feat: edit moving source trajectories

apps/dataset-builder/README.md

@@ -20,8 +20,12 @@
    - `Tone`: 주파수와 위상을 갖는 합성 정현파
    - `Noise`: seed로 재현되는 white 또는 pink noise
    - `Audio asset`: 선택한 파일의 channel을 사용하며 짧은 파일은 반복 가능
-6. 필요하면 ambient 종류와 gain을 설정합니다.
-7. 검증 카드가 **저장 가능한 장면**이면 **Scene JSON 저장**을 누릅니다.
+6. 움직이는 음원은 **시간에 따라 음원 이동**을 켭니다. 현재 위치에서 시작해 Scene 끝까지 이어지는
+   기본 두 점 경로가 생성됩니다. 경로점의 절대 시간과 x/y/z를 수정하거나 점을 추가·삭제할 수 있습니다.
+7. **경로 미리보기** slider로 시간별 위치를 확인합니다. 번호를 눌러 경로점을 선택한 뒤 canvas를
+   클릭하면 선택한 점의 x/y가 바뀝니다. 첫 경로점은 고정 장면 호환용 `source.position`에도 동기화됩니다.
+8. 필요하면 ambient 종류와 gain을 설정합니다.
+9. 검증 카드가 **저장 가능한 장면**이면 **Scene JSON 저장**을 누릅니다.
 
 오디오 파일은 PCM WAV가 가장 안정적입니다. MP3, FLAC, OGG, M4A 등의 실제 decode 지원 여부는
 브라우저와 운영체제 codec에 따라 달라지며, 지원하지 않는 파일은 미리 듣기 시 오류로 표시됩니다.
@@ -69,3 +73,7 @@ id, 종류, 파일명과 SHA-256이 들어갑니다.
 Builder의 mix는 재현 가능한 source recipe와 위치 ground truth를 만드는 단계입니다. 자유음장 전파,
 마이크 calibration과 DAS는 Acoustic Camera에서 수행합니다. 실제 방의 반사·잔향·차폐를 Builder가
 추정하지 않습니다.
+
+이동 경로는 Scene 시작 기준의 keyframe을 직선 보간합니다. Builder의 mono 미리 듣기는 공간 위치를
+소리로 표현하지 않으므로, 움직임은 canvas에서 확인하고 실제 시간창별 위치 추정은 Acoustic Camera에서
+실행합니다. 경로점 사이의 Doppler 효과나 연속적인 전파 시간 변화는 현재 모델 범위에 포함되지 않습니다.

apps/dataset-builder/canvas-view.js

@@ -1,4 +1,5 @@
 import { SOURCE_COLORS } from "./model.js";
+import { sourcePositionAtTime } from "/packages/acoustics-core/trajectory.js";
 
 function finitePlane(plane) {
   return [plane.xMin, plane.xMax, plane.yMin, plane.yMax].every(Number.isFinite) &&
@@ -45,9 +46,50 @@ function drawGrid(context, width, height, plane) {
   context.textAlign = "left";
 }
 
