M11.2: audio playback + waveforms + audio effects

- Audio effects (Backwards, Bass & Treble, Delay, Flange & Chorus,
  High-Low Pass, Modulator, Parametric EQ, Reverb, Stereo Mixer, Tone)
  applied per layer in the comp mixdown, so export and preview share them.
  RBJ-cookbook biquads, Schroeder/Moorer reverb, modulated delay lines;
  stateless per block via pre-roll. Tone makes any layer audible.
- Real-time audio preview: ui-egui AudioFeed/AudioPlayback (feeder thread
  mixing ahead) behind an AudioDevice hook; the desktop app implements it
  with cpal (L6). Audio clock drives playback (consumed frames minus device
  latency, looped through the work area). Preview panel Include Audio /
  playback.muteAudio.
- Audio panel VU meters with peak hold and clip indicators; selected
  layer's Audio Levels.
- Timeline Audio > Waveform for footage with audio (L reveals Audio
  Levels, LL the Waveform), drawn from a cached per-item peak summary.
- ui.playback reports audio state and meter levels.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/render/src/audio.rs

@@ -1,10 +1,20 @@
-//! Audio mixdown of a composition: every audible footage layer (and, recursively, precomp layer)
-//! summed with its Audio Levels (dB, per channel), respecting in/out points, the Audio switch and
-//! solo. Levels are evaluated once per call (callers mix in short blocks, e.g. one video frame).
+//! Audio mixdown of a composition: every audible layer (footage with audio, precomps, and any
+//! layer with a sound-generating effect such as Tone) summed with its Audio Levels (dB, per
+//! channel), respecting in/out points, the Audio switch and solo. Layer audio effects
+//! (Effect > Audio, see [`effectcraft_effects::audio_fx`]) run on each layer's audio before
+//! its levels; Backwards plays the layer's [in, out) span reversed.
+//!
+//! Callers mix in short blocks (one video frame, or an audio device buffer). Effects and levels
+//! are evaluated once per block. To make the result independent of block boundaries, layer
+//! effects are run from a cleared state over a pre-roll of earlier audio and only the block's
+//! tail is kept — so preview playback and export produce identical samples.
+//!
 //! Time-stretched layers are resampled nearest-sample; reversed (negative stretch) layers are
 //! silent for now.
 
-use effectcraft_project::{Comp, ItemId, ItemKind, Layer, LayerSource, Project};
+use effectcraft_effects::Params;
+use effectcraft_effects::audio_fx;
+use effectcraft_project::{Comp, GroupKind, ItemId, ItemKind, Layer, LayerSource, Node, Project};
 use effectcraft_time::{TICKS_PER_SECOND, Tick};
 
 use crate::{EvalCtx, ExprHost, FootageSource};
@@ -19,32 +29,49 @@ pub fn mix_comp(project: &Project, footage: &dyn FootageSource, expr: Option<&dy
     out
 }
 
-/// Whether the comp has anything audible (footage with audio, or a precomp that has).
+/// Whether the comp has anything audible (footage with audio, a sound generator, or a precomp
+/// that has).
 pub fn comp_has_audio(project: &Project, comp: ItemId) -> bool {
     fn walk(project: &Project, comp: ItemId, depth: usize) -> bool {
         let Some(c) = project.comp(comp) else { return false };
         depth < MAX_DEPTH
             && c.layers.iter().any(|l| {
                 l.switches.audio
-                    && match &l.source {
-                        LayerSource::Footage { item } => {
-                            matches!(project.item(*item).map(|i| &i.kind), Some(ItemKind::Footage(f)) if f.has_audio && !f.missing)
-                        }
-                        LayerSource::Comp { item } => walk(project, *item, depth + 1),
-                        _ => false,
-                    }
+                    && (generates(l)
+                        || match &l.source {
+                            LayerSource::Footage { item } => {
+                                matches!(project.item(*item).map(|i| &i.kind), Some(ItemKind::Footage(f)) if f.has_audio && !f.missing)
+                            }
+                            LayerSource::Comp { item } => walk(project, *item, depth + 1),
+                            _ => false,
+                        })
             })
     }
     walk(project, comp, 0)
 }
 
