static getPsshData(pssh) {
    let offset = 8; // Box size and type fields

    /** @type {!DataView} */
    const view = shaka.util.BufferUtils.toDataView(pssh);

    // Read version
    const version = view.getUint8(offset);

    // Version (1), flags (3), system ID (16)
    offset += 20;

    if (version > 0) {
      // Key ID count (4) and All key IDs (16*count)
      offset += 4 + (16 * view.getUint32(offset));
    }

    // Data size
    offset += 4;

    return shaka.util.BufferUtils.toUint8(view, offset);
  }
Returns just the data portion of a single PSSH

@param {!Uint8Array} pssh
@return {!Uint8Array}