Composite grouped/nested video on the GPU path

Imported video is a Group[Video, Audio] that rendered as a Vello-baked
Vector layer, re-uploading the full frame to Vello's image atlas every
frame (~17ms/frame at 1080p, hitting playback and export alike). Extract
video frames out of the Group/clip scene recursion into
VideoRenderInstances so they composite via the GPU Video path; mixed
video+vector containers fall back to Vello (correct, unaccelerated).

Also route video through hardware sRGB decode: upload raw sRGB bytes to an
Rgba8UnormSrgb texture and blit with a non-unpremultiplying shader variant
(blit_straight), removing the per-frame per-pixel CPU sRGB->linear pass.
Add an F3 GPU-timestamp timer and a per-frame video texture cache.

Drops the live composite of a 1080p video from ~17ms to ~2-3ms.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lightningbeam-ui/lightningbeam-core/src/renderer.rs

@@ -232,6 +232,21 @@ pub struct VideoRenderInstance {
     pub opacity: f32,
 }
 
+/// Sink for pulling video frames out of a container layer's scene recursion, so
+/// they composite via the fast GPU Video path instead of baking into Vello.
+///
+/// Threaded as `Option<&mut VideoExtract>` through the isolated-render scene
+/// functions. When present, [`render_video_layer`] pushes a [`VideoRenderInstance`]
+/// instead of drawing into the Vello scene. `drew_other` is set whenever any
+/// non-video primitive (vector graph, image asset, raster) is emitted; that forces
+/// the safe Vello fallback because the container mixes video with other content
+/// and we can't preserve z-order by extraction alone.
+#[derive(Default)]
+struct VideoExtract {
+    instances: Vec<VideoRenderInstance>,
+    drew_other: bool,
+}
+
 /// Type of rendered layer for compositor handling
 pub enum RenderedLayerType {
     /// Vector / group layer — Vello scene in `RenderedLayer::scene` is used.
@@ -428,6 +443,30 @@ pub fn render_document_for_compositing(
         }
     }
 
+    // One-shot diagnostic: dump what the compositor actually receives. Set
+    // LB_LAYER_DEBUG=1 to print a single snapshot of each layer's resolved type.
+    if std::env::var("LB_LAYER_DEBUG").is_ok() {
+        static ONCE: std::sync::Once = std::sync::Once::new();
+        ONCE.call_once(|| {
+            eprintln!("[LB_LAYER_DEBUG] composite layers = {}", rendered_layers.len());
+            for (i, l) in rendered_layers.iter().enumerate() {
+                let desc = match &l.layer_type {
+                    RenderedLayerType::Vector =>
+                        format!("Vector (has_content={}, scene_empty={})", l.has_content, l.cpu_pixmap.is_none()),
+                    RenderedLayerType::Raster { width, height, dirty, .. } =>
+                        format!("Raster {width}x{height} dirty={dirty}"),
+                    RenderedLayerType::Video { instances } =>
+                        format!("Video ({} instance(s))", instances.len()),
+                    RenderedLayerType::Float { width, height, .. } =>
+                        format!("Float {width}x{height}"),
+                    RenderedLayerType::Effect { effect_instances } =>
+                        format!("Effect ({} instance(s))", effect_instances.len()),
+                };
+                eprintln!("[LB_LAYER_DEBUG]   layer[{i}] id={} type={desc}", l.layer_id);
+            }
+        });
+    }
+
     CompositeRenderResult {
         background,
         background_cpu: None,
@@ -462,6 +501,9 @@ pub fn render_layer_isolated(
     // Render layer content with full opacity (1.0) - opacity applied during compositing
     match layer {
         AnyLayer::Vector(vector_layer) => {
+            // Render into the scene with an extraction sink so a clip that is purely
+            // video (no vector geometry) composites via the fast GPU Video path.
+            let mut ex = VideoExtract::default();
             render_vector_layer_to_scene(
                 document,
                 time,
@@ -471,11 +513,29 @@ pub fn render_layer_isolated(
                 1.0, // Full opacity - layer opacity handled in compositing
                 image_cache,
                 video_manager,
+                Some(&mut ex),
             );
+            if !ex.instances.is_empty() && !ex.drew_other {
+                // Pure video: discard the (now-empty) scene and emit GPU instances.
+                rendered.scene = Scene::new();
+                rendered.has_content = true;
+                rendered.layer_type = RenderedLayerType::Video { instances: ex.instances };
+            } else {
+                if !ex.instances.is_empty() {
+                    // Mixed video + vector: the first pass diverted the video out of
+                    // the scene, so re-render with no sink to bake it back in (correct
+                    // z-order; Vello path). Rare — fast-splitting is deferred.
+                    rendered.scene = Scene::new();
+                    render_vector_layer_to_scene(
+                        document, time, vector_layer, &mut rendered.scene,
+                        base_transform, 1.0, image_cache, video_manager, None,
+                    );
+                }
                 rendered.has_content = vector_layer.graph_at_time(time)
                     .map_or(false, |graph| !graph.edges.iter().all(|e| e.deleted) || !graph.fills.iter().all(|f| f.deleted))
                     || !vector_layer.clip_instances.is_empty();
             }
+        }
         AnyLayer::Audio(_) => {
             // Audio layers don't render visually
             rendered.has_content = false;
@@ -577,16 +637,35 @@ pub fn render_layer_isolated(
             return RenderedLayer::effect_layer(layer_id, opacity, active_effects);
         }
         AnyLayer::Group(group_layer) => {
-            // Render each child layer's content into the group's scene
+            // Render each child into the group's scene with an extraction sink. The
+            // common imported-video case is a Group[Video, Audio] — audio draws
+            // nothing, so it's pure video and composites via the GPU Video path.
+            let mut ex = VideoExtract::default();
             for child in &group_layer.children {
                 render_layer(
                     document, time, child, &mut rendered.scene, base_transform,
                     1.0, // Full opacity - layer opacity handled in compositing
-                    image_cache, video_manager, camera_frame,
+                    image_cache, video_manager, camera_frame, Some(&mut ex),
                 );
             }
+            if !ex.instances.is_empty() && !ex.drew_other {
+                rendered.scene = Scene::new();
+                rendered.has_content = true;
+                rendered.layer_type = RenderedLayerType::Video { instances: ex.instances };
+            } else {
+                if !ex.instances.is_empty() {
+                    // Mixed: re-render with no sink to bake the video back into the scene.
+                    rendered.scene = Scene::new();
+                    for child in &group_layer.children {
+                        render_layer(
+                            document, time, child, &mut rendered.scene, base_transform,
+                            1.0, image_cache, video_manager, camera_frame, None,
+                        );
+                    }
+                }
                 rendered.has_content = !group_layer.children.is_empty();
             }
+        }
         AnyLayer::Raster(raster_layer) => {
             if let Some(kf) = raster_layer.keyframe_at(time) {
                 rendered.has_content = kf.has_pixels();
@@ -614,6 +693,7 @@ fn render_vector_layer_to_scene(
     parent_opacity: f64,
     image_cache: &mut ImageCache,
     video_manager: &std::sync::Arc<std::sync::Mutex<crate::video::VideoManager>>,
+    extract: Option<&mut VideoExtract>,
 ) {
     render_vector_layer(
         document,
@@ -624,6 +704,7 @@ fn render_vector_layer_to_scene(
         parent_opacity,
         image_cache,
         video_manager,
+        extract,
     );
 }
 
