Fix exports that added a fake Intro clip, lost OFFSET footage, and broke YouTube chapters

src/utils/markers.test.ts

@@ -97,6 +97,7 @@ describe("buildSegments", () => {
         vodEnd: 600,
         startTime: 0,
         endTime: 610,
+        isIntro: true,
       },
       {
         type: "start",
@@ -152,33 +153,53 @@ describe("buildSegments", () => {
     const segments = buildSegments({
       markers: [
         marker(100, "Before camera"),
-        marker(300, "OFFSET 00:05:00"),
+        marker(300, "OFFSET 00:06:40"),
         marker(400, "On camera"),
       ],
       videoSeconds: 1000,
-      offsetSeconds: 350,
+      offsetSeconds: 400,
       bufferSeconds: 0,
     });
 
     expect(segments).toEqual([
       {
         type: "offset",
-        label: "00:05:00",
+        label: "00:06:40",
         vodStart: 300,
         vodEnd: 400,
         startTime: 0,
-        endTime: 50,
+        endTime: 0,
       },
       {
         type: "start",
         label: "On camera",
         vodStart: 400,
         vodEnd: 1000,
-        startTime: 50,
-        endTime: 650,
+        startTime: 0,
+        endTime: 600,
       },
     ]);
   });
+
+  it("does not end a clip at an offset marker", () => {
+    const segments = buildSegments({
+      markers: [
+        marker(0, "Chrome"),
+        marker(300, "OFFSET 00:04:00"),
+        marker(600, "React"),
+      ],
+      videoSeconds: 900,
+      offsetSeconds: 240,
+      bufferSeconds: 0,
+    });
+
+    expect(segments.map((s) => [s.label, s.vodStart, s.vodEnd])).toEqual([
+      ["Chrome", 0, 600],
+      ["00:04:00", 300, 600],
+      ["React", 600, 900],
+    ]);
+    expect(toCsv(segments)).toBe(["0,360,Chrome", "360,660,React"].join("\n"));
+  });
 });
 
 describe("exports", () => {
@@ -192,17 +213,15 @@ describe("exports", () => {
     videoSeconds: 27 * 3600,
   });
 
-  it("writes only start clips to the CSV, quoting labels when needed", () => {
+  it("writes only marked start clips to the CSV, quoting labels when needed", () => {
     expect(toCsv(segments)).toBe(
-      [
-        "0,15,Intro",
-        '0,70,"React, Vue, and ""Svelte"""',
-        "93590,97210,Late night",
-      ].join("\n")
+      ['0,100,"React, Vue, and ""Svelte"""', "93590,97210,Late night"].join(
+        "\n"
+      )
     );
   });
 
-  it("starts YouTube chapters at 00:00:00 when the offset skips early clips", () => {
+  it("adds an Intro chapter when the offset skips early clips", () => {
     const offsetSegments = buildSegments({
       markers: [
         marker(100, "Before camera"),
@@ -212,7 +231,26 @@ describe("exports", () => {
       videoSeconds: 1000,
       offsetSeconds: 350,
     });
-    expect(toYouTubeChapters(offsetSegments)).toBe("00:00:00 On camera");
+    expect(toYouTubeChapters(offsetSegments)).toBe(
+      ["00:00:00 Intro", "00:00:40 On camera"].join("\n")
+    );
+  });
+
+  it("drops a YouTube chapter shorter than 10 seconds and keeps the later one", () => {
+    const shortSegments = buildSegments({
+      markers: [
+        // With the 10s buffer, Chrome starts 2s after the intro
+        marker(12, "Chrome"),
+        marker(100, "React"),
+        // 5s after React
+        marker(105, "Vue"),
+        marker(300, "Svelte"),
+      ],
+      videoSeconds: 600,
+    });
+    expect(toYouTubeChapters(shortSegments)).toBe(
+      ["00:00:00 Chrome", "00:01:35 Vue", "00:04:50 Svelte"].join("\n")
+    );
   });
 
   it("keeps one YouTube chapter per timestamp", () => {

src/utils/markers.ts

@@ -21,6 +21,8 @@ export type Segment = {
   // Bounds in the exported footage, with offset and buffer applied
   startTime: number;
   endTime: number;
+  // Only set on the fake "Intro" clip that buildSegments adds
+  isIntro?: true;
 };
 