-function drawSource(context, source, index, selected, plane, width, height) {
-  if (!source.position?.every(Number.isFinite)) return;
-  const point = coordinateToPixel(source.position, plane, width, height);
+function drawTrajectory(context, source, index, selected, selectedKeyframeIndex, plane, width, height) {
+  if (!Array.isArray(source.trajectory) || source.trajectory.length < 2) return;
+  const points = source.trajectory.map(({ position }) => coordinateToPixel(position, plane, width, height));
+  const color = SOURCE_COLORS[index % SOURCE_COLORS.length];
+  context.save();
+  context.strokeStyle = color;
+  context.globalAlpha = selected ? 0.85 : 0.28;
+  context.lineWidth = selected ? 2.5 : 1.5;
+  context.setLineDash([7, 5]);
+  context.beginPath();
+  points.forEach((point, pointIndex) => {
+    if (pointIndex === 0) context.moveTo(point.x, point.y);
+    else context.lineTo(point.x, point.y);
+  });
+  context.stroke();
+  context.setLineDash([]);
+  points.forEach((point, pointIndex) => {
+    context.globalAlpha = selected ? 1 : 0.42;
+    context.fillStyle = color;
+    context.beginPath();
+    context.arc(point.x, point.y, pointIndex === selectedKeyframeIndex && selected ? 6 : 4, 0, Math.PI * 2);
+    context.fill();
+    if (pointIndex === selectedKeyframeIndex && selected) {
+      context.strokeStyle = "#fff";
+      context.lineWidth = 2;
+      context.beginPath();
+      context.arc(point.x, point.y, 9, 0, Math.PI * 2);
+      context.stroke();
+    }
+  });
+  context.restore();
+}
+
+function positionAtPreviewTime(source, previewTime) {
+  try {
+    return sourcePositionAtTime(source, previewTime);
+  } catch {
+    return source.position;
+  }
+}
+
+function drawSource(context, source, position, index, selected, plane, width, height) {
+  if (!position?.every(Number.isFinite)) return;
+  const point = coordinateToPixel(position, plane, width, height);
   if (point.x < -30 || point.x > width + 30 || point.y < -30 || point.y > height + 30) return;
   const color = SOURCE_COLORS[index % SOURCE_COLORS.length];
   context.save();
@@ -81,8 +123,8 @@ export function createSceneCanvas(canvas, emptyElement, badgeElement, onMove) {
   const context = canvas.getContext("2d");
   let current = null;
 
-  function render(scene, image, plane, selectedSourceId) {
-    current = { scene, image, plane, selectedSourceId };
+  function render(scene, image, plane, selectedSourceId, previewTime = 0, selectedKeyframeIndex = 0) {
+    current = { scene, image, plane, selectedSourceId, previewTime, selectedKeyframeIndex };
     const rect = canvas.getBoundingClientRect();
     const width = Math.max(1, rect.width);
     const height = Math.max(1, rect.height);
@@ -111,12 +153,22 @@ export function createSceneCanvas(canvas, emptyElement, badgeElement, onMove) {
       context.fillRect(0, 0, width, height);
     }
     scene.sources.forEach((source, index) => {
-      drawSource(context, source, index, source.id === selectedSourceId, plane, width, height);
+      drawTrajectory(
+        context, source, index, source.id === selectedSourceId,
+        source.id === selectedSourceId ? selectedKeyframeIndex : -1,
+        plane, width, height,
+      );
+    });
+    scene.sources.forEach((source, index) => {
+      drawSource(
+        context, source, positionAtPreviewTime(source, previewTime), index,
+        source.id === selectedSourceId, plane, width, height,
+      );
     });
     emptyElement.classList.toggle("is-hidden", Boolean(image));
     badgeElement.textContent =
       `x ${plane.xMin.toFixed(2)}…${plane.xMax.toFixed(2)} m · ` +
-      `y ${plane.yMin.toFixed(2)}…${plane.yMax.toFixed(2)} m`;
+      `y ${plane.yMin.toFixed(2)}…${plane.yMax.toFixed(2)} m · t ${previewTime.toFixed(2)} s`;
   }
 
   canvas.addEventListener("pointerdown", (event) => {
@@ -128,7 +180,10 @@ export function createSceneCanvas(canvas, emptyElement, badgeElement, onMove) {
   });
 
   new ResizeObserver(() => {
-    if (current) render(current.scene, current.image, current.plane, current.selectedSourceId);
+    if (current) render(
+      current.scene, current.image, current.plane, current.selectedSourceId,
+      current.previewTime, current.selectedKeyframeIndex,
+    );
   }).observe(canvas);
 
   return { render };