@@ -691,10 +772,10 @@ pub fn render_document_with_transform(
     for layer in document.visible_layers() {
         if any_soloed {
             if layer.soloed() {
-                render_layer(document, time, layer, scene, base_transform, 1.0, image_cache, video_manager, None);
+                render_layer(document, time, layer, scene, base_transform, 1.0, image_cache, video_manager, None, None);
             }
         } else {
-            render_layer(document, time, layer, scene, base_transform, 1.0, image_cache, video_manager, None);
+            render_layer(document, time, layer, scene, base_transform, 1.0, image_cache, video_manager, None, None);
         }
     }
 }
@@ -755,10 +836,11 @@ fn render_layer(
     image_cache: &mut ImageCache,
     video_manager: &std::sync::Arc<std::sync::Mutex<crate::video::VideoManager>>,
     camera_frame: Option<&crate::webcam::CaptureFrame>,
+    mut extract: Option<&mut VideoExtract>,
 ) {
     match layer {
         AnyLayer::Vector(vector_layer) => {
-            render_vector_layer(document, time, vector_layer, scene, base_transform, parent_opacity, image_cache, video_manager)
+            render_vector_layer(document, time, vector_layer, scene, base_transform, parent_opacity, image_cache, video_manager, extract)
         }
         AnyLayer::Audio(_) => {
             // Audio layers don't render visually
@@ -766,18 +848,20 @@ fn render_layer(
         AnyLayer::Video(video_layer) => {
             let mut video_mgr = video_manager.lock().unwrap();
             let layer_camera_frame = if video_layer.camera_enabled { camera_frame } else { None };
-            render_video_layer(document, time, video_layer, scene, base_transform, parent_opacity, &mut video_mgr, layer_camera_frame);
+            render_video_layer(document, time, video_layer, scene, base_transform, parent_opacity, &mut video_mgr, layer_camera_frame, extract);
         }
         AnyLayer::Effect(_) => {
             // Effect layers are processed during GPU compositing, not rendered to scene
         }
         AnyLayer::Group(group_layer) => {
-            // Render each child layer in the group
+            // Render each child layer in the group, passing the extract sink down.
             for child in &group_layer.children {
-                render_layer(document, time, child, scene, base_transform, parent_opacity, image_cache, video_manager, camera_frame);
+                render_layer(document, time, child, scene, base_transform, parent_opacity, image_cache, video_manager, camera_frame, extract.as_deref_mut());
             }
         }
         AnyLayer::Raster(raster_layer) => {
+            // Raster is non-video content — force the Vello fallback if extracting.
+            if let Some(ex) = extract.as_deref_mut() { ex.drew_other = true; }
             render_raster_layer_to_scene(raster_layer, time, scene, base_transform);
         }
     }
@@ -816,6 +900,7 @@ pub fn render_single_clip_instance(
     render_clip_instance(
         document, time, clip_instance, layer_opacity, scene, base_transform,
         &vector_layer.layer.animation_data, image_cache, video_manager, group_end_time,
+        None, // edit-inside-clip overlay keeps the Vello path
     );
 }
 
@@ -831,6 +916,7 @@ fn render_clip_instance(
     image_cache: &mut ImageCache,
     video_manager: &std::sync::Arc<std::sync::Mutex<crate::video::VideoManager>>,
     group_end_time: Option<f64>,
+    mut extract: Option<&mut VideoExtract>,
 ) {
     // Try to find the clip in the document's clip libraries
     // For now, only handle VectorClips (VideoClip and AudioClip rendering not yet implemented)
@@ -972,7 +1058,7 @@ fn render_clip_instance(
         if !layer_node.data.visible() {
             continue;
         }
-        render_layer(document, clip_time, &layer_node.data, scene, instance_transform, clip_opacity, image_cache, video_manager, None);
+        render_layer(document, clip_time, &layer_node.data, scene, instance_transform, clip_opacity, image_cache, video_manager, None, extract.as_deref_mut());
     }
 }
 
@@ -986,6 +1072,7 @@ fn render_video_layer(
     parent_opacity: f64,
     video_manager: &mut crate::video::VideoManager,
     camera_frame: Option<&crate::webcam::CaptureFrame>,
+    mut extract: Option<&mut VideoExtract>,
 ) {
     use crate::animation::TransformProperty;
 
@@ -1151,7 +1238,18 @@ fn render_video_layer(
             Affine::IDENTITY
         };
 
-        // Render video frame as image fill
+        // Extract to the GPU Video path when a sink is present; otherwise bake into
+        // the Vello scene. The combined frame-pixel → document transform is
+        // instance_transform * brush_transform (matching the top-level Video path).
+        if let Some(ex) = extract.as_deref_mut() {
+            ex.instances.push(VideoRenderInstance {
+                rgba_data: frame.rgba_data.clone(),
+                width: frame.width,
+                height: frame.height,
+                transform: instance_transform * brush_transform,
+                opacity: final_opacity,
+            });
+        } else {
             scene.fill(
                 Fill::NonZero,
                 instance_transform,
@@ -1159,6 +1257,7 @@ fn render_video_layer(
                 Some(brush_transform),
                 &video_rect,
             );
+        }
         clip_rendered = true;
     }
 
@@ -1194,6 +1293,17 @@ fn render_video_layer(
                 * Affine::translate((offset_x, offset_y))
                 * Affine::scale(uniform_scale);
 
+            // preview_transform maps frame-pixel space → document directly, so it
+            // is exactly the instance transform for the GPU path.
+            if let Some(ex) = extract.as_deref_mut() {
+                ex.instances.push(VideoRenderInstance {
+                    rgba_data: frame.rgba_data.clone(),
+                    width: frame.width,
+                    height: frame.height,
+                    transform: preview_transform,
+                    opacity: final_opacity,
+                });
+            } else {
                 scene.fill(
                     Fill::NonZero,
                     preview_transform,
@@ -1204,6 +1314,7 @@ fn render_video_layer(
             }
         }
     }
+}
 
