fix(export): stop a voiceover piece where the next one starts

src/native/sceneDescription.test.ts

@@ -2723,6 +2723,18 @@ describe("buildSceneDescription.audioTracks", () => {
 		expect(entries[1]).toMatchObject({ startSec: 4, trimStartSec: 6, trimEndSec: 10 });
 	});
 
+	it("stops a piece where the next one starts when a speed region sits before the cut", () => {
+		// Issue #1283. A 2x region over raw 0..2 saves 1s, so the piece after the cut lands at
+		// output 3. Played whole at 1x, raw 0..4 ran to output 4: two pieces at once for 1s.
+		const doc = { ...cutDoc([voice]) };
+		doc.legacyEditor = { speedRegions: [{ id: "s", startMs: 0, endMs: 2000, speed: 2 }] };
+		const entries = buildSceneDescription(doc).audioTracks;
+		expect(entries.map((e) => [e.startSec, e.trimStartSec, e.trimEndSec])).toEqual([
+			[0, 0, 3],
+			[3, 6, 10],
+		]);
+	});
+
 	it("keeps the fades on the take's outer edges across a split", () => {
 		const entries = buildSceneDescription(
 			cutDoc([{ ...voice, fadeInMs: 500, fadeOutMs: 500 }]),

src/native/sceneDescription.ts

@@ -982,11 +982,22 @@ export function buildSceneDescription(
 				}))
 				.filter((entry) => entry.trimEndSec > entry.trimStartSec);
 			// The fades belong to the TAKE's edges, not to every piece a cut left behind.
-			return kept.map((entry, i) => ({
-				...entry,
-				fadeInSec: i === 0 ? base.fadeInSec : 0,
-				fadeOutSec: i === kept.length - 1 ? base.fadeOutSec : 0,
-			}));
+			return kept.map((entry, i) => {
+				// A piece plays at 1x, but its head and the next one's are projected through the
+				// speed regions: a sped-up stretch between them leaves the piece longer than the
+				// output gap, so it would still be playing when the next one starts (#1283). It
+				// stops where the next piece begins.
+				const next = kept[i + 1];
+				const trimEndSec = next
+					? Math.min(entry.trimEndSec, entry.trimStartSec + next.startSec - entry.startSec)
+					: entry.trimEndSec;
+				return {
+					...entry,
+					trimEndSec,
+					fadeInSec: i === 0 ? base.fadeInSec : 0,
+					fadeOutSec: i === kept.length - 1 ? base.fadeOutSec : 0,
+				};
+			});
 		}
 		if (!track.loop) {
 			return [