apps/dataset-builder/index.html

@@ -133,6 +133,19 @@
                 <label class="field"><span>시작 (s)</span><input id="source-start" type="number" min="0" step="0.01" /></label>
                 <label class="field"><span>길이 (s)</span><input id="source-duration" type="number" min="0.01" step="0.01" /></label>
               </div>
+              <section class="trajectory-editor" aria-label="음원 이동 경로">
+                <label class="check-field trajectory-toggle"><input id="source-motion" type="checkbox" /><span>시간에 따라 음원 이동</span></label>
+                <p class="section-note">경로 시간은 Scene 시작 기준입니다. 이동을 켜면 현재 위치에서 시작해 Scene 끝까지 이어지는 두 점 경로가 만들어집니다.</p>
+                <div id="trajectory-fields" class="is-hidden">
+                  <label class="field field--wide trajectory-preview">
+                    <span>경로 미리보기 · <output id="preview-time-value" for="preview-time">0.00 s</output></span>
+                    <input id="preview-time" type="range" min="0" max="1" step="0.01" value="0" />
+                  </label>
+                  <p class="section-note">경로점을 선택하면 canvas 클릭으로 그 점의 x/y를 옮길 수 있습니다. 흰 테두리 점은 현재 선택한 경로점입니다.</p>
+                  <div class="trajectory-list" id="trajectory-list"></div>
+                  <button class="button button--ghost button--full" id="add-keyframe-button" type="button">+ 경로점 추가</button>
+                </div>
+              </section>
               <label class="field field--wide"><span>신호 종류</span><select id="source-type"><option value="tone">Tone</option><option value="noise">Noise</option><option value="asset">Audio asset</option></select></label>
               <div id="tone-fields"><label class="field field--wide"><span>주파수 (Hz)</span><input id="tone-frequency" type="number" min="1" step="1" /></label></div>
               <div id="noise-fields"><label class="field field--wide"><span>Noise color</span><select id="noise-color"><option value="white">White</option><option value="pink">Pink</option></select></label></div>

apps/dataset-builder/main.js

@@ -6,17 +6,26 @@ import { createAudioRuntime } from "./audio-runtime.js";
 import { createSceneCanvas } from "./canvas-view.js";
 import {
   DEFAULT_VIEW_PLANE,
+  MAX_TRAJECTORY_KEYFRAMES,
   SOURCE_COLORS,
   assetDescriptorForFile,
   changeSignalType,
   createSceneId,
   createSource,
   describeSignal,
+  disableSourceTrajectory,
+  enableSourceTrajectory,
+  insertTrajectoryKeyframe,
   isAssetReferenced,
   matchAssetDescriptor,
   prepareSceneForEditing,
+  removeTrajectoryKeyframe,
   referencedAssetIds,
   safeDownloadStem,
+  scaleSceneTrajectories,
+  synchronizeSourcePosition,
+  trajectoryTimeBounds,
+  updateTrajectoryKeyframeTime,
 } from "./model.js";
 
 const byId = (id) => {
@@ -34,6 +43,7 @@ const elements = Object.fromEntries(
     "plane-z", "no-source-message", "source-fields", "source-name", "source-x", "source-y", "source-z",
     "source-gain", "source-start", "source-duration", "source-type", "tone-fields", "tone-frequency",
     "noise-fields", "noise-color", "asset-fields", "source-asset", "source-channel", "source-loop",
+    "source-motion", "trajectory-fields", "trajectory-list", "preview-time", "preview-time-value", "add-keyframe-button",
     "remove-source-button", "ambient-type", "ambient-asset-field", "ambient-asset-options", "ambient-asset",
     "ambient-channel", "ambient-loop", "ambient-gain",
     "validation-dot", "validation-title", "validation-message", "save-state",
@@ -44,6 +54,8 @@ elements.validationCard = document.querySelector(".validation-card");
 const state = {
   scene: null,
   selectedSourceId: null,
+  selectedKeyframeIndex: 0,
+  previewTime: 0,
   viewPlane: { ...DEFAULT_VIEW_PLANE },
   imageElement: null,
   imageUrl: null,
@@ -70,8 +82,10 @@ const canvasView = createSceneCanvas(
   ({ x, y }) => {
     const source = selectedSource();
     if (!source) return;
-    source.position[0] = Number(x.toFixed(4));
-    source.position[1] = Number(y.toFixed(4));
+    const target = source.trajectory?.[state.selectedKeyframeIndex]?.position ?? source.position;
+    target[0] = Number(x.toFixed(4));
+    target[1] = Number(y.toFixed(4));
+    synchronizeSourcePosition(source);
     syncSourceEditor();
     markChanged("위치 변경됨");
     renderSourceCards();
@@ -95,6 +109,7 @@ function createAssetBackedSource(descriptor, file) {
   changeSignalType(source, "asset", descriptor.id);
   state.scene.sources.push(source);
   state.selectedSourceId = source.id;
+  state.selectedKeyframeIndex = 0;
   return source;
 }
 
