static headerSize(box) {
    const basicHeaderSize = 8;
    const _64BitFieldSize = box.has64BitSize ? 8 : 0;
    const versionAndFlagsSize = box.flags != null ? 4 : 0;
    return basicHeaderSize + _64BitFieldSize + versionAndFlagsSize;
  }
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