — an in-app speed test was deliberately dropped (unreliable). The future encoder crops the master to the rect and scales to the tier's Width×Height
 - Crash diagnosis: `AppLog` writes startup checkpoints to `%APPDATA%\ytLlive\startup.log`; `App.xaml.cs` logs `DispatcherUnhandledException`/`AppDomain.UnhandledException`. When WPF won't run from WSL, this log is how you find the failure (it caught the `MenuItemRole.Separator` XAML crash and the ComboBox SelectionBoxItem bug)
 
 ### Current limitations / TODOs