@@ -137,7 +152,10 @@ function syncImagePlane() {
 
 function renderCanvas() {
   if (!state.scene) return;
-  canvasView.render(state.scene, state.imageElement, state.viewPlane, state.selectedSourceId);
+  canvasView.render(
+    state.scene, state.imageElement, state.viewPlane, state.selectedSourceId,
+    state.previewTime, state.selectedKeyframeIndex,
+  );
 }
 
 function renderSourceCards() {
@@ -159,10 +177,12 @@ function renderSourceCards() {
     const signal = document.createElement("small");
     signal.textContent = describeSignal(source.signal);
     const position = document.createElement("small");
-    position.textContent = `x ${source.position[0].toFixed(2)} · y ${source.position[1].toFixed(2)} · z ${source.position[2].toFixed(2)} m`;
+    const motion = Array.isArray(source.trajectory) ? ` · 이동 ${source.trajectory.length}점` : "";
+    position.textContent = `x ${source.position[0].toFixed(2)} · y ${source.position[1].toFixed(2)} · z ${source.position[2].toFixed(2)} m${motion}`;
     button.append(heading, signal, position);
     button.addEventListener("click", () => {
       state.selectedSourceId = source.id;
+      state.selectedKeyframeIndex = 0;
       renderSourceCards();
       syncSourceEditor();
       renderCanvas();
@@ -193,6 +213,104 @@ function fillAudioSelect(select, selectedId, placeholder) {
   select.value = selectedId ?? "";
 }
 
