feat: Parses a TFDT Box, with a loss of precision beyond 53 bits (sha…

…ka-project#5329)
theodab · Jun 21, 2023 · db73e1f · db73e1f
1 parent 9e6655a
commit db73e1f
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Showing 2 changed files with 25 additions and 4 deletions.
diff --git a/lib/media/media_source_engine.js b/lib/media/media_source_engine.js
@@ -688,11 +688,9 @@ shaka.media.MediaSourceEngine = class {
               goog.asserts.assert(
                   box.version == 0 || box.version == 1,
                   'TFDT version can only be 0 or 1');
-
-              const parsedTFDTBox = shaka.util.Mp4BoxParsers.parseTFDT(
+              const parsed = shaka.util.Mp4BoxParsers.parseTFDTInaccurate(
                   box.reader, box.version);
-              const baseTime = parsedTFDTBox.baseMediaDecodeTime;
-              startTime = baseTime / timescale;
+              startTime = parsed.baseMediaDecodeTime / timescale;
               parsedMedia = true;
               box.parser.stop();
             }).parse(data, /* partialOkay= */ true);

diff --git a/lib/util/mp4_box_parsers.js b/lib/util/mp4_box_parsers.js
@@ -66,6 +66,29 @@ shaka.util.Mp4BoxParsers = class {
     };
   }
 
+  /**
+   * Parses a TFDT Box, with a loss of precision beyond 53 bits.
+   * Use only when exact integers are not required, e.g. when
+   * dividing by the timescale.
+   *
+   * @param {!shaka.util.DataViewReader} reader
+   * @param {number} version
+   * @return {!shaka.util.ParsedTFDTBox}
+   */
+  static parseTFDTInaccurate(reader, version) {
+    if (version == 1) {
+      const high = reader.readUint32();
+      const low = reader.readUint32();
+      return {
+        baseMediaDecodeTime: (high * Math.pow(2, 32)) + low,
+      };
+    } else {
+      return {
+        baseMediaDecodeTime: reader.readUint32(),
+      };
+    }
+  }
+
   /**
    * Parses a MDHD Box.
    * @param {!shaka.util.DataViewReader} reader