diff --git a/crates/render/src/color.rs b/crates/render/src/color.rs
index c423665d2..158dde42f 100644
--- a/crates/render/src/color.rs
+++ b/crates/render/src/color.rs
@@ -153,6 +153,26 @@ impl Pipe {
         p
     }
 
+    /// A copy of `src` converted by `c` and quantised to the bit depth, in one pass: one read and
+    /// one write of the frame instead of a copy, a conversion and a quantise pass (a 1080p float
+    /// frame is 33 MB, and these passes are limited by memory speed). The same pixels as
+    /// [`convert`] then [`Pipe::quantize`].
+    pub fn copy_converted(&self, src: &Image, c: Option<&Conversion>) -> Image {
+        let levels = self.levels;
+        let data = src
+            .data
+            .par_iter()
+            .map(|&p| {
+                let mut p = c.map_or(p, |c| convert_px(p, c));
+                if let Some(l) = levels {
+                    quantize_px(&mut p, l, 1.0 / l);
+                }
+                p
+            })
+            .collect();
+        Image { width: src.width, height: src.height, data }
+    }
+
     /// Clamp and quantise to the bit depth (no-op in 32 bpc).
     pub fn quantize(&self, img: &mut Image) {
         self.quantize_region(img, Region::Full);
@@ -265,14 +285,18 @@ fn quantize_rect(img: &mut Image, r: PxRect, levels: f32) {
 
 /// Convert premultiplied pixels (on straight colour).
 pub fn convert(img: &mut Image, c: &Conversion) {
-    img.data.par_iter_mut().for_each(|p| {
-        let a = p[3];
-        if a <= 0.0 {
-            return;
-        }
-        let o = c.apply([p[0] / a, p[1] / a, p[2] / a]);
-        *p = [o[0] * a, o[1] * a, o[2] * a, a];
-    });
+    img.data.par_iter_mut().for_each(|p| *p = convert_px(*p, c));
+}
+
+/// [`convert`] of one pixel.
+#[inline]
+fn convert_px(p: [f32; 4], c: &Conversion) -> [f32; 4] {
+    let a = p[3];
+    if a <= 0.0 {
+        return p;
+    }
+    let o = c.apply([p[0] / a, p[1] / a, p[2] / a]);
+    [o[0] * a, o[1] * a, o[2] * a, a]
 }
 
 /// Compand: an exponential knee from 80%, approaching 1.0 (linear light, per channel).
@@ -349,6 +373,35 @@ mod tests {
         }
     }
 
+    /// The fused footage pass gives the pixels of a copy, a conversion and a quantise pass, bit
+    /// for bit, at every depth, with and without a conversion.
+    #[test]
+    fn copy_converted_is_convert_then_quantize() {
+        let mut img = Image::new(17, 5);
+        for (i, p) in img.data.iter_mut().enumerate() {
+            *p = match i % 7 {
+                0 => [0.3, -0.2, 0.71, 0.9],
+                1 => [-0.0, 0.0, 0.0, 0.0],
+                2 => [1.7, 0.4, f32::NAN, 0.5],
+                3 => [0.0; 4],
+                _ => [i as f32 / 90.0, 0.5, 0.25, 1.0],
+            };
+        }
+        for depth in [effectcraft_project::BitDepth::Bpc8, effectcraft_project::BitDepth::Bpc16, effectcraft_project::BitDepth::Bpc32] {
+            let pipe = Pipe::of(&ProjectSettings { bit_depth: depth, ..Default::default() });
+            for c in [None, Some(Conversion::linearize(ColorSpace::Srgb))] {
+                let mut want = img.clone();
+                if let Some(c) = &c {
+                    convert(&mut want, c);
+                }
+                pipe.quantize(&mut want);
+                let got = pipe.copy_converted(&img, c.as_ref());
+                let bits = |i: &Image| i.data.iter().map(|p| p.map(f32::to_bits)).collect::<Vec<_>>();
+                assert_eq!(bits(&got), bits(&want), "{depth:?} conversion {}", c.is_some());
+            }
+        }
+    }
+
     /// Both forms `round_half_up` picks between agree on everything quantising feeds it:
     /// 0..=levels, exact halves included.
     #[test]
diff --git a/crates/render/src/pipeline.rs b/crates/render/src/pipeline.rs
index 6265cb5f7..6979afc85 100644
--- a/crates/render/src/pipeline.rs
+++ b/crates/render/src/pipeline.rs
@@ -878,6 +878,12 @@ impl<'a> Renderer<'a> {
 
