Account for overlapping sidx subsegment durations by parsing earlierstPresentationTime

src/utils/mp4-tools.ts

@@ -38,6 +38,13 @@
   return val < 0 ? 4294967296 + val : val;
 }
 
+export function readUint64(buffer: Uint8Array, offset: number) {
+  let result = readUint32(buffer, offset);
+  result *= Math.pow(2, 32);
+  result += readUint32(buffer, offset + 4);
+  return result;
+}
+
 export function readSint32(buffer: Uint8Array, offset: number): number {
   return (
     (buffer[offset] << 24) |
@@ -125,15 +132,15 @@
   const timescale = readUint32(sidx, index);
   index += 4;
 
-  // TODO: parse earliestPresentationTime and firstOffset
-  // usually zero in our case
-  const earliestPresentationTime = 0;
-  const firstOffset = 0;
+  let earliestPresentationTime = 0;
+  let firstOffset = 0;
 
   if (version === 0) {
-    index += 8;
+    earliestPresentationTime = readUint32(sidx, (index += 4));
+    firstOffset = readUint32(sidx, (index += 4));
   } else {
-    index += 16;
+    earliestPresentationTime = readUint64(sidx, (index += 8));
+    firstOffset = readUint64(sidx, (index += 8));
   }
 
   // skip reserved
@@ -469,7 +476,7 @@
 
 function skipBERInteger(bytes: Uint8Array, i: number): number {
   const limit = i + 5;
   while (bytes[i++] & 0x80 && i < limit) {}
   return i;
 }
 
@@ -677,19 +684,31 @@
   }
   if (videoDuration === 0 && audioDuration === 0) {
     // If duration samples are not available in the traf use sidx subsegment_duration
+    let sidxMinStart = Infinity;
+    let sidxMaxEnd = 0;
     let sidxDuration = 0;
     const sidxs = findBox(data, ['sidx']);
     for (let i = 0; i < sidxs.length; i++) {
       const sidx = parseSegmentIndex(sidxs[i]);
       if (sidx?.references) {
-        sidxDuration += sidx.references.reduce(
+        sidxMinStart = Math.min(
+          sidxMinStart,
+          sidx.earliestPresentationTime / sidx.timescale,
+        );
+        const subSegmentDuration = sidx.references.reduce(
           (dur, ref) => dur + ref.info.duration || 0,
           0,
         );
+        sidxMaxEnd = Math.max(
+          sidxMaxEnd,
+          subSegmentDuration + sidx.earliestPresentationTime / sidx.timescale,
+        );
+        sidxDuration = sidxMaxEnd - sidxMinStart;
       }
     }
-
-    return sidxDuration;
+    if (sidxDuration && Number.isFinite(sidxDuration)) {
+      return sidxDuration;
+    }
   }
   if (videoDuration) {
     return videoDuration;