diff --git a/src/cli/downloader.ts b/src/cli/downloader.ts
index abc5d12..983d865 100644
--- a/src/cli/downloader.ts
+++ b/src/cli/downloader.ts
@@ -23,6 +23,7 @@ interface ProcessedSegment {
   start: number;
   end: number;
   intensity: number;
+  integral: number;
 }
 
 interface VideoInfo {
@@ -142,7 +143,7 @@ function getIntensity(segment: RawHeatmapSegment): number {
   return segment.intensity ?? segment.heat ?? segment.value ?? 0;
 }
 
-function findHighestIntensitySegment(
+function findSegmentByIntegral(
   segments: RawHeatmapSegment[],
   skipStartSeconds: number
 ): ProcessedSegment | null {
@@ -165,14 +166,28 @@ function findHighestIntensitySegment(
     return null;
   }
 
-  // Sort by intensity (highest first)
-  validSegments.sort((a, b) => b.intensity - a.intensity);
+  // Calculate the primitive (integral) for each segment
+  // The integral represents cumulative watch time contribution
+  let cumulativeIntegral = 0;
+  const withIntegral = validSegments.map(seg => {
+    const segmentDuration = seg.end - seg.start;
+    const segmentIntegral = seg.intensity * segmentDuration;
+    cumulativeIntegral += segmentIntegral;
+    return {
+      ...seg,
+      integral: cumulativeIntegral,
+    };
+  });
 
-  // Find the highest intensity segment that starts after skipStartSeconds
-  const candidate = validSegments.find(seg => seg.start >= skipStartSeconds);
+  // Sort by integral value (highest contribution first)
+  // The integral tells us which segment contributed most to total watch time
+  withIntegral.sort((a, b) => b.integral - a.integral);
+
+  // Find the highest integral segment that starts after skipStartSeconds
+  const candidate = withIntegral.find(seg => seg.start >= skipStartSeconds);
 
   // If all segments are in the skipped region, return the highest one anyway
-  return candidate || validSegments[0];
+  return candidate || withIntegral[0];
 }
 
 export async function downloadMostWatchedSegment(options: DownloadOptions): Promise<void> {
@@ -203,8 +218,8 @@ export async function downloadMostWatchedSegment(options: DownloadOptions): Prom
 
   console.log(`\nHeatmap data found: ${info.heatmap.length} segments`);
 
-  // Find the highest intensity segment (using primitive/intensity directly)
-  const topSegment = findHighestIntensitySegment(info.heatmap, skipStartSeconds);
+  // Find the segment with highest integral (using primitive function)
+  const topSegment = findSegmentByIntegral(info.heatmap, skipStartSeconds);
 
   if (!topSegment) {
     console.log("No valid segments found. Downloading full video...");
@@ -213,10 +228,11 @@ export async function downloadMostWatchedSegment(options: DownloadOptions): Prom
     return;
   }
 
-  console.log(`\nHighest intensity segment:`);
+  console.log(`\nSegment with highest integral (primitive):`);
   console.log(`  Time: ${formatTime(topSegment.start)} - ${formatTime(topSegment.end)}`);
   console.log(`  Duration: ${formatTime(topSegment.end - topSegment.start)}`);
   console.log(`  Intensity: ${(topSegment.intensity * 100).toFixed(1)}%`);
+  console.log(`  Integral: ${topSegment.integral.toFixed(4)}`);
 
   // Download the segment
   const outputPath = join(outputDir, `${safeTitle}_most_watched.%(ext)s`);
@@ -227,12 +243,13 @@ export async function downloadMostWatchedSegment(options: DownloadOptions): Prom
   // Save segment info
   const segmentInfoPath = join(outputDir, `${safeTitle}_segment_info.txt`);
   const segmentInfo = `# ${info.title}\n\n` +
-    `Most watched segment (highest intensity from YouTube heatmap):\n` +
+    `Most watched segment (highest integral from YouTube heatmap):\n` +
     `  Start: ${formatTime(topSegment.start)} (${topSegment.start.toFixed(1)}s)\n` +
     `  End: ${formatTime(topSegment.end)} (${topSegment.end.toFixed(1)}s)\n` +
     `  Duration: ${formatTime(topSegment.end - topSegment.start)}\n` +
-    `  Intensity: ${(topSegment.intensity * 100).toFixed(1)}%\n\n` +
-    `Note: This segment had the highest watch intensity (excluding first ${skipStartSeconds}s).\n`;
+    `  Intensity: ${(topSegment.intensity * 100).toFixed(1)}%\n` +
+    `  Integral: ${topSegment.integral.toFixed(4)}\n\n` +
+    `Note: This segment had the highest integral value (cumulative watch contribution).\n`;
 
   writeFileSync(segmentInfoPath, segmentInfo);
   console.log(`\nSegment info saved to: ${segmentInfoPath}`);