+function syncPreviewTime() {
+  const maximum = Math.max(0, Number(state.scene?.duration) || 0);
+  state.previewTime = Math.max(0, Math.min(maximum, state.previewTime));
+  elements["preview-time"].max = String(maximum);
+  elements["preview-time"].step = String(Math.max(0.001, Math.min(0.01, maximum / 100 || 0.01)));
+  elements["preview-time"].value = String(state.previewTime);
+  elements["preview-time-value"].value = `${state.previewTime.toFixed(2)} s`;
+  elements["preview-time-value"].textContent = `${state.previewTime.toFixed(2)} s`;
+}
+
+function trajectoryNumberField(label, value, options, onChange) {
+  const field = document.createElement("label");
+  field.className = "field";
+  const title = document.createElement("span");
+  title.textContent = label;
+  const input = document.createElement("input");
+  input.type = "number";
+  input.value = String(value);
+  input.step = String(options.step ?? 0.01);
+  if (Number.isFinite(options.min)) input.min = String(options.min);
+  if (Number.isFinite(options.max)) input.max = String(options.max);
+  input.addEventListener("change", () => {
+    if (!Number.isFinite(input.valueAsNumber)) {
+      input.value = String(value);
+      return;
+    }
+    onChange(input.valueAsNumber);
+  });
+  field.append(title, input);
+  return field;
+}
+
+function renderTrajectoryEditor(source) {
+  const moving = Array.isArray(source.trajectory);
+  elements["source-motion"].checked = moving;
+  elements["trajectory-fields"].classList.toggle("is-hidden", !moving);
+  syncPreviewTime();
+  const list = elements["trajectory-list"];
+  list.replaceChildren();
+  if (!moving) return;
+  state.selectedKeyframeIndex = Math.max(0, Math.min(source.trajectory.length - 1, state.selectedKeyframeIndex));
+  source.trajectory.forEach((keyframe, index) => {
+    const row = document.createElement("div");
+    row.className = "trajectory-row";
+    row.dataset.keyframeIndex = String(index);
+    const select = document.createElement("button");
+    select.type = "button";
+    select.className = "trajectory-row__select";
+    select.classList.toggle("is-selected", index === state.selectedKeyframeIndex);
+    select.textContent = String(index + 1);
+    select.title = `${index + 1}번 경로점 선택`;
+    select.addEventListener("click", () => {
+      state.selectedKeyframeIndex = index;
+      state.previewTime = keyframe.time;
+      renderTrajectoryEditor(source);
+      renderCanvas();
+    });
+    const bounds = trajectoryTimeBounds(source, index, state.scene.duration);
+    const time = trajectoryNumberField("t (s)", keyframe.time, { min: bounds.minimum, max: bounds.maximum }, (value) => {
+      state.previewTime = updateTrajectoryKeyframeTime(source, index, value, state.scene.duration);
+      syncSourceEditor();
+      renderCanvas();
+      markChanged("경로 시간 변경됨");
+    });
+    const coordinates = ["x", "y", "z"].map((axis, coordinateIndex) =>
+      trajectoryNumberField(`${axis} (m)`, keyframe.position[coordinateIndex], {
+        min: coordinateIndex === 2 ? 0.01 : undefined,
+        step: coordinateIndex === 2 ? 0.1 : 0.01,
+      }, (value) => {
+        keyframe.position[coordinateIndex] = value;
+        synchronizeSourcePosition(source);
+        state.previewTime = keyframe.time;
+        syncSourceEditor();
+        renderSourceCards();
+        renderCanvas();
+        markChanged("경로 위치 변경됨");
+      }),
+    );
+    const remove = document.createElement("button");
+    remove.type = "button";
+    remove.className = "trajectory-row__remove";
+    remove.textContent = "×";
+    remove.title = "경로점 삭제";
+    remove.disabled = source.trajectory.length <= 2;
+    remove.addEventListener("click", () => {
+      if (!removeTrajectoryKeyframe(source, index)) return;
+      state.selectedKeyframeIndex = Math.min(state.selectedKeyframeIndex, source.trajectory.length - 1);
+      syncSourceEditor();
+      renderSourceCards();
+      renderCanvas();
+      markChanged("경로점 삭제됨");
+    });
+    row.append(select, time, ...coordinates, remove);
+    list.append(row);
+  });
+  elements["add-keyframe-button"].disabled = source.trajectory.length >= MAX_TRAJECTORY_KEYFRAMES;
+}
+
 function syncSourceEditor() {