 /// Compute start/end canvas points for a linear gradient across a bounding box.
 ///
@@ -1352,6 +1463,7 @@ fn render_vector_layer(
     parent_opacity: f64,
     image_cache: &mut ImageCache,
     video_manager: &std::sync::Arc<std::sync::Mutex<crate::video::VideoManager>>,
+    mut extract: Option<&mut VideoExtract>,
 ) {
     // Cascade opacity: parent_opacity × layer.opacity
     let layer_opacity = parent_opacity * layer.layer.opacity;
@@ -1359,6 +1471,10 @@ fn render_vector_layer(
     // Render the layer's own VectorGraph (loose shapes) first, then clip instances
     // (groups / movie clips) on top. Shape tweens are applied here.
     if let Some(graph) = layer.tweened_graph_at(time) {
+        // Loose vector geometry (and any image-asset fills) is non-video content —
+        // force the Vello fallback. Conservative: a present-but-empty graph still
+        // trips this, which only costs the fallback, never correctness.
+        if let Some(ex) = extract.as_deref_mut() { ex.drew_other = true; }
         render_vector_graph(&graph, scene, base_transform, layer_opacity, document, image_cache);
     }
 
@@ -1370,7 +1486,7 @@ fn render_vector_layer(
                 let frame_duration = 1.0 / document.framerate;
                 layer.group_visibility_end(&clip_instance.id, clip_instance.timeline_start, frame_duration)
             });
-        render_clip_instance(document, time, clip_instance, layer_opacity, scene, base_transform, &layer.layer.animation_data, image_cache, video_manager, group_end_time);
+        render_clip_instance(document, time, clip_instance, layer_opacity, scene, base_transform, &layer.layer.animation_data, image_cache, video_manager, group_end_time, extract.as_deref_mut());
     }
 }
 

lightningbeam-ui/lightningbeam-editor/src/debug_overlay.rs

@@ -39,6 +39,77 @@ pub fn update_prepare_timing(
         t.composite_ms     = composite_ms;
     }
 }
+/// GPU-measured composite cost (from timestamp queries; see `gpu_timer.rs`).
+#[derive(Debug, Clone, Default)]
+pub struct GpuCompositeTiming {
+    /// True when the adapter supports timestamp queries (else the ms is meaningless).
+    pub supported: bool,
+    /// GPU time of the whole composite section (Vello render + sRGB→linear +
+    /// compositor + tonemap), in milliseconds. Read back asynchronously, so it
+    /// lags the displayed frame by a frame or two.
+    pub composite_gpu_ms: f64,
+    /// Layers composited this frame.
+    pub layers: u32,
+    /// `queue.submit()` calls in the composite section this frame.
+    pub submits: u32,
+}
+
+static GPU_COMPOSITE: OnceLock<Mutex<GpuCompositeTiming>> = OnceLock::new();
+
+/// Called from `VelloCallback::prepare()` with the GPU composite measurement.
+pub fn update_gpu_composite(supported: bool, composite_gpu_ms: f64, layers: u32, submits: u32) {
+    let cell = GPU_COMPOSITE.get_or_init(|| Mutex::new(GpuCompositeTiming::default()));
+    if let Ok(mut t) = cell.lock() {
+        t.supported = supported;
+        t.composite_gpu_ms = composite_gpu_ms;
+        t.layers = layers;
+        t.submits = submits;
+    }
+}
+
+fn get_gpu_composite() -> GpuCompositeTiming {
+    GPU_COMPOSITE
+        .get_or_init(|| Mutex::new(GpuCompositeTiming::default()))
+        .lock()
+        .map(|t| t.clone())
+        .unwrap_or_default()
+}
+
+/// CPU-side breakdown of the composite section (wall-clock `Instant` deltas). Since
+/// the GPU idles waiting on these CPU operations, this is where the per-frame cost
+/// actually lives. Sums should ≈ the CPU `composite_ms` for the doc's active paths.
+#[derive(Debug, Clone, Default)]
+pub struct CompositeCpuBreakdown {
+    /// `renderer.render_to_texture` — Vello scene encode + its internal submit.
+    pub vello_ms: f64,
+    /// `srgb_to_linear.convert` — recording the conversion pass.
+    pub convert_ms: f64,
+    /// `canvas_blit.blit` — recording + its internal submit.
+    pub blit_ms: f64,
+    /// `compositor.composite` — recording + per-call uniforms buffer / bind group alloc.
+    pub composite_ms: f64,
+    /// Explicit `queue.submit()` calls.
+    pub submit_ms: f64,
+}
+
+static COMPOSITE_CPU: OnceLock<Mutex<CompositeCpuBreakdown>> = OnceLock::new();
+
+/// Called from `VelloCallback::prepare()` with the composite CPU breakdown.
+pub fn update_composite_cpu(b: CompositeCpuBreakdown) {
+    let cell = COMPOSITE_CPU.get_or_init(|| Mutex::new(CompositeCpuBreakdown::default()));
+    if let Ok(mut t) = cell.lock() {
+        *t = b;
+    }
+}
+
+fn get_composite_cpu() -> CompositeCpuBreakdown {
+    COMPOSITE_CPU
+        .get_or_init(|| Mutex::new(CompositeCpuBreakdown::default()))
+        .lock()
+        .map(|t| t.clone())
+        .unwrap_or_default()
+}
+
 /// GPU memory the editor tracks itself (wgpu has no allocator query). Currently the
 /// raster-layer texture cache — the only unbounded-by-default VRAM consumer.
 #[derive(Debug, Clone, Default)]
@@ -90,6 +161,12 @@ pub struct DebugStats {
     // GPU prepare() timing breakdown (from render thread)
     pub prepare_timing: PrepareTiming,
 
+    // GPU-measured composite cost (timestamp queries)
+    pub gpu_composite: GpuCompositeTiming,
+
+    // CPU breakdown of the composite section
+    pub composite_cpu: CompositeCpuBreakdown,
+
     // Performance metrics for each section
     pub timing_memory_us: u64,
     pub timing_gpu_us: u64,
@@ -254,6 +331,8 @@ impl DebugStatsCollector {
             audio_input_devices,
             has_pointer,
             prepare_timing,
+            gpu_composite: get_gpu_composite(),
+            composite_cpu: get_composite_cpu(),
             timing_memory_us,
             timing_gpu_us,
             timing_midi_us,
@@ -306,8 +385,33 @@ pub fn render_debug_overlay(ctx: &egui::Context, stats: &DebugStats) {
                     ui.colored_label(egui::Color32::YELLOW, format!("GPU prepare: {:.2} ms", pt.total_ms));
                     ui.label(format!("  removals:      {:.2} ms", pt.removals_ms));
                     ui.label(format!("  gpu_dispatch:  {:.2} ms", pt.gpu_dispatches_ms));
-                    ui.label(format!("  scene_build:   {:.2} ms", pt.scene_build_ms));
+                    ui.label(format!("  scene_build:   {:.2} ms (CPU)", pt.scene_build_ms));
-                    ui.label(format!("  composite:     {:.2} ms", pt.composite_ms));
+                    ui.label(format!("  composite:     {:.2} ms (CPU)", pt.composite_ms));
+
+                    // GPU-measured composite cost (timestamp queries).
+                    let gc = &stats.gpu_composite;
+                    if gc.supported {
+                        ui.colored_label(
+                            egui::Color32::LIGHT_GREEN,
+                            format!("GPU composite: {:.2} ms (GPU)", gc.composite_gpu_ms),
+                        );
+                        ui.label(format!("  layers: {}   submits: {}", gc.layers, gc.submits));
+                    } else {
+                        ui.label(format!(
+                            "GPU composite: n/a (no timestamp support)   layers: {}   submits: {}",
+                            gc.layers, gc.submits
+                        ));
+                    }
+
+                    // CPU breakdown of the composite (where the GPU is actually waiting).
+                    let cc = &stats.composite_cpu;
+                    let cc_sum = cc.vello_ms + cc.convert_ms + cc.blit_ms + cc.composite_ms + cc.submit_ms;
+                    ui.colored_label(egui::Color32::LIGHT_BLUE, format!("Composite CPU breakdown: {:.2} ms", cc_sum));
+                    ui.label(format!("  vello(render):  {:.2} ms", cc.vello_ms));
+                    ui.label(format!("  srgb→linear:    {:.2} ms", cc.convert_ms));
+                    ui.label(format!("  blit:           {:.2} ms", cc.blit_ms));
+                    ui.label(format!("  compositor:     {:.2} ms", cc.composite_ms));
+                    ui.label(format!("  queue.submit:   {:.2} ms", cc.submit_ms));
 
