fix: Fix header sizes for MP4 boxes with 64-bit size fields

The MP4 box header depends on both whether the box is a "full" box
(with version and flags) and whether the box has an extra 64-bit size
field.  The MP4 parser was only considering the version and flags, but
not whether the extra size field was present.  We already correctly
parsed the 64-bit size field, but computed offsets for other fields
without considering this.

Groundwork for a fix for #2759

Change-Id: I48f16ef073a036954b6f7d25641ccf29828b02c8

Author: joeyparrish

externs/shaka/mp4_parser.js

@@ -17,7 +17,8 @@
  *    size: number,
  *    version: ?number,
  *    flags: ?number,
- *    reader: !shaka.util.DataViewReader
+ *    reader: !shaka.util.DataViewReader,
+ *    has64BitSize: boolean
  * }}
  *
  * @property {!shaka.util.Mp4Parser} parser
@@ -41,6 +42,9 @@
  * @property {!shaka.util.DataViewReader} reader
  *   The reader for this box is only for this box. Reading or not reading to
  *   the end will have no affect on the parser reading other sibling boxes.
+ * @property {boolean} has64BitSize
+ *   If true, the box header had a 64-bit size field.  This affects the offsets
+ *   of other fields.
  * @exportDoc
  */
 shaka.extern.ParsedBox;

lib/util/mp4_parser.js

@@ -114,6 +114,7 @@ shaka.util.Mp4Parser = class {
     let size = reader.readUint32();
     const type = reader.readUint32();
     const name = shaka.util.Mp4Parser.typeToString(type);
+    let has64BitSize = false;
     shaka.log.v2('Parsing MP4 box', name);
 
     switch (size) {
@@ -122,6 +123,7 @@ shaka.util.Mp4Parser = class {
         break;
       case 1:
         size = reader.readUint64();
+        has64BitSize = true;
         break;
     }
 
@@ -160,11 +162,12 @@ shaka.util.Mp4Parser = class {
       const box = {
         parser: this,
         partialOkay: partialOkay || false,
-        version: version,
-        flags: flags,
+        version,
+        flags,
         reader: payloadReader,
-        size: size,
+        size,
         start: start + absStart,
+        has64BitSize,
       };
 
       boxDefinition(box);
@@ -190,11 +193,10 @@ shaka.util.Mp4Parser = class {
    */
   static children(box) {
     // The "reader" starts at the payload, so we need to add the header to the
-    // start position.  This is either 8 or 12 bytes depending on whether this
-    // is a full box.
-    const header = box.flags != null ? 12 : 8;
+    // start position.  The header size varies.
+    const headerSize = shaka.util.Mp4Parser.headerSize(box);
     while (box.reader.hasMoreData() && !box.parser.done_) {
-      box.parser.parseNext(box.start + header, box.reader, box.partialOkay);
+      box.parser.parseNext(box.start + headerSize, box.reader, box.partialOkay);
     }
   }
 
@@ -210,13 +212,12 @@ shaka.util.Mp4Parser = class {
    */
   static sampleDescription(box) {
     // The "reader" starts at the payload, so we need to add the header to the
-    // start position.  This is either 8 or 12 bytes depending on whether this
-    // is a full box.
-    const header = box.flags != null ? 12 : 8;
+    // start position.  The header size varies.
+    const headerSize = shaka.util.Mp4Parser.headerSize(box);
     const count = box.reader.readUint32();
     for (const _ of shaka.util.Iterables.range(count)) {
       shaka.util.Functional.ignored(_);
-      box.parser.parseNext(box.start + header, box.reader, box.partialOkay);
+      box.parser.parseNext(box.start + headerSize, box.reader, box.partialOkay);
       if (box.parser.done_) {
         break;
       }
@@ -277,6 +278,20 @@ shaka.util.Mp4Parser = class {
         type & 0xff);
     return name;
   }
+
+  /**
+   * Find the header size of the box.
+   * Useful for modifying boxes in place or finding the exact offset of a field.
+   *
+   * @param {shaka.extern.ParsedBox} box
+   * @return {number}
+   * @export
+   */
+  static headerSize(box) {
+    return /* basic header */ 8
+        + /* additional 64-bit size field */ (box.has64BitSize ? 8 : 0)
+        + /* version and flags for a "full" box */ (box.flags != null ? 4 : 0);
+  }
 };