   const source = selectedSource();
   elements["no-source-message"].classList.toggle("is-hidden", Boolean(source));
@@ -206,6 +324,7 @@ function syncSourceEditor() {
   setNumber(elements["source-start"], source.startTime);
   setNumber(elements["source-duration"], source.duration);
   elements["source-type"].value = source.signal.type;
+  renderTrajectoryEditor(source);
   elements["tone-fields"].classList.toggle("is-hidden", source.signal.type !== "tone");
   elements["noise-fields"].classList.toggle("is-hidden", source.signal.type !== "noise");
   elements["asset-fields"].classList.toggle("is-hidden", source.signal.type !== "asset");
@@ -532,7 +651,15 @@ function bindSceneControls() {
     elements["workspace-title"].textContent = input.value || "이름 없는 장면";
   });
   bindInput("scene-id", (input) => { state.scene.id = input.value; });
-  bindInput("scene-duration", (input) => { state.scene.duration = numberFrom(input); });
+  bindInput("scene-duration", (input) => {
+    const previousDuration = state.scene.duration;
+    const nextDuration = numberFrom(input);
+    state.scene.duration = nextDuration;
+    scaleSceneTrajectories(state.scene, previousDuration, nextDuration);
+    syncPreviewTime();
+    syncSourceEditor();
+    renderCanvas();
+  });
   bindInput("sample-rate", (input) => {
     state.scene.sampleRate = Number(input.value);
     state.decodedAudio.clear();
@@ -571,6 +698,7 @@ function bindSourceControls() {
     const source = createSource(state.scene);
     state.scene.sources.push(source);
     state.selectedSourceId = source.id;
+    state.selectedKeyframeIndex = 0;
     renderSourceCards();
     syncSourceEditor();
     renderCanvas();
@@ -583,6 +711,7 @@ function bindSourceControls() {
     }
     state.scene.sources = state.scene.sources.filter((source) => source.id !== state.selectedSourceId);
     state.selectedSourceId = state.scene.sources[0].id;
+    state.selectedKeyframeIndex = 0;
     renderSourceCards();
     syncSourceEditor();
     renderCanvas();
@@ -593,7 +722,12 @@ function bindSourceControls() {
   for (const [id, index] of [["source-x", 0], ["source-y", 1], ["source-z", 2]]) {
     bindInput(id, (input) => {
       selectedSource().position[index] = numberFrom(input);
+      if (selectedSource().trajectory) {
+        selectedSource().trajectory[0].position[index] = numberFrom(input);
+        synchronizeSourcePosition(selectedSource());
+      }
       renderSourceCards();
+      renderTrajectoryEditor(selectedSource());
       renderCanvas();
     });
   }
@@ -611,6 +745,41 @@ function bindSourceControls() {
   bindInput("source-asset", (input) => { selectedSource().signal.assetId = input.value; renderSourceCards(); }, "change");
   bindInput("source-channel", (input) => { selectedSource().signal.channel = numberFrom(input); });
   bindInput("source-loop", (input) => { selectedSource().signal.loop = input.checked; }, "change");
+
+  elements["source-motion"].addEventListener("change", () => {
+    const source = selectedSource();
+    if (elements["source-motion"].checked) {
+      enableSourceTrajectory(source, state.scene.duration, state.viewPlane);
+      state.selectedKeyframeIndex = 0;
+      state.previewTime = 0;
+    } else {
+      disableSourceTrajectory(source);
+      state.selectedKeyframeIndex = 0;
+    }
+    syncSourceEditor();
+    renderSourceCards();
+    renderCanvas();
+    markChanged(elements["source-motion"].checked ? "이동 경로 켜짐" : "이동 경로 꺼짐");
+  });
+  elements["preview-time"].addEventListener("input", () => {
+    state.previewTime = numberFrom(elements["preview-time"]);
+    syncPreviewTime();
+    renderCanvas();
+  });
+  elements["add-keyframe-button"].addEventListener("click", () => {
+    const source = selectedSource();
+    const insertedIndex = insertTrajectoryKeyframe(source);
+    if (insertedIndex < 0) {
+      setStatus(`경로점은 최대 ${MAX_TRAJECTORY_KEYFRAMES.toLocaleString()}개까지 추가할 수 있습니다.`);
+      return;
+    }
+    state.selectedKeyframeIndex = insertedIndex;
+    state.previewTime = source.trajectory[insertedIndex].time;
+    syncSourceEditor();
+    renderSourceCards();
+    renderCanvas();
+    markChanged("경로점 추가됨");
+  });
 }
 