     /// Source pixels of a layer in layer space (before masks/effects).
     pub(crate) fn source(&self, ctx: &EvalCtx, layer: &Layer) -> Option<Buf> {
+        self.source_with(ctx, layer, false)
+    }
+
+    /// [`Renderer::source`]; with `quantized`, footage that [`Renderer::prequantized_footage`]
+    /// counts comes quantised to the project depth.
+    fn source_with(&self, ctx: &EvalCtx, layer: &Layer, quantized: bool) -> Option<Buf> {
         let s = self.opts.scale;
         match &layer.source {
             LayerSource::Solid { item } => {
@@ -910,7 +916,7 @@ impl<'a> Renderer<'a> {
                     && let Some(nc) = self.project.comp(*item)
                 {
                     let img = self.footage_frame(ctx, layer, *item, pf, lt, None)?;
-                    return Some(self.footage_buf(&img, pf, nc.width, nc.height));
+                    return Some(self.footage_buf(&img, pf, nc.width, nc.height, false));
                 }
                 // Essential Properties overrides render the nested comp with this instance's
                 // values.
@@ -959,7 +965,7 @@ impl<'a> Renderer<'a> {
                     }
                 }
                 let (img, pf) = self.footage_picture_of(ctx, layer, item, f)?;
-                Some(self.footage_buf(&img, pf, f.width, f.height))
+                Some(self.footage_buf(&img, pf, f.width, f.height, quantized && Self::prequantized_footage(layer)))
             }
             // (the font files go to this render's log, which `ctx` may not carry: see
             // [`Renderer::with_reads`])
@@ -992,15 +998,42 @@ impl<'a> Renderer<'a> {
 
     /// A decoded frame of `f` as a layer buffer covering `w`×`h` layer pixels (the footage's
     /// nominal size; proxies are scaled up to it), converted from its colour profile.
-    fn footage_buf(&self, img: &Image, f: &Footage, w: u32, h: u32) -> Buf {
-        let mut buf = match self.footage_layout(img, w, h) {
-            FootageLayout::Native { scale } => Buf { img: img.clone(), offset: [0.0; 2], scale },
-            FootageLayout::Resample { width, height, scale } => Buf { img: effectcraft_raster::resample(img, width, height), offset: [0.0; 2], scale },
-        };
-        if let Some(c) = self.pipe.media_in(f) {
-            color::convert(&mut buf.img, &c);
+    ///
+    /// `quantized`: also clamp and quantise it to the project depth, as [`Renderer::masked_source`]
+    /// would (fused with the copy of the cached frame: one pass over it instead of three).
+    fn footage_buf(&self, img: &Image, f: &Footage, w: u32, h: u32, quantized: bool) -> Buf {
+        let c = self.pipe.media_in(f);
+        match self.footage_layout(img, w, h) {
+            FootageLayout::Native { scale } => {
+                let img = match (quantized, &c) {
+                    (true, _) => self.pipe.copy_converted(img, c.as_ref()),
+                    (false, Some(c)) => {
+                        let mut img = img.clone();
+                        color::convert(&mut img, c);
+                        img
+                    }
+                    (false, None) => img.clone(),
+                };
+                Buf { img, offset: [0.0; 2], scale }
+            }
+            FootageLayout::Resample { width, height, scale } => {
+                let mut img = effectcraft_raster::resample(img, width, height);
+                if let Some(c) = &c {
+                    color::convert(&mut img, c);
+                }
+                if quantized {
+                    self.pipe.quantize(&mut img);
+                }
+                Buf { img, offset: [0.0; 2], scale }
+            }
         }
-        buf
+    }
+
+    /// The layer's source is footage that [`Renderer::source`] hands over already quantised
+    /// ([`Renderer::footage_buf`]): footage without masks (masks apply to unquantised pixels).
+    /// Collapsed layers may be vector footage, drawn elsewhere: not counted.
+    fn prequantized_footage(layer: &Layer) -> bool {
+        matches!(layer.source, LayerSource::Footage { .. }) && !layer.switches.collapse && layer.masks().is_none_or(|m| m.groups().next().is_none())
     }
 
     /// How [`Renderer::footage_buf`] lays out a decoded frame `img` of footage `w`×`h` layer
@@ -1159,13 +1192,14 @@ impl<'a> Renderer<'a> {
 
     /// Source → masks, clamped/quantised to the project depth.
     fn masked_source(&self, ctx: &EvalCtx, layer: &Layer) -> Option<Buf> {
-        let mut buf = match self.content_times(ctx, layer) {
-            Some(times) => self.blurred_source(ctx, layer, &times)?,
-            None => self.source(ctx, layer)?,
+        let (mut buf, quantized) = match self.content_times(ctx, layer) {
+            Some(times) => (self.blurred_source(ctx, layer, &times)?, false),
+            None => (self.source_with(ctx, layer, true)?, Self::prequantized_footage(layer)),
         };
-        // A solid is filled with a quantised colour: only masks can take it off the grid.
+        // A solid is filled with a quantised colour, and plain footage comes quantised: only
+        // masks can take them off the grid.
         let solid = matches!(layer.source, LayerSource::Solid { .. });
-        if masks::apply(ctx, layer, &mut buf, self.mask_blur(ctx, layer)) || !solid {
+        if masks::apply(ctx, layer, &mut buf, self.mask_blur(ctx, layer)) || !(solid || quantized) {
             self.pipe.quantize(&mut buf.img);
         }
         Some(buf)