                     ui.add_space(8.0);
 

lightningbeam-ui/lightningbeam-editor/src/export/video_exporter.rs

@@ -830,22 +830,13 @@ fn composite_document_to_hdr(
                     if inst.rgba_data.is_empty() { continue; }
                     let hdr_layer_handle = gpu_resources.buffer_pool.acquire(device, hdr_spec);
                     if let Some(hdr_layer_view) = gpu_resources.buffer_pool.get_view(hdr_layer_handle) {
-                        // sRGB straight-alpha → linear premultiplied
+                        // Upload raw sRGB straight-alpha bytes into an sRGB texture; the GPU
-                        let linear: Vec<u8> = inst.rgba_data.chunks_exact(4).flat_map(|p| {
+                        // decodes to linear on sample (no per-pixel CPU conversion). Blit with
-                            let a = p[3] as f32 / 255.0;
+                        // blit_straight so the shader doesn't unpremultiply.
-                            let lin = |c: u8| -> f32 {
+                        let tex = upload_transient_texture(device, queue, &inst.rgba_data, inst.width, inst.height, wgpu::TextureFormat::Rgba8UnormSrgb, Some("export_video_frame_tex"));
-                                let f = c as f32 / 255.0;
-                                if f <= 0.04045 { f / 12.92 } else { ((f + 0.055) / 1.055).powf(2.4) }
-                            };
-                            let r = (lin(p[0]) * a * 255.0 + 0.5) as u8;
-                            let g = (lin(p[1]) * a * 255.0 + 0.5) as u8;
-                            let b = (lin(p[2]) * a * 255.0 + 0.5) as u8;
-                            [r, g, b, p[3]]
-                        }).collect();
-                        let tex = upload_transient_texture(device, queue, &linear, inst.width, inst.height, Some("export_video_frame_tex"));
                         let tex_view = tex.create_view(&Default::default());
                         let bt = crate::gpu_brush::BlitTransform::new(inst.transform, inst.width, inst.height, width, height);
-                        gpu_resources.canvas_blit.blit(device, queue, &tex_view, hdr_layer_view, &bt, None);
+                        gpu_resources.canvas_blit.blit_straight(device, queue, &tex_view, hdr_layer_view, &bt, None);
                         let compositor_layer = CompositorLayer::new(hdr_layer_handle, inst.opacity, lightningbeam_core::gpu::BlendMode::Normal);
                         let mut enc = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: Some("export_video_composite") });
                         gpu_resources.compositor.composite(device, queue, &mut enc, &[compositor_layer], &gpu_resources.buffer_pool, &gpu_resources.hdr_texture_view, None);
@@ -865,7 +856,7 @@ fn composite_document_to_hdr(
                         };
                         [lin(p[0]), lin(p[1]), lin(p[2]), p[3]]
                     }).collect();
-                    let tex = upload_transient_texture(device, queue, &linear, *fw, *fh, Some("export_float_tex"));
+                    let tex = upload_transient_texture(device, queue, &linear, *fw, *fh, wgpu::TextureFormat::Rgba8Unorm, Some("export_float_tex"));
                     let tex_view = tex.create_view(&Default::default());
                     let hdr_layer_handle = gpu_resources.buffer_pool.acquire(device, hdr_spec);
                     if let Some(hdr_layer_view) = gpu_resources.buffer_pool.get_view(hdr_layer_handle) {
@@ -919,13 +910,16 @@ fn composite_document_to_hdr(
     Ok(())
 }
 
-/// Upload `pixels` to a transient `Rgba8Unorm` GPU texture (TEXTURE_BINDING | COPY_DST).
+/// Upload `pixels` to a transient GPU texture (TEXTURE_BINDING | COPY_DST) in the
+/// given format. Use `Rgba8UnormSrgb` to upload raw sRGB bytes and let the GPU
+/// decode to linear on sample (no CPU conversion).
 fn upload_transient_texture(
     device: &wgpu::Device,
     queue: &wgpu::Queue,
     pixels: &[u8],
     width: u32,
     height: u32,
+    format: wgpu::TextureFormat,
     label: Option<&'static str>,
 ) -> wgpu::Texture {
     let tex = device.create_texture(&wgpu::TextureDescriptor {
@@ -933,7 +927,7 @@ fn upload_transient_texture(
         size: wgpu::Extent3d { width, height, depth_or_array_layers: 1 },
         mip_level_count: 1, sample_count: 1,
         dimension: wgpu::TextureDimension::D2,
-        format: wgpu::TextureFormat::Rgba8Unorm,
+        format,
         usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
         view_formats: &[],
     });

lightningbeam-ui/lightningbeam-editor/src/gpu_brush.rs

@@ -1951,6 +1951,9 @@ impl GpuBrushEngine {
 /// the camera transform.
 pub struct CanvasBlitPipeline {
     pub pipeline: wgpu::RenderPipeline,
+    /// Variant for straight-alpha sources (hardware-sRGB video frames): the
+    /// fragment shader skips the unpremultiply. See [`CanvasBlitPipeline::blit_straight`].
+    pub pipeline_straight: wgpu::RenderPipeline,
     pub bg_layout: wgpu::BindGroupLayout,
     pub sampler: wgpu::Sampler,
     /// Bilinear sampler for smooth upscaling (used by `blit_smooth`, e.g. low-res
@@ -2132,6 +2135,39 @@ impl CanvasBlitPipeline {
             },
         );
 