 async function handleAudioFiles(files, { createSources = false } = {}) {
@@ -784,6 +953,8 @@ function bindFileControls() {
       state.assetErrors.clear();
       state.scene = prepareSceneForEditing(candidate);
       state.selectedSourceId = state.scene.sources[0].id;
+      state.selectedKeyframeIndex = 0;
+      state.previewTime = 0;
       state.viewPlane = state.scene.image
         ? {
             xMin: state.scene.image.plane.xMin, xMax: state.scene.image.plane.xMax,
@@ -851,6 +1022,8 @@ async function initialize() {
   state.scene = prepareSceneForEditing(await response.json());
   state.scene.id = createSceneId();
   state.selectedSourceId = state.scene.sources[0].id;
+  state.selectedKeyframeIndex = 0;
+  state.previewTime = 0;
   if (state.scene.image) {
     state.viewPlane = {
       xMin: state.scene.image.plane.xMin, xMax: state.scene.image.plane.xMax,

apps/dataset-builder/model.js

@@ -7,11 +7,123 @@ export const DEFAULT_VIEW_PLANE = Object.freeze({
 
 export const SOURCE_COLORS = ["#65f2bf", "#58c7e8", "#ffc56e", "#ff8f87", "#be9bff", "#8ee36b"];
 
+export const MAX_TRAJECTORY_KEYFRAMES = 4096;
+
+function copyPosition(position) {
+  return position.map((coordinate) => Number(coordinate));
+}
+
+function clamp(value, minimum, maximum) {
+  return Math.max(minimum, Math.min(maximum, value));
+}
+
+export function synchronizeSourcePosition(source) {
+  if (Array.isArray(source.trajectory) && source.trajectory.length > 0) {
+    source.position = copyPosition(source.trajectory[0].position);
+  }
+  return source.position;
+}
+
+export function createDefaultTrajectory(source, sceneDuration, plane = DEFAULT_VIEW_PLANE) {
+  const start = copyPosition(source.position);
+  const width = Number.isFinite(plane?.xMax - plane?.xMin) && plane.xMax > plane.xMin
+    ? plane.xMax - plane.xMin
+    : DEFAULT_VIEW_PLANE.xMax - DEFAULT_VIEW_PLANE.xMin;
+  const minimum = Number.isFinite(plane?.xMin) ? plane.xMin : DEFAULT_VIEW_PLANE.xMin;
+  const maximum = Number.isFinite(plane?.xMax) ? plane.xMax : DEFAULT_VIEW_PLANE.xMax;
+  const offset = Math.max(0.1, width * 0.25);
+  const rightRoom = maximum - start[0];
+  const leftRoom = start[0] - minimum;
+  const direction = rightRoom >= offset || rightRoom >= leftRoom ? 1 : -1;
+  const endX = clamp(start[0] + direction * offset, minimum, maximum);
+  return [
+    { time: 0, position: start },
+    { time: sceneDuration, position: [endX, start[1], start[2]] },
+  ];
+}
+
+export function enableSourceTrajectory(source, sceneDuration, plane = DEFAULT_VIEW_PLANE) {
+  if (!Array.isArray(source.trajectory) || source.trajectory.length < 2) {
+    source.trajectory = createDefaultTrajectory(source, sceneDuration, plane);
+  }
+  synchronizeSourcePosition(source);
+  return source.trajectory;
+}
+
+export function disableSourceTrajectory(source) {
+  synchronizeSourcePosition(source);
+  delete source.trajectory;
+}
+
+export function insertTrajectoryKeyframe(source) {
+  if (!Array.isArray(source.trajectory) || source.trajectory.length < 2 ||
+      source.trajectory.length >= MAX_TRAJECTORY_KEYFRAMES) {
+    return -1;
+  }
+  let leftIndex = 0;
+  let largestGap = -Infinity;
+  for (let index = 0; index < source.trajectory.length - 1; index += 1) {
+    const gap = source.trajectory[index + 1].time - source.trajectory[index].time;
+    if (gap > largestGap) {
+      largestGap = gap;
+      leftIndex = index;
+    }
+  }
+  if (!(largestGap > 0)) return -1;
+  const left = source.trajectory[leftIndex];
+  const right = source.trajectory[leftIndex + 1];
+  source.trajectory.splice(leftIndex + 1, 0, {
+    time: left.time + largestGap / 2,
+    position: left.position.map((coordinate, index) =>
+      coordinate + (right.position[index] - coordinate) / 2,
+    ),
+  });
+  synchronizeSourcePosition(source);
+  return leftIndex + 1;
+}
+
+export function removeTrajectoryKeyframe(source, index) {
+  if (!Array.isArray(source.trajectory) || source.trajectory.length <= 2 ||
+      !Number.isInteger(index) || index < 0 || index >= source.trajectory.length) return false;
+  source.trajectory.splice(index, 1);
+  synchronizeSourcePosition(source);
+  return true;
+}
+
+export function trajectoryTimeBounds(source, index, sceneDuration) {
+  const trajectory = source.trajectory;
+  const duration = Number.isFinite(sceneDuration) && sceneDuration > 0 ? sceneDuration : 0;
+  const gap = Math.max(1e-9, duration * 1e-9);
+  return {
+    minimum: index === 0 ? 0 : trajectory[index - 1].time + gap,
+    maximum: index === trajectory.length - 1 ? duration : trajectory[index + 1].time - gap,
+  };
+}
+
+export function updateTrajectoryKeyframeTime(source, index, requestedTime, sceneDuration) {
+  if (!Number.isFinite(requestedTime) || !source.trajectory?.[index]) return source.trajectory?.[index]?.time;
+  const { minimum, maximum } = trajectoryTimeBounds(source, index, sceneDuration);
+  source.trajectory[index].time = clamp(requestedTime, minimum, maximum);
+  return source.trajectory[index].time;
+}
+
+export function scaleSceneTrajectories(scene, previousDuration, nextDuration) {
+  if (!Number.isFinite(previousDuration) || previousDuration <= 0 ||
+      !Number.isFinite(nextDuration) || nextDuration <= 0) return;
+  const scale = nextDuration / previousDuration;
+  for (const source of scene.sources) {
+    if (!Array.isArray(source.trajectory)) continue;
+    source.trajectory.forEach((keyframe) => { keyframe.time *= scale; });
+    synchronizeSourcePosition(source);
+  }
+}
+
 export function prepareSceneForEditing(scene) {
   const prepared = structuredClone(scene);
   prepared.assets ??= [];
   prepared.ambient ??= [];
   prepared.mix ??= { normalization: "none", targetPeak: 0.95 };
+  prepared.sources.forEach(synchronizeSourcePosition);
   return prepared;
 }
 

