fix(align): render at 44.1k and resample; finite guard; pre-zero tests

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

src/align/render.ts

@@ -1,9 +1,11 @@
 import * as at from "@coderline/alphatab";
 import type { Audio } from "../core/types.ts";
 import { renderMidiFile } from "../audio/render.ts";
+import { resample } from "../dsp/resample.ts";
 import type { RefTrack } from "./smf.ts";
 import type { Warp } from "./warp.ts";
 
+const RENDER_SR = 44100; // alphaSynth yields NaN at other rates (e.g. 22050), so always render here and resample
 const TPS = 1920; // division 960 at a fixed 120 bpm
 const PEAK = Math.pow(10, -1 / 20);
 const MELODIC_CHANNELS = [0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15];
@@ -17,30 +19,36 @@ export function renderMidi(
   tracks: RefTrack[], warp: Warp, sf2: Uint8Array,
   opts: { sampleRate?: number; mono?: boolean; durationSec?: number } = {},
 ): Audio {
-  const sampleRate = opts.sampleRate ?? 44100;
+  const sampleRate = opts.sampleRate ?? RENDER_SR;
   const midi = new at.midi.MidiFile();
   midi.division = 960;
   midi.addEvent(new at.midi.TempoChangeEvent(0, 500000));
   const seen = new Set<number>();
   let next = 0;
   for (const t of tracks) {
+    // Beyond 15 melodic tracks channels wrap and are shared; the first track's program wins on a shared channel.
     const ch = t.isDrums ? 9 : MELODIC_CHANNELS[next++ % MELODIC_CHANNELS.length]!;
     if (!seen.has(ch)) { seen.add(ch); midi.addEvent(new at.midi.ProgramChangeEvent(0, 0, ch, t.isDrums ? 0 : t.program)); }
     for (const n of t.notes) {
+      const offSec = warp.toAudio(n.offset);
+      if (offSec <= 0) continue;
       const on = Math.round(Math.max(0, warp.toAudio(n.onset)) * TPS);
-      const off = Math.max(on + 1, Math.round(warp.toAudio(n.offset) * TPS));
-      if (warp.toAudio(n.offset) <= 0) continue;
+      const off = Math.max(on + 1, Math.round(offSec * TPS));
       midi.addEvent(new at.midi.NoteOnEvent(0, on, ch, n.pitch, n.velocity));
       midi.addEvent(new at.midi.NoteOffEvent(0, off, ch, n.pitch, 0));
     }
   }
-  const frames = opts.durationSec === undefined ? undefined : Math.round(opts.durationSec * sampleRate);
-  const out = renderMidiFile(midi, sf2, sampleRate, { frames });
+  const out = renderMidiFile(midi, sf2, RENDER_SR, { frames: opts.durationSec === undefined ? undefined : Math.round(opts.durationSec * RENDER_SR) });
   let chans = out.channels;
+  if (sampleRate !== RENDER_SR) {
+    chans = chans.map((c) => resample(c, RENDER_SR, sampleRate));
+    if (opts.durationSec !== undefined) { const n = Math.round(opts.durationSec * sampleRate); chans = chans.map((c) => { const o = new Float32Array(n); o.set(c.subarray(0, n)); return o; }); }
+  }
   if (opts.mono) {
     const [L, R] = chans as [Float32Array, Float32Array];
     chans = [L.map((v, i) => (v + R[i]!) / 2)];
   }
+  for (const c of chans) for (let i = 0; i < c.length; i++) if (!Number.isFinite(c[i]!)) throw new Error("renderMidi: non-finite samples from synth");
   let peak = 0;
   for (const c of chans) for (let i = 0; i < c.length; i++) { const a = Math.abs(c[i]!); if (a > peak) peak = a; }
   if (peak > 0) { const g = PEAK / peak; for (const c of chans) for (let i = 0; i < c.length; i++) c[i]! *= g; }

tests/align/render.test.ts

@@ -7,7 +7,7 @@ import type { RefTrack, RefNote } from "../../src/align/smf.ts";
 const SF2 = new Uint8Array(await Bun.file("node_modules/@coderline/alphatab/dist/soundfont/sonivox.sf2").arrayBuffer());
 const note = (onset: number, offset: number, pitch: number): RefNote => ({ onset, offset, pitch, velocity: 100, channel: 0 });
 const track = (notes: RefNote[], isDrums = false): RefTrack => ({ index: 0, name: "t", program: 25, isDrums, notes });
-const SR = 44100; // alphaSynth yields NaN at 22050 Hz
+const SR = 44100;
 
 function firstAbove(x: Float32Array, thr: number): number {
   for (let i = 0; i < x.length; i++) if (Math.abs(x[i]!) > thr) return i;
@@ -49,3 +49,29 @@ test("peaks of a known sine", () => {
   expect([...q.max]).toEqual([0.5, 0]);
   expect([...q.min]).toEqual([0.25, -0.75]);
 });
+
+test("sampleRate 22050 is finite, at 22050 Hz, onset preserved", () => {
+  const a = renderMidi([track([note(1, 2, 60)])], makeWarp([{ midiSec: 0, audioSec: 0.5, kind: "manual" }]), SF2, { sampleRate: 22050, mono: true, durationSec: 4 });
+  expect(a.sampleRate).toBe(22050);
+  expect(a.channels[0]!.length).toBe(4 * 22050);
+  expect(a.channels[0]!.every(Number.isFinite)).toBe(true);
+  const t = firstAbove(a.channels[0]!, 0.02) / 22050;
+  expect(t).toBeGreaterThan(1.48);
+  expect(t).toBeLessThan(1.52);
+});
+
+test("notes before audio zero: clamped when overlapping, dropped when entirely before", () => {
+  const w = makeWarp([{ midiSec: 1, audioSec: 0, kind: "manual" }]); // audio = midi - 1
+  const dropped = renderMidi([track([note(0, 0.5, 60)]), track([note(2, 2.5, 64)])], w, SF2, { durationSec: 3 });
+  const t = firstAbove(dropped.channels[0]!, 0.02) / 44100;
+  expect(t).toBeGreaterThan(0.98);
+  const clamped = renderMidi([track([note(0.5, 2, 60)])], w, SF2, { durationSec: 3 });
+  expect(firstAbove(clamped.channels[0]!, 0.02) / 44100).toBeLessThan(0.05);
+});
+
+test("stereo with durationSec has two channels of exact length", () => {
+  const a = renderMidi([track([note(0, 0.5, 60)])], makeWarp([]), SF2, { durationSec: 2 });
+  expect(a.channels.length).toBe(2);
+  expect(a.channels[0]!.length).toBe(88200);
+  expect(a.channels[1]!.length).toBe(88200);
+});