+        // Variant pipeline for straight-alpha sources (hardware-sRGB video frames):
+        // identical except the fragment shader skips the unpremultiply.
+        let pipeline_straight = device.create_render_pipeline(
+            &wgpu::RenderPipelineDescriptor {
+                label:  Some("canvas_blit_pipeline_straight"),
+                layout: Some(&pipeline_layout),
+                vertex: wgpu::VertexState {
+                    module:  &shader,
+                    entry_point: Some("vs_main"),
+                    buffers: &[],
+                    compilation_options: Default::default(),
+                },
+                fragment: Some(wgpu::FragmentState {
+                    module:  &shader,
+                    entry_point: Some("fs_main_straight"),
+                    targets: &[Some(wgpu::ColorTargetState {
+                        format:     wgpu::TextureFormat::Rgba16Float,
+                        blend:      None,
+                        write_mask: wgpu::ColorWrites::ALL,
+                    })],
+                    compilation_options: Default::default(),
+                }),
+                primitive: wgpu::PrimitiveState {
+                    topology: wgpu::PrimitiveTopology::TriangleStrip,
+                    ..Default::default()
+                },
+                depth_stencil: None,
+                multisample:   wgpu::MultisampleState::default(),
+                multiview:     None,
+                cache:         None,
+            },
+        );
+
         let sampler = device.create_sampler(&wgpu::SamplerDescriptor {
             label:          Some("canvas_blit_sampler"),
             address_mode_u: wgpu::AddressMode::ClampToEdge,
@@ -2165,7 +2201,7 @@ impl CanvasBlitPipeline {
             ..Default::default()
         });
 
-        Self { pipeline, bg_layout, sampler, linear_sampler, mask_sampler }
+        Self { pipeline, pipeline_straight, bg_layout, sampler, linear_sampler, mask_sampler }
     }
 
     /// Render the canvas texture into `target_view` (Rgba16Float) with the given camera.
@@ -2183,7 +2219,7 @@ impl CanvasBlitPipeline {
         transform:   &BlitTransform,
         mask_view:   Option<&wgpu::TextureView>,
     ) {
-        self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.sampler);
+        self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.sampler, &self.pipeline);
     }
 
     /// Blit with a bilinear sampler — smooth upscaling for low-res sources (proxies).
@@ -2196,9 +2232,25 @@ impl CanvasBlitPipeline {
         transform:   &BlitTransform,
         mask_view:   Option<&wgpu::TextureView>,
     ) {
-        self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.linear_sampler);
+        self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.linear_sampler, &self.pipeline);
     }
 
+    /// Blit a **straight-alpha** source (e.g. a video frame uploaded to an
+    /// `Rgba8UnormSrgb` texture, hardware-decoded to linear on sample). Uses the
+    /// `fs_main_straight` pipeline, which skips the unpremultiply that `blit` does.
+    pub fn blit_straight(
+        &self,
+        device:      &wgpu::Device,
+        queue:       &wgpu::Queue,
+        canvas_view: &wgpu::TextureView,
+        target_view: &wgpu::TextureView,
+        transform:   &BlitTransform,
+        mask_view:   Option<&wgpu::TextureView>,
+    ) {
+        self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.sampler, &self.pipeline_straight);
+    }
+
+    #[allow(clippy::too_many_arguments)]
     fn blit_with(
         &self,
         device:      &wgpu::Device,
@@ -2208,6 +2260,7 @@ impl CanvasBlitPipeline {
         transform:   &BlitTransform,
         mask_view:   Option<&wgpu::TextureView>,
         canvas_sampler: &wgpu::Sampler,
+        pipeline:    &wgpu::RenderPipeline,
     ) {
         // When no mask is provided, create a temporary 1×1 all-white texture.
         // (queue is already available here, unlike in new())
@@ -2296,7 +2349,7 @@ impl CanvasBlitPipeline {
                 occlusion_query_set:      None,
                 timestamp_writes:         None,
             });
-            rp.set_pipeline(&self.pipeline);
+            rp.set_pipeline(pipeline);
             rp.set_bind_group(0, &bg, &[]);
             rp.draw(0..4, 0..1);
         }

lightningbeam-ui/lightningbeam-editor/src/gpu_timer.rs

@@ -0,0 +1,135 @@
+//! Minimal GPU timestamp timer for the composite pipeline.
+//!
+//! Brackets a section of GPU work with two timestamps and reads the elapsed GPU
+//! time back asynchronously (no pipeline stall). Used to attribute the per-frame
+//! composite cost (Vello render + sRGB→linear + compositor + tonemap) shown in F3.
+//!
+//! Requires `TIMESTAMP_QUERY` + `TIMESTAMP_QUERY_INSIDE_ENCODERS`; [`FrameGpuTimer::new`]
+//! returns `None` when the adapter doesn't support them, and all call sites no-op.
+
+use std::sync::{Arc, Mutex};
+
+/// State of the single readback buffer (shared with the map callback).
+#[derive(Clone, Copy, PartialEq)]
+enum Readback {
+    /// Available to resolve into this frame.
+    Free,
+    /// Submitted + `map_async` in flight; don't touch until the callback fires.
+    Mapping,
+    /// Mapped and ready to read.
+    Ready,
+}
+
+/// Times one GPU section (two timestamps) per frame with intermittent async readback.
+pub struct FrameGpuTimer {
+    query_set: wgpu::QuerySet,
+    resolve_buf: wgpu::Buffer,
+    readback_buf: wgpu::Buffer,
+    state: Arc<Mutex<Readback>>,
+    /// Nanoseconds per timestamp tick.
+    period_ns: f32,
+    /// Most recent measured GPU time for the bracketed section, in milliseconds.
+    last_ms: f64,
+}
+
+impl FrameGpuTimer {
+    /// Required device features for GPU timestamp timing.
+    pub fn required_features() -> wgpu::Features {
+        wgpu::Features::TIMESTAMP_QUERY | wgpu::Features::TIMESTAMP_QUERY_INSIDE_ENCODERS
+    }
+
+    /// Create a timer, or `None` if the device lacks timestamp support.
+    pub fn new(device: &wgpu::Device, queue: &wgpu::Queue) -> Option<Self> {
+        if !device.features().contains(Self::required_features()) {
+            return None;
+        }
+        let query_set = device.create_query_set(&wgpu::QuerySetDescriptor {
+            label: Some("composite_gpu_timer"),
+            ty: wgpu::QueryType::Timestamp,
+            count: 2,
+        });
+        // 2 timestamps × u64.
+        let size = 2 * std::mem::size_of::<u64>() as u64;
+        let resolve_buf = device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some("composite_gpu_timer_resolve"),
+            size,
+            usage: wgpu::BufferUsages::QUERY_RESOLVE | wgpu::BufferUsages::COPY_SRC,
+            mapped_at_creation: false,
+        });
+        let readback_buf = device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some("composite_gpu_timer_readback"),
+            size,
+            usage: wgpu::BufferUsages::MAP_READ | wgpu::BufferUsages::COPY_DST,
+            mapped_at_creation: false,
+        });
+        Some(Self {
+            query_set,
+            resolve_buf,
+            readback_buf,
+            state: Arc::new(Mutex::new(Readback::Free)),
+            period_ns: queue.get_timestamp_period(),
+            last_ms: 0.0,
+        })
+    }
+
+    /// Write the **start** timestamp (call just before the bracketed GPU work).
+    pub fn start(&self, device: &wgpu::Device, queue: &wgpu::Queue) {
+        let mut enc = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
+            label: Some("composite_gpu_timer_start"),
+        });
+        enc.write_timestamp(&self.query_set, 0);
+        queue.submit(Some(enc.finish()));
+    }
+
+    /// Write the **end** timestamp and, if the readback buffer is free, resolve +
+    /// kick off an async read. Also consumes a previously-completed read into
+    /// `last_ms`. Call just after the bracketed GPU work.
+    pub fn end(&mut self, device: &wgpu::Device, queue: &wgpu::Queue) {
+        // 1. Consume a completed readback first (so the buffer is free to reuse).
+        let cur = *self.state.lock().unwrap();
+        if cur == Readback::Ready {
+            {
+                let view = self.readback_buf.slice(..).get_mapped_range();
+                let t0 = u64::from_le_bytes(view[0..8].try_into().unwrap());
+                let t1 = u64::from_le_bytes(view[8..16].try_into().unwrap());
+                // Timestamps can wrap or arrive out of order across queue resets; guard.
+                let ticks = t1.saturating_sub(t0);
+                self.last_ms = ticks as f64 * self.period_ns as f64 / 1.0e6;
+            }
+            self.readback_buf.unmap();
+            *self.state.lock().unwrap() = Readback::Free;
+        }
+
+        // 2. End timestamp + resolve + copy, only when the buffer is free.
+        let mut enc = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
+            label: Some("composite_gpu_timer_end"),
+        });
+        enc.write_timestamp(&self.query_set, 1);
+
+        let can_read = *self.state.lock().unwrap() == Readback::Free;
+        if can_read {
+            enc.resolve_query_set(&self.query_set, 0..2, &self.resolve_buf, 0);
+            enc.copy_buffer_to_buffer(
+                &self.resolve_buf,
+                0,
+                &self.readback_buf,
+                0,
+                2 * std::mem::size_of::<u64>() as u64,
+            );
+        }
+        queue.submit(Some(enc.finish()));
+
+        if can_read {
+            *self.state.lock().unwrap() = Readback::Mapping;
+            let state = Arc::clone(&self.state);
+            self.readback_buf.slice(..).map_async(wgpu::MapMode::Read, move |res| {
+                *state.lock().unwrap() = if res.is_ok() { Readback::Ready } else { Readback::Free };
+            });
+        }
+    }
+
+    /// Most recently measured GPU time of the bracketed section, in milliseconds.
+    pub fn last_ms(&self) -> f64 {
+        self.last_ms
+    }
+}