apps/dataset-builder/styles.css

@@ -458,6 +458,76 @@
   line-height: 1.5;
 }
 
+.trajectory-editor {
+  margin: 12px 0;
+  padding: 12px;
+  border: 1px solid rgb(101 242 191 / 16%);
+  border-radius: 12px;
+  background: rgb(101 242 191 / 3%);
+}
+
+.trajectory-toggle {
+  min-height: 28px;
+}
+
+.trajectory-preview {
+  margin-top: 12px;
+}
+
+.trajectory-preview output {
+  color: var(--mint);
+  font: 700 0.7rem ui-monospace, SFMono-Regular, Consolas, monospace;
+}
+
+.trajectory-preview input[type="range"] {
+  min-height: 28px;
+  padding: 0;
+  accent-color: var(--mint);
+}
+
+.trajectory-list {
+  display: grid;
+  gap: 8px;
+  margin: 12px 0 10px;
+}
+
+.trajectory-row {
+  display: grid;
+  grid-template-columns: 42px repeat(4, minmax(0, 1fr)) 30px;
+  gap: 5px;
+  align-items: end;
+}
+
+.trajectory-row__select,
+.trajectory-row__remove {
+  min-height: 36px;
+  padding: 6px;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  color: var(--muted);
+  background: #0b1714;
+  cursor: pointer;
+}
+
+.trajectory-row__select.is-selected {
+  border-color: var(--mint);
+  color: var(--mint);
+}
+
+.trajectory-row__remove:disabled {
+  cursor: not-allowed;
+  opacity: 0.3;
+}
+
+.trajectory-row .field > span {
+  font-size: 0.6rem;
+}
+
+.trajectory-row .field input {
+  min-height: 36px;
+  padding: 6px;
+}
+
 .is-hidden {
   display: none !important;
 }
@@ -563,4 +633,13 @@
   .field-grid--three {
     grid-template-columns: 1fr;
   }
+
+  .trajectory-row {
+    grid-template-columns: 38px repeat(2, minmax(0, 1fr)) 30px;
+  }
+
+  .trajectory-row .field:nth-of-type(3),
+  .trajectory-row .field:nth-of-type(4) {
+    grid-row: 2;
+  }
 }