comments and descriptive var

videojs · Feb 6, 2023 · 1d621d4 · 1d621d4
1 parent 5c8397c
commit 1d621d4
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Showing 2 changed files with 15 additions and 7 deletions.
diff --git a/lib/mp4/probe.js b/lib/mp4/probe.js
@@ -373,16 +373,22 @@ getTracks = function(init) {
 };
 
 /**
- * Returns an array of emsg ID3 data from the provided segmentData
- * ptOffset can also be provided if necessary.
+ * Returns an array of emsg ID3 data from the provided segmentData.
+ * An offset can also be provided as the Latest Arrival Time to calculate 
+ * the Event Start Time of v0 EMSG boxes. 
+ * See: https://dashif-documents.azurewebsites.net/Events/master/event.html#Inband-event-timing
+ * 
+ * @param {Uint8Array} segmentData the segment byte array.
+ * @param {number} offset the segment start time or Latest Arrival Time, 
+ * @return {Object[]} an array of ID3 parsed from EMSG boxes
  */
-getEmsgID3 = function(segmentData, ptOffset = 0) {
+getEmsgID3 = function(segmentData, offset = 0) {
   var emsgBoxes = findBox(segmentData, ['emsg']);
   return emsgBoxes.map((data) => {
     var parsedBox = emsg.parseEmsgBox(new Uint8Array(data));
     var parsedId3Frames = parseId3Frames(parsedBox.message_data);
     return {
-      cueTime: emsg.scaleTime(parsedBox.presentation_time, parsedBox.timescale, parsedBox.presentation_time_delta, ptOffset),
+      cueTime: emsg.scaleTime(parsedBox.presentation_time, parsedBox.timescale, parsedBox.presentation_time_delta, offset),
       duration: emsg.scaleTime(parsedBox.event_duration, parsedBox.timescale),
       frames: parsedId3Frames
     };

diff --git a/lib/tools/parse-id3.js b/lib/tools/parse-id3.js
@@ -173,14 +173,14 @@ var
     }
   };
 
-// TODO add dispatch type parsing
 var parseId3Frames = function(data) {
   var frameSize, frameHeader,
     frameStart = 10,
     tagSize = 0,
     frames = [];
 
-  // if not valid id3 return early.
+  // If we don't have enough data for a header, 10 bytes, 
+  // or 'ID3' in the first 3 bytes this is not a valid ID3 tag.
   if (data.length < 10 ||
     data[0] !== 'I'.charCodeAt(0) ||
     data[1] !== 'D'.charCodeAt(0) ||
@@ -196,7 +196,9 @@ var parseId3Frames = function(data) {
   // ID3 reports the tag size excluding the header but it's more
   // convenient for our comparisons to include it
   tagSize += 10;
-  if (data[5] & 0x40) {
+  // check bit 6 of byte 5 for the extended header flag.
+  var hasExtendedHeader = data[5] & 0x40;
+  if (hasExtendedHeader) {
     // advance the frame start past the extended header
     frameStart += 4; // header size field
     frameStart += parseSyncSafeInteger(data.subarray(10, 14));