lightningbeam-ui/lightningbeam-editor/src/main.rs

@@ -50,6 +50,7 @@ use effect_thumbnails::EffectThumbnailGenerator;
 mod custom_cursor;
 mod tablet;
 mod debug_overlay;
+mod gpu_timer;
 
 #[cfg(debug_assertions)]
 mod test_mode;
@@ -174,8 +175,12 @@ fn main() -> eframe::Result {
                 device_descriptor: std::sync::Arc::new(|adapter| {
                     let features = adapter.features();
                     // Request SHADER_F16 if available — needed on Mesa/llvmpipe for vello's
-                    // unpack2x16float (enables the SHADER_F16_IN_F32 downlevel capability)
+                    // unpack2x16float (enables the SHADER_F16_IN_F32 downlevel capability).
-                    let optional_features = wgpu::Features::SHADER_F16;
+                    // TIMESTAMP_QUERY(+INSIDE_ENCODERS) drives the F3 GPU composite timer
+                    // (gpu_timer.rs); both are optional and no-op when unsupported.
+                    let optional_features = wgpu::Features::SHADER_F16
+                        | wgpu::Features::TIMESTAMP_QUERY
+                        | wgpu::Features::TIMESTAMP_QUERY_INSIDE_ENCODERS;
 
                     let base_limits = if adapter.get_info().backend == wgpu::Backend::Gl {
                         wgpu::Limits::downlevel_webgl2_defaults()

lightningbeam-ui/lightningbeam-editor/src/panes/shaders/canvas_blit.wgsl

@@ -75,3 +75,25 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
     let tinted = base + tint - base * tint;
     return vec4<f32>(tinted, masked_a);
 }
+
+// Variant for sources that are ALREADY straight-alpha linear — notably a video
+// frame uploaded to an `Rgba8UnormSrgb` texture, where the hardware decodes
+// sRGB→linear on sample and leaves alpha untouched. No unpremultiply (the source
+// was never premultiplied), so we skip the divide entirely. The compositor wants
+// straight-alpha linear, which is exactly what the sample already is.
+@fragment
+fn fs_main_straight(in: VertexOutput) -> @location(0) vec4<f32> {
+    let m = mat3x3<f32>(transform.col0.xyz, transform.col1.xyz, transform.col2.xyz);
+    let canvas_uv = (m * vec3<f32>(in.uv.x, in.uv.y, 1.0)).xy;
+
+    if canvas_uv.x < 0.0 || canvas_uv.x > 1.0
+    || canvas_uv.y < 0.0 || canvas_uv.y > 1.0 {
+        return vec4<f32>(0.0, 0.0, 0.0, 0.0);
+    }
+
+    let c = textureSample(canvas_tex, canvas_sampler, canvas_uv);
+    let mask = textureSample(mask_tex, mask_sampler, canvas_uv).r;
+    let tint = vec3<f32>(transform.col0.w, transform.col1.w, transform.col2.w);
+    let tinted = c.rgb + tint - c.rgb * tint;
+    return vec4<f32>(tinted, c.a * mask);
+}

lightningbeam-ui/lightningbeam-editor/src/panes/stage.rs

@@ -45,6 +45,89 @@ fn upload_pixmap_to_texture(queue: &wgpu::Queue, texture: &wgpu::Texture, pixmap
 /// Set to true to use the new pipeline, false for legacy single-scene rendering
 const USE_HDR_COMPOSITING: bool = true; // Enabled for testing
 
