Eagerly match segments without tolerance offset (video-dev#5084)

* Eagerly match segments without tolerance offset
Fixes video-dev#4919

* Maintain expected `fragPrevious` behavior

src/controller/fragment-finders.ts

@@ -82,7 +82,7 @@ export function findFragmentByPTS(
     fragments,
     fragmentWithinToleranceTest.bind(null, bufferEnd, maxFragLookUpTolerance)
   );
-  if (foundFragment) {
+  if (foundFragment && (foundFragment !== fragPrevious || !fragNext)) {
     return foundFragment;
   }
   // If no match was found return the next fragment after fragPrevious, or null
@@ -101,6 +101,13 @@ export function fragmentWithinToleranceTest(
   maxFragLookUpTolerance = 0,
   candidate: Fragment
 ) {
+  // eagerly accept an accurate match (no tolerance)
+  if (
+    candidate.start <= bufferEnd &&
+    candidate.start + candidate.duration > bufferEnd
+  ) {
+    return 0;
+  }
   // offset should be within fragment boundary - config.maxFragLookUpTolerance
   // this is to cope with situations like
   // bufferEnd = 9.991

tests/unit/controller/fragment-finders.js

@@ -192,7 +192,7 @@ describe('Fragment finders', function () {
       expect(actual).to.equal(-1);
     });
 
-    it('does not skip very small fragments', function () {
+    it('does not skip very small fragments at the start', function () {
       const frag = {
         start: 0.2,
         duration: 0.1,
@@ -201,6 +201,31 @@ describe('Fragment finders', function () {
       const actual = fragmentWithinToleranceTest(0, tolerance, frag);
       expect(actual).to.equal(0);
     });
+    it('does not skip very small fragments', function () {
+      const frag = {
+        start: 5,
+        duration: 0.1,
+        deltaPTS: 0.1,
+      };
+      const actual = fragmentWithinToleranceTest(5, tolerance, frag);
+      expect(actual).to.equal(0);
+    });
+    it('does not skip very small fragments without deltaPTS', function () {
+      const frag = {
+        start: 5,
+        duration: 0.1,
+      };
+      const actual = fragmentWithinToleranceTest(5, tolerance, frag);
+      expect(actual).to.equal(0);
+    });
+    it('does not skip fragments when searching near boundaries', function () {
+      const frag = {
+        start: 19.96916,
+        duration: 9.98458,
+      };
+      const actual = fragmentWithinToleranceTest(29, 0.25, frag);
+      expect(actual).to.equal(0);
+    });
   });
 
   describe('findFragmentByPDT', function () {