-fn audible(project: &Project, l: &Layer) -> bool {
+/// Enabled audio effects of a layer (in stack order) with their effect ids.
+fn audio_effect_groups(l: &Layer) -> impl Iterator<Item = (&str, &effectcraft_project::PropGroup)> {
+    l.effects().filter(|_| l.switches.effects).into_iter().flat_map(|fx| fx.groups()).filter(|g| g.enabled).filter_map(|g| match &g.kind {
+        GroupKind::Effect { effect } if audio_fx::is_audio_effect(effect) => Some((effect.as_str(), g)),
+        _ => None,
+    })
+}
+
+/// The layer makes sound on its own (Tone).
+fn generates(l: &Layer) -> bool {
+    audio_effect_groups(l).any(|(id, _)| audio_fx::generates_audio(id))
+}
+
+/// Does the layer contribute to the mix (Audio switch on and something to hear)?
+pub fn audible(project: &Project, l: &Layer) -> bool {
     l.switches.audio
-        && match &l.source {
-            LayerSource::Footage { item } => matches!(project.item(*item).map(|i| &i.kind), Some(ItemKind::Footage(f)) if f.has_audio),
-            LayerSource::Comp { .. } => true,
-            _ => false,
-        }
+        && (generates(l)
+            || match &l.source {
+                LayerSource::Footage { item } => matches!(project.item(*item).map(|i| &i.kind), Some(ItemKind::Footage(f)) if f.has_audio),
+                LayerSource::Comp { .. } => true,
+                _ => false,
+            })
 }
 
 fn db_to_gain(db: f64) -> f32 {
@@ -61,6 +88,116 @@ fn sample_tick(i: i64, rate: u32) -> Tick {
     Tick(((i as i128 * TICKS_PER_SECOND as i128) / rate as i128) as i64)
 }
 