 // Seconds of padding on each side of an exported clip
@@ -92,7 +94,8 @@ export function formatSeconds(totalSeconds: number): string {
   )}:${pad(seconds % 60)}`;
 }
 
-// Each marker runs until the next one (or the end of the VOD).
+// Each marker runs until the next start or end marker (or the end of the VOD).
+// Offset markers only set the offset, so they never end a clip.
 // Start clips that end before the offset are dropped, since they are not in
 // the offset footage.
 export function buildSegments(opts: {
@@ -117,19 +120,26 @@ export function buildSegments(opts: {
 
   // Add a fake "Intro" start marker at 0, unless a real start marker is there.
   // It goes after other markers at 0, so it runs until the next real marker.
+  // YouTube chapters use it to label the start. The CSV leaves it out.
   const hasStartAtZero = markers.some(
     (m) => m.vodStart === 0 && m.type === "start"
   );
   const withIntro = hasStartAtZero
     ? markers
     : [
         ...markers.filter((m) => m.vodStart === 0),
-        { vodStart: 0, type: "start" as const, label: "Intro" },
+        {
+          vodStart: 0,
+          type: "start" as const,
+          label: "Intro",
+          isIntro: true as const,
+        },
         ...markers.filter((m) => m.vodStart > 0),
       ];
 
   return withIntro.flatMap((marker, i) => {
-    const vodEnd = withIntro[i + 1]?.vodStart ?? opts.videoSeconds;
+    const nextMarker = withIntro.slice(i + 1).find((m) => m.type !== "offset");
+    const vodEnd = nextMarker?.vodStart ?? opts.videoSeconds;
     if (marker.type === "start" && vodEnd <= offset) return [];
 
     return {
@@ -144,24 +154,39 @@ export function buildSegments(opts: {
 const toCsvField = (value: string) =>
   /[",\r\n]/.test(value) ? `"${value.replaceAll('"', '""')}"` : value;
 
-// CSV for LosslessCut: "start,end,label" per clip, in seconds
+// CSV for LosslessCut: "start,end,label" per clip, in seconds.
+// Only clips you marked. The fake intro is left out.
 export function toCsv(segments: Segment[]): string {
   return segments
-    .filter((s) => s.type === "start")
+    .filter((s) => s.type === "start" && !s.isIntro)
     .map((s) => `${s.startTime},${s.endTime},${toCsvField(s.label)}`)
     .join("\n");
 }
 
-// YouTube needs the first chapter at 00:00:00 and rejects chapters that
-// share a timestamp. When several clips start at the same time, only the
-// last one is kept.
+// YouTube ignores all chapters unless the first one is at 00:00:00
+// and each one is at least 10 seconds long.
+const MIN_CHAPTER_SECONDS = 10;
+
+// One chapter per start clip.
+// With an offset, the first clip can start after 00:00:00. Then an "Intro"
+// chapter at 00:00:00 labels the footage before it.
+// When a chapter starts less than 10 seconds after the one before it, the
+// earlier one is dropped. If that was the first chapter, the next one moves
+// to 00:00:00.
 export function toYouTubeChapters(segments: Segment[]): string {
   const clips = segments.filter((s) => s.type === "start");
-  return clips
-    .filter((clip, i) => clips[i + 1]?.startTime !== clip.startTime)
+  const intro =
+    (clips[0]?.startTime ?? 0) > 0 ? [{ startTime: 0, label: "Intro" }] : [];
+  const chapters = [...intro, ...clips];
+
+  return chapters
+    .filter((chapter, i) => {
+      const next = chapters[i + 1];
+      return !next || next.startTime - chapter.startTime >= MIN_CHAPTER_SECONDS;
+    })
     .map(
-      (clip, i) =>
-        `${formatSeconds(i === 0 ? 0 : clip.startTime)} ${clip.label}`
+      (chapter, i) =>
+        `${formatSeconds(i === 0 ? 0 : chapter.startTime)} ${chapter.label}`
     )
     .join("\n");
 }