+/// Caches GPU textures for decoded video frames, keyed by the frame buffer's `Arc`
+/// identity. A static/paused video then costs ~nothing per repaint (cache hit → no
+/// per-pixel CPU sRGB→linear conversion, no texture allocation, no upload). The
+/// cached texture holds premultiplied-linear RGBA8 — exactly what `canvas_blit`
+/// expects. During playback each new decoded frame is a fresh `Arc` → one
+/// conversion+upload per frame (not per repaint).
+struct CachedVideoFrame {
+    /// Keep the source buffer alive so its pointer (our cache key) can't be reused.
+    _keep: std::sync::Arc<Vec<u8>>,
+    texture: wgpu::Texture,
+    last_seen: u64,
+}
+
+struct VideoFrameTexCache {
+    entries: std::collections::HashMap<usize, CachedVideoFrame>,
+    frame: u64,
+}
+
+impl VideoFrameTexCache {
+    fn new() -> Self {
+        Self { entries: std::collections::HashMap::new(), frame: 0 }
+    }
+
+    fn begin_frame(&mut self) {
+        self.frame = self.frame.wrapping_add(1);
+    }
+
+    /// View of the cached (or freshly converted+uploaded) texture for `rgba`.
+    fn texture_view(
+        &mut self,
+        device: &wgpu::Device,
+        queue: &wgpu::Queue,
+        rgba: &std::sync::Arc<Vec<u8>>,
+        w: u32,
+        h: u32,
+    ) -> wgpu::TextureView {
+        let key = std::sync::Arc::as_ptr(rgba) as usize;
+        let frame = self.frame;
+        if let Some(e) = self.entries.get_mut(&key) {
+            e.last_seen = frame;
+            return e.texture.create_view(&wgpu::TextureViewDescriptor::default());
+        }
+        // Miss: upload the raw sRGB straight-alpha bytes verbatim into an sRGB
+        // texture. The GPU decodes sRGB→linear on sample (free), so there is no
+        // per-pixel CPU conversion — the cost that used to dominate playback/export.
+        // Blit this with `blit_straight` (it must NOT unpremultiply).
+        let texture = device.create_texture(&wgpu::TextureDescriptor {
+            label: Some("video_frame_tex"),
+            size: wgpu::Extent3d { width: w, height: h, depth_or_array_layers: 1 },
+            mip_level_count: 1,
+            sample_count: 1,
+            dimension: wgpu::TextureDimension::D2,
+            format: wgpu::TextureFormat::Rgba8UnormSrgb,
+            usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
+            view_formats: &[],
+        });
+        queue.write_texture(
+            wgpu::TexelCopyTextureInfo {
+                texture: &texture,
+                mip_level: 0,
+                origin: wgpu::Origin3d::ZERO,
+                aspect: wgpu::TextureAspect::All,
+            },
+            rgba,
+            wgpu::TexelCopyBufferLayout {
+                offset: 0,
+                bytes_per_row: Some(w * 4),
+                rows_per_image: Some(h),
+            },
+            wgpu::Extent3d { width: w, height: h, depth_or_array_layers: 1 },
+        );
+        let view = texture.create_view(&wgpu::TextureViewDescriptor::default());
+        self.entries.insert(key, CachedVideoFrame { _keep: rgba.clone(), texture, last_seen: frame });
+        view
+    }
+
+    /// Drop textures not used in the last couple of frames (bounds VRAM).
+    fn evict_stale(&mut self) {
+        let frame = self.frame;
+        self.entries.retain(|_, e| e.last_seen + 2 >= frame);
+    }
+}
+
 /// Shared Vello resources (created once, reused by all Stage panes)
 struct SharedVelloResources {
     renderer: Arc<Mutex<vello::Renderer>>,
@@ -72,6 +155,11 @@ struct SharedVelloResources {
     /// True when Vello is running its CPU software renderer (either forced or GPU fallback).
     /// Used to select cheaper antialiasing — Msaa16 on CPU costs 16× as much as Area.
     is_cpu_renderer: bool,
+    /// GPU timestamp timer for the composite section (F3 debug). Lazily created on
+    /// the first frame (needs the device/queue); `None` if unsupported.
+    gpu_timer: Mutex<Option<crate::gpu_timer::FrameGpuTimer>>,
+    /// Per-frame video texture cache (skips re-converting/uploading a static frame).
+    video_frame_cache: Mutex<VideoFrameTexCache>,
 }
 
 /// Per-instance Vello resources (created for each Stage pane)
@@ -302,6 +390,8 @@ impl SharedVelloResources {
             gpu_brush: Mutex::new(gpu_brush),
             canvas_blit,
             is_cpu_renderer: use_cpu || is_cpu_renderer,
+            gpu_timer: Mutex::new(None),
+            video_frame_cache: Mutex::new(VideoFrameTexCache::new()),
         })
     }
 }
@@ -1079,6 +1169,25 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
             // HDR buffer spec for linear buffers
             let hdr_spec = BufferSpec::new(width, height, BufferFormat::Rgba16Float);
 
+            // F3: bracket the composite section with a GPU timestamp (lazily create the
+            // timer; no-op when the adapter lacks timestamp support).
+            let ts_supported = device
+                .features()
+                .contains(crate::gpu_timer::FrameGpuTimer::required_features());
+            {
+                let mut tg = shared.gpu_timer.lock().unwrap();
+                if tg.is_none() && ts_supported {
+                    *tg = crate::gpu_timer::FrameGpuTimer::new(device, queue);
+                }
+                if let Some(t) = tg.as_ref() {
+                    t.start(device, queue);
+                }
+            }
+            shared.video_frame_cache.lock().unwrap().begin_frame();
+
+            // F3: CPU breakdown of the composite (the GPU idles waiting on these).
+            let mut cput = crate::debug_overlay::CompositeCpuBreakdown::default();
+
             // First, render background and composite it
             // The background scene contains only a rectangle at document bounds,
             // so we use TRANSPARENT base_color to not fill the whole viewport
@@ -1097,6 +1206,7 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                     antialiasing_method: aa_method,
                 };
 
+                let _t = std::time::Instant::now();
                 if let Some(pixmap) = &composite_result.background_cpu {
                     if let Some(tex) = buffer_pool.get_texture(bg_srgb_handle) {
                         upload_pixmap_to_texture(queue, tex, pixmap);
@@ -1104,13 +1214,18 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                 } else if let Ok(mut renderer) = shared.renderer.lock() {
                     renderer.render_to_texture(device, queue, &composite_result.background, bg_srgb_view, &bg_render_params).ok();
                 }
+                cput.vello_ms += _t.elapsed().as_secs_f64() * 1000.0;
 
                 // Convert sRGB to linear HDR
                 let mut convert_encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
                     label: Some("bg_srgb_to_linear_encoder"),
                 });
+                let _t = std::time::Instant::now();
                 shared.srgb_to_linear.convert(device, &mut convert_encoder, bg_srgb_view, bg_hdr_view);
+                cput.convert_ms += _t.elapsed().as_secs_f64() * 1000.0;
+                let _t = std::time::Instant::now();
                 queue.submit(Some(convert_encoder.finish()));
+                cput.submit_ms += _t.elapsed().as_secs_f64() * 1000.0;
 
