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

…ka-project#5354)
theodab · Jun 26, 2023 · a797651 · a797651
1 parent ebaddf0
commit a797651
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Showing 3 changed files with 52 additions and 42 deletions.
diff --git a/lib/media/streaming_engine.js b/lib/media/streaming_engine.js
@@ -2038,30 +2038,16 @@ shaka.media.StreamingEngine = class {
       !reference.initSegmentReference.timescale) {
       return;
     }
-    box.reader.readUint32(); // Ignore referenceTrackId
-    const ntpTimestampSec = box.reader.readUint32();
-    const ntpTimestampFrac = box.reader.readUint32();
-    const ntpTimestamp = ntpTimestampSec * 1000 +
-        ntpTimestampFrac / 2**32 * 1000;
-
-    let mediaTime;
-    if (box.version === 0) {
-      mediaTime = box.reader.readUint32();
-    } else {
-      try {
-        mediaTime = box.reader.readUint64();
-      } catch (e) {
-        shaka.log.warning('parsePrft_: parsing mediatime resulted in a '+
-          'MEDIA.JS_INTEGER_OVERFLOW exception');
-        this.parsedPrftEventRaised_ = true;
-        return;
-      }
-    }
+    goog.asserts.assert(
+        box.version == 0 || box.version == 1,
+        'PRFT version can only be 0 or 1');
+    const parsed = shaka.util.Mp4BoxParsers.parsePRFTInaccurate(
+        box.reader, box.version);
 
     const timescale = reference.initSegmentReference.timescale;
-    const wallClockTime = this.convertNtp(ntpTimestamp);
+    const wallClockTime = this.convertNtp(parsed.ntpTimestamp);
     const programStartDate = new Date(wallClockTime -
-      (mediaTime / timescale) * 1000);
+      (parsed.mediaTime / timescale) * 1000);
     const prftInfo = {
       wallClockTime,
       programStartDate,
@@ -2077,11 +2063,11 @@ shaka.media.StreamingEngine = class {
 
 
   /**
-     * Convert Ntp ntpTimeStamp to UTC Time
-     *
-     * @param {number} ntpTimeStamp
-     * @return {number} utcTime
-     */
+   * Convert Ntp ntpTimeStamp to UTC Time
+   *
+   * @param {number} ntpTimeStamp
+   * @return {number} utcTime
+   */
   convertNtp(ntpTimeStamp) {
     const start = new Date(Date.UTC(1900, 0, 1, 0, 0, 0));
     return new Date(start.getTime() + ntpTimeStamp).getTime();

diff --git a/lib/util/mp4_box_parsers.js b/lib/util/mp4_box_parsers.js
@@ -89,6 +89,36 @@ shaka.util.Mp4BoxParsers = class {
     }
   }
 
+  /**
+   * Parses a PRFT 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.ParsedPRFTBox}
+   */
+  static parsePRFTInaccurate(reader, version) {
+    reader.readUint32(); // Ignore referenceTrackId
+    const ntpTimestampSec = reader.readUint32();
+    const ntpTimestampFrac = reader.readUint32();
+    const ntpTimestamp = ntpTimestampSec * 1000 +
+        ntpTimestampFrac / 2**32 * 1000;
+
+    let mediaTime;
+    if (version === 0) {
+      mediaTime = reader.readUint32();
+    } else {
+      const high = reader.readUint32();
+      const low = reader.readUint32();
+      mediaTime = (high * Math.pow(2, 32)) + low;
+    }
+    return {
+      mediaTime,
+      ntpTimestamp,
+    };
+  }
+
   /**
    * Parses a MDHD Box.
    * @param {!shaka.util.DataViewReader} reader
@@ -332,6 +362,16 @@ shaka.util.ParsedTFHDBox;
  */
 shaka.util.ParsedTFDTBox;
 
+/**
+ * @typedef {{
+ *    mediaTime: number,
+ *    ntpTimestamp: number
+ * }}
+ *
+ * @exportDoc
+ */
+shaka.util.ParsedPRFTBox;
+
 /**
  * @typedef {{
  *    timescale: number,

diff --git a/test/media/streaming_engine_unit.js b/test/media/streaming_engine_unit.js
@@ -3226,22 +3226,6 @@ describe('StreamingEngine', () => {
           expectedStartDate.toUTCString());
     });
 
-    it('does not raise event if mediatime exceeds Number.MAX_VALUE',
-        async () => {
-          const prftSegment = Uint8ArrayUtils.fromHex(
-              '00000020707266740100000000000001E683B62E8E63CC58'+
-                                              'FFFFFFFFFFFFFFFF');
-          segmentData[ContentType.VIDEO].segments[0] = prftSegment;
-          segmentData[ContentType.VIDEO].initSegments[0] = mdhdSegment;
-
-          streamingEngine.switchVariant(variant);
-          streamingEngine.switchTextStream(textStream);
-          await streamingEngine.start();
-          playing = true;
-          await runTest();
-          expect(onEvent).not.toHaveBeenCalled();
-        });
-
     it('raises an event once only', async () => {
       segmentData[ContentType.VIDEO].segments[0] =
           shaka.util.Uint8ArrayUtils.concat(prftSegment, prftSegment);