Improve subtitle fragment finder for gaps in live playlists

video-dev · May 29, 2021 · 702447e · 702447e
1 parent 35bc1d7
commit 702447e
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Showing 3 changed files with 60 additions and 9 deletions.
diff --git a/src/controller/fragment-finders.ts b/src/controller/fragment-finders.ts
@@ -63,7 +63,9 @@ export function findFragmentByPTS(
   let fragNext: Fragment | null = null;
   if (fragPrevious) {
     fragNext =
-      fragments[(fragPrevious.sn as number) - (fragments[0].sn as number) + 1];
+      fragments[
+        (fragPrevious.sn as number) - (fragments[0].sn as number) + 1
+      ] || null;
   } else if (bufferEnd === 0 && fragments[0].start === 0) {
     fragNext = fragments[0];
   }

diff --git a/src/controller/subtitle-stream-controller.ts b/src/controller/subtitle-stream-controller.ts
@@ -288,14 +288,17 @@ export class SubtitleStreamController
             fragPrevious.endProgramDateTime,
             maxFragLookUpTolerance
           );
-        }
-        if (!foundFrag) {
-          foundFrag = findFragmentByPTS(
-            fragPrevious,
-            fragments,
-            targetBufferTime,
-            maxFragLookUpTolerance
-          );
+          if (!foundFrag) {
+            foundFrag = findFragmentByPTS(
+              fragPrevious,
+              fragments,
+              targetBufferTime,
+              maxFragLookUpTolerance
+            );
+            if (!foundFrag && fragPrevious.start < fragments[0].start) {
+              foundFrag = fragments[0];
+            }
+          }
         }
       } else {
         foundFrag = fragments[fragLen - 1];

diff --git a/tests/unit/controller/fragment-finders.js b/tests/unit/controller/fragment-finders.js
@@ -106,6 +106,52 @@ describe('Fragment finders', function () {
       findFragmentByPTS(fragments[0], fragments, bufferEnd, tolerance);
       expect(binarySearchSpy).to.have.been.calledOnce;
     });
+
+    it('returns null when there is a gap in sn and start-end time', function () {
+      const bufferEnd = 49;
+      const fragments = [
+        {
+          deltaPTS: 0,
+          cc: 0,
+          duration: 5,
+          start: 54,
+          sn: 5,
+          level: 0,
+        },
+        {
+          deltaPTS: 0,
+          cc: 0,
+          duration: 5,
+          start: 59,
+          sn: 5,
+          level: 0,
+        },
+        {
+          deltaPTS: 0,
+          cc: 0,
+          duration: 5,
+          start: 64,
+          sn: 5,
+          level: 0,
+        },
+      ];
+      // sn is not contiguous, and there is a gap between start and end
+      const fragPrevious = {
+        deltaPTS: 0,
+        cc: 0,
+        duration: 5,
+        start: 44,
+        sn: 1,
+        level: 0,
+      };
+      const actual = findFragmentByPTS(
+        fragPrevious,
+        fragments,
+        bufferEnd,
+        tolerance
+      );
+      expect(actual).to.equal(null);
+    });
   });
 
   describe('fragmentWithinToleranceTest', function () {