static sampleDescription(box) {
    // The "reader" starts at the payload, so we need to add the header to the
    // start position.  The header size varies.
    const headerSize = shaka.util.Mp4Parser.headerSize(box);
    const count = box.reader.readUint32();
    for (let i = 0; i < count; i++) {
      box.parser.parseNext(box.start + headerSize, box.reader, box.partialOkay);
      if (box.parser.done_) {
        break;
      }
    }
  }
A callback that tells the Mp4 parser to treat the body of a box as a sample
description. A sample description box has a fixed number of children. The
number of children is represented by a 4 byte unsigned integer. Each child
is a box.

@param {!shaka.extern.ParsedBox} box
@export