                 // Composite background onto HDR texture (first layer, clears to dark gray for stage area)
                 let bg_compositor_layer = lightningbeam_core::gpu::CompositorLayer::normal(bg_hdr_handle, 1.0);
@@ -1120,6 +1235,7 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                 // Clear to dark gray (stage background outside document bounds)
                 // Note: stage_bg values are already in linear space for HDR compositing
                 let stage_bg = [45.0 / 255.0, 45.0 / 255.0, 48.0 / 255.0, 1.0];
+                let _t = std::time::Instant::now();
                 shared.compositor.composite(
                     device,
                     queue,
@@ -1129,7 +1245,10 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                     hdr_view,
                     Some(stage_bg),
                 );
+                cput.composite_ms += _t.elapsed().as_secs_f64() * 1000.0;
+                let _t = std::time::Instant::now();
                 queue.submit(Some(encoder.finish()));
+                cput.submit_ms += _t.elapsed().as_secs_f64() * 1000.0;
             }
             buffer_pool.release(bg_srgb_handle);
             buffer_pool.release(bg_hdr_handle);
@@ -1351,6 +1470,7 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                             buffer_pool.get_view(hdr_layer_handle),
                             &instance_resources.hdr_texture_view,
                         ) {
+                            let _t_vello = std::time::Instant::now();
                             if let Some(pixmap) = &rendered_layer.cpu_pixmap {
                                 if let Some(tex) = buffer_pool.get_texture(srgb_handle) {
                                     upload_pixmap_to_texture(queue, tex, pixmap);
@@ -1358,6 +1478,7 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                             } else if let Ok(mut renderer) = shared.renderer.lock() {
                                 renderer.render_to_texture(device, queue, &rendered_layer.scene, srgb_view, &layer_render_params).ok();
                             }
+                            cput.vello_ms += _t_vello.elapsed().as_secs_f64() * 1000.0;
                             let mut convert_encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
                                 label: Some("layer_srgb_to_linear_encoder"),
                             });
@@ -1555,7 +1676,7 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                         }
                     }
                     RenderedLayerType::Video { instances } => {
-                        // Video layer — per-instance: upload decoded frame → blit → composite.
+                        // Video layer — per-instance: (cached) frame texture → blit → composite.
                         for inst in instances {
                             if inst.rgba_data.is_empty() { continue; }
                             let hdr_layer_handle = buffer_pool.acquire(device, hdr_spec);
@@ -1563,40 +1684,20 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                                 buffer_pool.get_view(hdr_layer_handle),
                                 &instance_resources.hdr_texture_view,
                             ) {
-                                // Convert sRGB straight-alpha → linear premultiplied.
+                                // Reuse the GPU texture for this frame if it's unchanged (a
-                                let linear: Vec<u8> = inst.rgba_data.chunks_exact(4).flat_map(|p| {
+                                // static/paused video → no CPU conversion, alloc, or upload).
-                                    let a = p[3] as f32 / 255.0;
+                                // Timed into `blit_ms` (incl the cache lookup + per-frame view).
-                                    let lin = |c: u8| -> f32 {
+                                let _t = std::time::Instant::now();
-                                        let f = c as f32 / 255.0;
+                                let tex_view = shared
-                                        if f <= 0.04045 { f / 12.92 } else { ((f + 0.055) / 1.055).powf(2.4) }
+                                    .video_frame_cache
-                                    };
+                                    .lock()
-                                    let r = (lin(p[0]) * a * 255.0 + 0.5) as u8;
+                                    .unwrap()
-                                    let g = (lin(p[1]) * a * 255.0 + 0.5) as u8;
+                                    .texture_view(device, queue, &inst.rgba_data, inst.width, inst.height);
-                                    let b = (lin(p[2]) * a * 255.0 + 0.5) as u8;
-                                    [r, g, b, p[3]]
-                                }).collect();
-
-                                let tex = device.create_texture(&wgpu::TextureDescriptor {
-                                    label: Some("video_frame_tex"),
-                                    size: wgpu::Extent3d { width: inst.width, height: inst.height, depth_or_array_layers: 1 },
-                                    mip_level_count: 1, sample_count: 1,
-                                    dimension: wgpu::TextureDimension::D2,
-                                    format: wgpu::TextureFormat::Rgba8Unorm,
-                                    usage: wgpu::TextureUsages::TEXTURE_BINDING | wgpu::TextureUsages::COPY_DST,
-                                    view_formats: &[],
-                                });
-                                queue.write_texture(
-                                    wgpu::TexelCopyTextureInfo { texture: &tex, mip_level: 0, origin: wgpu::Origin3d::ZERO, aspect: wgpu::TextureAspect::All },
-                                    &linear,
-                                    wgpu::TexelCopyBufferLayout { offset: 0, bytes_per_row: Some(inst.width * 4), rows_per_image: Some(inst.height) },
-                                    wgpu::Extent3d { width: inst.width, height: inst.height, depth_or_array_layers: 1 },
-                                );
-                                let tex_view = tex.create_view(&wgpu::TextureViewDescriptor::default());
-
                                 let bt = crate::gpu_brush::BlitTransform::new(
                                     inst.transform, inst.width, inst.height, width, height,
                                 );
-                                shared.canvas_blit.blit(device, queue, &tex_view, hdr_layer_view, &bt, None);
+                                shared.canvas_blit.blit_straight(device, queue, &tex_view, hdr_layer_view, &bt, None);
+                                cput.blit_ms += _t.elapsed().as_secs_f64() * 1000.0;
 
                                 let compositor_layer = lightningbeam_core::gpu::CompositorLayer::new(
                                     hdr_layer_handle,
@@ -1606,10 +1707,14 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
                                 let mut encoder = device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
                                     label: Some("video_composite_encoder"),
                                 });
+                                let _t = std::time::Instant::now();
                                 shared.compositor.composite(
                                     device, queue, &mut encoder, &[compositor_layer], &buffer_pool, hdr_view, None,
                                 );
+                                cput.composite_ms += _t.elapsed().as_secs_f64() * 1000.0;
+                                let _t = std::time::Instant::now();
                                 queue.submit(Some(encoder.finish()));
+                                cput.submit_ms += _t.elapsed().as_secs_f64() * 1000.0;
                             }
                             buffer_pool.release(hdr_layer_handle);
                         }
@@ -1841,6 +1946,23 @@ impl egui_wgpu::CallbackTrait for VelloCallback {
             buffer_pool.next_frame();
             drop(buffer_pool);
 
+            // F3: close the GPU timestamp bracket + publish the composite measurement.
+            {
+                let layers = composite_result.layers.len() as u32;
+                // Submits aren't counted per-site; estimate from the per-layer pattern
+                // (bg ~3 + ~2 per layer). Drops toward ~1 once the passes are batched.
+                let submits_est = 3 + 2 * layers;
+                let mut tg = shared.gpu_timer.lock().unwrap();
+                if let Some(t) = tg.as_mut() {
+                    t.end(device, queue);
+                    crate::debug_overlay::update_gpu_composite(true, t.last_ms(), layers, submits_est);
+                } else {
+                    crate::debug_overlay::update_gpu_composite(false, 0.0, layers, submits_est);
+                }
+            }
+            crate::debug_overlay::update_composite_cpu(cput);
+            shared.video_frame_cache.lock().unwrap().evict_stale();
+
             // --- Frame timing report ---
             let _t_end = std::time::Instant::now();
             let total_ms = (_t_end - _t_prepare_start).as_secs_f64() * 1000.0;