feat: synthesize trajectory analysis windows

packages/acoustics-core/trajectory.js

@@ -74,13 +74,73 @@ export function sampleQuasiStaticWindow(scene, startTime, endTime) {
   if (Number.isFinite(scene?.duration) && endTime > scene.duration) {
     throw new RangeError("window endTime must not exceed scene.duration.");
   }
-  const sampleTime = startTime + (endTime - startTime) / 2;
+  const sampleRate = scene?.sampleRate;
+  if (!Number.isInteger(sampleRate) || sampleRate <= 0) {
+    const sampleTime = startTime + (endTime - startTime) / 2;
+    return {
+      startTime,
+      endTime,
+      sampleTime,
+      duration: endTime - startTime,
+      scene: sceneAtTime(scene, sampleTime),
+    };
+  }
+
+  // Ceil selects the first sample whose timestamp is inside each half-open
+  // boundary. Adjacent windows therefore share an exact boundary without a
+  // duplicated or omitted sample, even when their requested times are not
+  // integer multiples of the sample period.
+  const startSample = Math.ceil(startTime * sampleRate);
+  const endSample = Math.ceil(endTime * sampleRate);
+  if (endSample <= startSample) {
+    throw new RangeError("window must contain at least one sample.");
+  }
+  const alignedStartTime = startSample / sampleRate;
+  const alignedEndTime = endSample / sampleRate;
+  const sampleTime = (startSample + endSample) / (2 * sampleRate);
+  const sources = [];
+  const sourceOffsets = [];
+
+  for (const source of scene.sources) {
+    const signalStartTime = source.startTime ?? 0;
+    const signalDuration = source.duration ?? scene.duration;
+    const signalStartSample = Math.ceil(signalStartTime * sampleRate);
+    const signalEndSample = Math.ceil((signalStartTime + signalDuration) * sampleRate);
+    const activeStartSample = Math.max(startSample, signalStartSample);
+    const activeEndSample = Math.min(endSample, signalEndSample);
+    if (activeEndSample <= activeStartSample) continue;
+
+    sources.push({
+      ...source,
+      position: sourcePositionAtTime(source, sampleTime),
+      startTime: (activeStartSample - startSample) / sampleRate,
+      duration: (activeEndSample - activeStartSample) / sampleRate,
+    });
+    sourceOffsets.push({ signalStartTime, signalStartSample });
+  }
+
+  const ambient = Array.isArray(scene.ambient) ? scene.ambient.slice() : scene.ambient;
+  const signalOffsets = {
+    sceneSampleOffset: startSample,
+    sources: sourceOffsets,
+    ambient: (scene.ambient ?? []).map(() => ({ signalStartTime: 0, signalStartSample: 0 })),
+  };
+  const duration = (endSample - startSample) / sampleRate;
   return {
-    startTime,
-    endTime,
+    startTime: alignedStartTime,
+    endTime: alignedEndTime,
     sampleTime,
-    duration: endTime - startTime,
-    scene: sceneAtTime(scene, sampleTime),
+    startSample,
+    endSample,
+    sampleCount: endSample - startSample,
+    duration,
+    signalOffsets,
+    scene: {
+      ...scene,
+      duration,
+      sources,
+      ...(Array.isArray(scene.ambient) ? { ambient } : {}),
+    },
   };
 }