+struct MixEnv<'a> {
+    project: &'a Project,
+    footage: &'a dyn FootageSource,
+    expr: Option<&'a dyn ExprHost>,
+    comp_id: ItemId,
+    comp: &'a Comp,
+    rate: u32,
+    depth: usize,
+}
+
+impl MixEnv<'_> {
+    fn ctx(&self, t: Tick) -> EvalCtx<'_> {
+        let mut ctx = EvalCtx::new(self.project, self.comp_id, self.comp, t);
+        ctx.expr = self.expr;
+        ctx
+    }
+
+    /// The layer's own (pre-effect) audio for comp sample indices `i0 .. i0 + n`, silent
+    /// outside its [in, out) span. Comp sample index `k` maps to `in + out − 1 − k` when
+    /// `reversed`.
+    fn layer_raw(&self, l: &Layer, i0: i64, n: usize, reversed: bool) -> Vec<f32> {
+        let rate = self.rate;
+        let mut out = vec![0.0f32; n * 2];
+        let (in_i, out_i) = (units_ceil(l.in_point, rate), units_ceil(l.out_point, rate));
+        if reversed {
+            // Mirror the clipped range, fetch it forwards, reverse.
+            let a = i0.max(in_i);
+            let b = (i0 + n as i64).min(out_i);
+            if a >= b {
+                return out;
+            }
+            let (ma, mb) = (in_i + out_i - b, in_i + out_i - a);
+            let fwd = self.layer_raw(l, ma, (mb - ma) as usize, false);
+            for k in a..b {
+                let j = (in_i + out_i - 1 - k - ma) as usize;
+                let o = (k - i0) as usize;
+                out[o * 2] = fwd[j * 2];
+                out[o * 2 + 1] = fwd[j * 2 + 1];
+            }
+            return out;
+        }
+        let a = (in_i - i0).clamp(0, n as i64) as usize;
+        let b = (out_i - i0).clamp(0, n as i64) as usize;
+        if a >= b {
+            return out;
+        }
+        let m = b - a;
+        let speed = 100.0 / l.stretch;
+        let src_n = ((m as f64 * speed).ceil() as usize).max(1);
+        let lt = l.layer_time(sample_tick(i0 + a as i64, rate));
+        let buf = match &l.source {
+            LayerSource::Footage { item } => match self.project.item(*item).map(|i| &i.kind) {
+                Some(ItemKind::Footage(f)) if f.has_audio => self.footage.audio(*item, f, lt, src_n, rate).unwrap_or_else(|| vec![0.0; src_n * 2]),
+                _ => return out,
+            },
+            LayerSource::Comp { item } => {
+                if self.project.comp_contains(*item, self.comp_id) {
+                    return out;
+                }
+                let mut sub = vec![0.0f32; src_n * 2];
+                mix_into(self.project, self.footage, self.expr, *item, lt, rate, &mut sub, 1.0, 1.0, self.depth + 1);
+                sub
+            }
+            _ => return out,
+        };
+        let same = (speed - 1.0).abs() < 1e-9;
+        for i in 0..m {
+            let j = if same { i } else { ((i as f64 * speed) as usize).min(src_n - 1) };
+            if j * 2 + 1 >= buf.len() {
+                break;
+            }
+            out[(a + i) * 2] = buf[j * 2];
+            out[(a + i) * 2 + 1] = buf[j * 2 + 1];
+        }
+        out
+    }
+
+    /// Effect parameters at comp time `t`.
+    fn params(&self, l: &Layer, g: &effectcraft_project::PropGroup, t: Tick) -> Params {
+        let ctx = self.ctx(t);
+        let mut p = Params::default();
+        for c in &g.children {
+            if let Node::Prop(pr) = c {
+                p.values.insert(pr.match_id.clone(), ctx.value(l, pr));
+            }
+        }
+        p
+    }
+
+    /// The layer's processed audio (effects applied, levels not) for comp sample indices
+    /// `i0 .. i0 + n`.
+    fn layer_audio(&self, l: &Layer, i0: i64, n: usize) -> Vec<f32> {
+        let t = sample_tick(i0, self.rate);
+        let fx: Vec<(&str, Params)> = audio_effect_groups(l).map(|(id, g)| (id, self.params(l, g, t))).collect();
+        if fx.is_empty() {
+            return self.layer_raw(l, i0, n, false);
+        }
+        let reversed = fx.iter().any(|(id, _)| audio_fx::reverses(id));
+        let pre_s: f64 = fx.iter().map(|(id, p)| audio_fx::preroll(id, p)).sum();
+        let pre = (pre_s * self.rate as f64).ceil() as usize;
+        let mut buf = self.layer_raw(l, i0 - pre as i64, n + pre, reversed);
+        let start = l.layer_time(sample_tick(i0 - pre as i64, self.rate)).seconds();
+        for (id, p) in &fx {
+            audio_fx::process(id, p, &mut buf, self.rate, start);
+        }
+        buf.drain(..pre * 2);
+        buf
+    }
+}
+
 #[allow(clippy::too_many_arguments)]
 fn mix_into(
     project: &Project,
@@ -78,6 +215,7 @@ fn mix_into(
     if depth >= MAX_DEPTH || rate == 0 {
         return;
     }
+    let env = MixEnv { project, footage, expr, comp_id, comp, rate, depth };
     let frames = out.len() / 2;
     let any_solo = comp.layers.iter().any(|l| l.switches.solo && audible(project, l));
     let s0 = start.to_units_floor(rate as i64);
@@ -92,50 +230,64 @@ fn mix_into(
             continue;
         }
         let t_a = sample_tick(s0 + a as i64, rate);
-        let (ll, lr) = levels(project, comp_id, comp, l, t_a, expr);
+        let (ll, lr) = levels(&env, l, t_a);
         let (ll, lr) = (ll * gl, lr * gr);
         if ll == 0.0 && lr == 0.0 {
             continue;
         }
-        let n = b - a;
-        let speed = 100.0 / l.stretch;
-        let src_n = ((n as f64 * speed).ceil() as usize).max(1);
-        let lt = l.layer_time(t_a);
-        let buf = match &l.source {
-            LayerSource::Footage { item } => match project.item(*item).map(|i| &i.kind) {
-                Some(ItemKind::Footage(f)) => footage.audio(*item, f, lt, src_n, rate).unwrap_or_else(|| vec![0.0; src_n * 2]),
-                _ => continue,
-            },
-            LayerSource::Comp { item } => {
-                if project.comp_contains(*item, comp_id) {
-                    continue;
-                }
-                let mut sub = vec![0.0f32; src_n * 2];
-                mix_into(project, footage, expr, *item, lt, rate, &mut sub, 1.0, 1.0, depth + 1);
-                sub
-            }
-            _ => continue,
-        };
-        let same = (speed - 1.0).abs() < 1e-9;
-        for i in 0..n {
-            let j = if same { i } else { ((i as f64 * speed) as usize).min(src_n - 1) };
-            if j * 2 + 1 >= buf.len() {
-                break;
-            }
-            out[(a + i) * 2] += buf[j * 2] * ll;
-            out[(a + i) * 2 + 1] += buf[j * 2 + 1] * lr;
+        let buf = env.layer_audio(l, s0 + a as i64, b - a);
+        for (i, f) in buf.chunks_exact(2).enumerate() {
+            out[(a + i) * 2] += f[0] * ll;
+            out[(a + i) * 2 + 1] += f[1] * lr;
         }
     }
 }
 
