(a) (1) In each case subject to appellate review under this title, the accused may file with the convening authority a statement expressly waiving the right of the accused to such appeal.
(2) Such a waiver shall be signed by both the accused and defense counsel for the accused and shall be filed in accordance with appellate procedures as provided by law.
(b) The accused may withdraw an appeal at any time in accordance with appellate procedures as provided by law.