Tracking de l'application VApp (IHM du jeu)

VApp/node_modules/mux.js/lib/mp4/emsg.js

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+var uint8ToCString = require('../utils/string.js').uint8ToCString;
+var getUint64 = require('../utils/numbers.js').getUint64;
+
+/**
+ * Based on: ISO/IEC 23009 Section: 5.10.3.3
+ * References:
+ * https://dashif-documents.azurewebsites.net/Events/master/event.html#emsg-format
+ * https://aomediacodec.github.io/id3-emsg/
+ * 
+ * Takes emsg box data as a uint8 array and returns a emsg box object
+ * @param {UInt8Array} boxData data from emsg box
+ * @returns A parsed emsg box object
+ */
+var parseEmsgBox = function(boxData) {
+  // version + flags
+  var offset = 4;
+  var version = boxData[0];
+  var scheme_id_uri, 
+    value, 
+    timescale, 
+    presentation_time, 
+    presentation_time_delta, 
+    event_duration, 
+    id,
+    message_data;
+  if (version === 0) {
+    scheme_id_uri = uint8ToCString(boxData.subarray(offset));
+    offset += scheme_id_uri.length;
+    value = uint8ToCString(boxData.subarray(offset));
+    offset += value.length;
+    var dv = new DataView(boxData.buffer);
+    timescale = dv.getUint32(offset);
+    offset += 4;
+    presentation_time_delta = dv.getUint32(offset);
+    offset += 4;
+    event_duration = dv.getUint32(offset);
+    offset += 4;
+    id = dv.getUint32(offset);
+    offset += 4;
+  } else if (version === 1) {
+    var dv = new DataView(boxData.buffer);
+    timescale = dv.getUint32(offset);
+    offset += 4;
+    presentation_time = getUint64(boxData.subarray(offset));
+    offset += 8;
+    event_duration = dv.getUint32(offset);
+    offset += 4;
+    id = dv.getUint32(offset);
+    offset += 4;
+    scheme_id_uri = uint8ToCString(boxData.subarray(offset));
+    offset += scheme_id_uri.length;
+    value = uint8ToCString(boxData.subarray(offset));
+    offset += value.length;        
+  }
+
+  message_data = new Uint8Array(boxData.subarray(offset, boxData.byteLength));
+  var emsgBox = {
+    scheme_id_uri, 
+    value,
+    // if timescale is undefined or 0 set to 1 
+    timescale: timescale ? timescale : 1, 
+    presentation_time, 
+    presentation_time_delta, 
+    event_duration, 
+    id,
+    message_data };
+
+  return isValidEmsgBox(version, emsgBox) ? emsgBox : undefined;
+};
+
+/**
+ * Scales a presentation time or time delta with an offset with a provided timescale
+ * @param {number} presentationTime 
+ * @param {number} timescale 
+ * @param {number} timeDelta 
+ * @param {number} offset 
+ * @returns the scaled time as a number
+ */
+var scaleTime = function(presentationTime, timescale, timeDelta, offset) {
+  return presentationTime || presentationTime === 0 ? presentationTime / timescale : offset + timeDelta / timescale;
+};
+
+/**
+ * Checks the emsg box data for validity based on the version
+ * @param {number} version of the emsg box to validate
+ * @param {Object} emsg the emsg data to validate
+ * @returns if the box is valid as a boolean
+ */
+var isValidEmsgBox = function(version, emsg) {
+  var hasScheme = emsg.scheme_id_uri !== '\0'
+  var isValidV0Box = version === 0 && isDefined(emsg.presentation_time_delta) && hasScheme;
+  var isValidV1Box = version === 1 && isDefined(emsg.presentation_time) && hasScheme;
+  // Only valid versions of emsg are 0 and 1
+  return !(version > 1) && isValidV0Box || isValidV1Box;
+};
+
+// Utility function to check if an object is defined
+var isDefined = function(data) {
+  return data !== undefined || data !== null;
+};
+
+module.exports = { 
+  parseEmsgBox: parseEmsgBox, 
+  scaleTime: scaleTime
+};