-fn levels(project: &Project, comp_id: ItemId, comp: &Comp, l: &Layer, t: Tick, expr: Option<&dyn ExprHost>) -> (f32, f32) {
+fn levels(env: &MixEnv, l: &Layer, t: Tick) -> (f32, f32) {
     let Some(g) = l.props.sub("audio") else { return (1.0, 1.0) };
-    let mut ctx = EvalCtx::new(project, comp_id, comp, t);
-    ctx.expr = expr;
-    let [a, b] = ctx.v2(l, g, "levels", [0.0, 0.0]);
+    let [a, b] = env.ctx(t).v2(l, g, "levels", [0.0, 0.0]);
     (db_to_gain(a), db_to_gain(b))
 }
 
+/// A min/max peak summary of interleaved stereo audio for waveform drawing: one entry per
+/// `bin` sample frames, `[min L, max L, min R, max R]`.
+pub fn peak_summary(samples: &[f32], bin: usize) -> Vec<[f32; 4]> {
+    let bin = bin.max(1);
+    samples
+        .chunks(bin * 2)
+        .map(|c| {
+            let mut s = [f32::MAX, f32::MIN, f32::MAX, f32::MIN];
+            for f in c.chunks_exact(2) {
+                s[0] = s[0].min(f[0]);
+                s[1] = s[1].max(f[0]);
+                s[2] = s[2].min(f[1]);
+                s[3] = s[3].max(f[1]);
+            }
+            if s[0] > s[1] { [0.0; 4] } else { s }
+        })
+        .collect()
+}
+
+/// Peak summary of a footage item's audio from source time 0 over `duration`, `bins_per_sec`
+/// entries per second (rendered at a low internal rate, fetched in one-second chunks).
+pub fn footage_peaks(footage: &dyn FootageSource, item: ItemId, f: &effectcraft_project::Footage, duration: Tick, bins_per_sec: u32) -> Vec<[f32; 4]> {
+    let bins_per_sec = bins_per_sec.max(1);
+    // Enough samples per bin to catch peaks of audible content, without decoding at full rate.
+    let bin = (64usize).max(4000 / bins_per_sec as usize);
+    let rate = bin as u32 * bins_per_sec;
+    let chunk = bin * bins_per_sec as usize;
+    let total = units_ceil(duration, rate).max(0) as usize;
+    let mut out = Vec::with_capacity(total / bin + 1);
+    let mut i = 0usize;
+    while i < total {
+        let n = chunk.min(total - i);
+        let buf = footage.audio(item, f, sample_tick(i as i64, rate), n, rate).unwrap_or_else(|| vec![0.0; n * 2]);
+        out.extend(peak_summary(&buf, bin));
+        i += n;
+    }
+    out
+}
+
 #[cfg(test)]
 mod tests {
     use std::sync::Arc;