Tracking de l'application VApp (IHM du jeu)

VApp/node_modules/mux.js/lib/mp4/webvtt-parser.js

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+const { parseTfdt } = require("../tools/mp4-inspector");
+const findBox = require("./find-box");
+const { getTimescaleFromMediaHeader } = require("./probe");
+const { parseSamples, getMdatTrafPairs } = require("./samples");
+
+/**
+ * Module for parsing WebVTT text and styles from FMP4 segments.
+ * Based on the ISO/IEC 14496-30.
+ */
+const WebVttParser = function() {
+  // default timescale to 90k
+  let timescale = 90e3;
+
+  /**
+   * Parses the timescale from the init segment.
+   * @param {Array<Uint8Array>} segment The initialization segment to parse the timescale from.
+   */
+  this.init = function(segment) {
+    // We just need the timescale from the init segment.
+    const mdhd = findBox(segment, ['moov', 'trak', 'mdia', 'mdhd'])[0];
+
+    if (mdhd) {
+      timescale = getTimescaleFromMediaHeader(mdhd);
+    }
+  };
+
+  /**
+   * Parses a WebVTT FMP4 segment.
+   * @param {Array<Uint8Array>} segment The content segment to parse the WebVTT cues from.
+   * @returns The WebVTT cue text, styling, and timing info as an array of cue objects.
+   */
+  this.parseSegment = function(segment) {
+    const vttCues = [];
+    const mdatTrafPairs = getMdatTrafPairs(segment);
+    let baseMediaDecodeTime = 0;
+
+    mdatTrafPairs.forEach(function(pair) {
+      const mdatBox = pair.mdat;
+      const trafBox = pair.traf;
+      // zero or one.
+      const tfdtBox = findBox(trafBox, ['tfdt'])[0];
+      // zero or one.
+      const tfhdBox = findBox(trafBox, ['tfhd'])[0];
+      // zero or more.
+      const trunBoxes = findBox(trafBox, ['trun']);
+  
+      if (tfdtBox) {
+        const tfdt = parseTfdt(tfdtBox);
+  
+        baseMediaDecodeTime = tfdt.baseMediaDecodeTime;
+      }
+
+      if (trunBoxes.length && tfhdBox) {
+        const samples = parseSamples(trunBoxes, baseMediaDecodeTime, tfhdBox);
+        let mdatOffset = 0;
+
+        samples.forEach(function(sample) {
+          // decode utf8 payload
+          const UTF_8 = 'utf-8';
+          const textDecoder = new TextDecoder(UTF_8);
+          // extract sample data from the mdat box.
+          // WebVTT Sample format:
+          // Exactly one VTTEmptyCueBox box
+          // OR one or more VTTCueBox boxes.
+          const sampleData = mdatBox.slice(mdatOffset, mdatOffset + sample.size);
+          // single vtte box.
+          const vtteBox = findBox(sampleData, ['vtte'])[0];
+
+          // empty box
+          if (vtteBox) {
+            mdatOffset += sample.size;
+            return;
+          }
+
+          // TODO: Support 'vtta' boxes.
+          // VTTAdditionalTextBoxes can be interleaved between VTTCueBoxes.
+
+          const vttcBoxes = findBox(sampleData, ['vttc']);
+
+          vttcBoxes.forEach(function(vttcBox) {
+            // mandatory payload box.
+            const paylBox = findBox(vttcBox, ['payl'])[0];
+            // optional settings box
+            const sttgBox = findBox(vttcBox, ['sttg'])[0];
+            const start = sample.pts / timescale;
+            const end = (sample.pts + sample.duration) / timescale;
+            let cueText, settings;
+
+            // contains cue text.
+            if (paylBox) {
+              try {
+                cueText = textDecoder.decode(paylBox);
+              } catch(e) {
+                console.error(e);
+              }
+            }
+
+            // settings box contains styling.
+            if (sttgBox) {
+              try {
+                settings = textDecoder.decode(sttgBox);
+              } catch(e) {
+                console.error(e);
+              }
+            }
+
+            if (sample.duration && cueText) {
+              vttCues.push({
+                cueText,
+                start,
+                end,
+                settings
+              });
+            }
+          });
+
+          mdatOffset += sample.size;
+        });
+      }
+    });
+
+    return vttCues;
+  };
+};
+
+module.exports = WebVttParser;