fix: prevent duplicate frames at trimmed speed boundaries

crates/compositor/src/regions.rs

@@ -49,18 +49,22 @@ pub fn speed_segments_for_window(
     for region in overlapping {
         let start = region.start_sec.max(source_start_sec).max(cursor);
         let end = region.end_sec.min(source_end_sec);
+        // Projection can leave a zero-width region at a trim boundary. It may still pass
+        // the overlap filter when rounding puts its start just inside the clip window. Skip
+        // it before emitting the 1x gap, or the unchanged cursor makes that gap render twice.
+        if end <= start {
+            continue;
+        }
         if start > cursor {
             push_speed_segment(&mut spans, cursor, start, 1.0, fps);
         }
-        if end > start {
-            let speed = if region.speed.is_finite() && region.speed > 0.0 {
-                region.speed
-            } else {
-                1.0
-            };
-            push_speed_segment(&mut spans, start, end, speed, fps);
-            cursor = end;
-        }
+        let speed = if region.speed.is_finite() && region.speed > 0.0 {
+            region.speed
+        } else {
+            1.0
+        };
+        push_speed_segment(&mut spans, start, end, speed, fps);
+        cursor = end;
     }
     if cursor < source_end_sec {
         push_speed_segment(&mut spans, cursor, source_end_sec, 1.0, fps);
@@ -3133,6 +3137,16 @@ mod exporter_frame_totals {
             60,
             "région débordant la fenêtre gardée"
         );
+        let issue_876_fps = 60.0;
+        let first_clip = frames(
+            0.0,
+            44.81830642526596,
+            &[region(44.818, 44.818, 1.5)],
+            issue_876_fps,
+        );
+        let second_clip = frames(0.0, 47.833333, &[region(0.0, 1.87, 1.5)], issue_876_fps);
+        assert_eq!(first_clip, 2690, "une région vide ne double pas le premier clip");
+        assert_eq!(first_clip + second_clip, 5523, "total corrigé du repro #876");
         assert_eq!(
             frames(
                 0.0,

src/lib/exporter/outputFrameCount.test.ts

@@ -60,6 +60,21 @@ describe("outputFrameCount", () => {
 		).toBe(60);
 	});
 
+	it("does not double-count a clip for an empty speed region at its trimmed edge (#876)", () => {
+		const clips = [
+			{ sourceStartSec: 0, sourceEndSec: 44.81830642526596 },
+			{ sourceStartSec: 0, sourceEndSec: 47.833333 },
+		];
+		const regions = [
+			{ startSec: 44.818, endSec: 44.818, speed: 1.5, clipIndex: 0 },
+			{ startSec: 0, endSec: 1.87, speed: 1.5, clipIndex: 1 },
+		];
+
+		// The first region is empty after trim projection. Before the fix it caused the first
+		// clip's normal-speed prefix to be counted twice, yielding the reported 8,213 frames.
+		expect(outputFrameCount(clips, regions, 60)).toBe(5_523);
+	});
+
 	it("never renders the same source time twice when two regions overlap", () => {
 		// A stale payload can overlap; the first region keeps the covered portion, matching
 		// `speed_segments_for_window`'s cursor.

src/lib/exporter/outputFrameCount.ts

@@ -75,14 +75,18 @@ export function clipOutputFrameCount(
 	for (const region of overlapping) {
 		const start = Math.max(region.startSec, sourceStartSec, cursor);
 		const end = Math.min(region.endSec, sourceEndSec);
+		// Projection can leave a zero-width region at a trim boundary. It may still pass
+		// the overlap filter when rounding puts its start just inside the clip window. Skip
+		// it before emitting the 1x gap, or the unchanged cursor makes that gap render twice.
+		if (end <= start) {
+			continue;
+		}
 		if (start > cursor) {
 			frames += segmentFrames(cursor, start, 1, fps);
 		}
-		if (end > start) {
-			const speed = Number.isFinite(region.speed) && region.speed > 0 ? region.speed : 1;
-			frames += segmentFrames(start, end, speed, fps);
-			cursor = end;
-		}
+		const speed = Number.isFinite(region.speed) && region.speed > 0 ? region.speed : 1;
+		frames += segmentFrames(start, end, speed, fps);
+		cursor = end;
 	}
 	if (cursor < sourceEndSec) {
 		frames += segmentFrames(cursor, sourceEndSec, 1, fps);