What is the standard of appeal on appeal against a finding that a witness was unavailable?

We apply the following standard on an appeal challenging a trial court's ruling that a witness was unavailable: "We review the trial court's resolution of disputed factual issues under the differential substantial evidence standard . . . , and independently review whether the facts demonstrate prosecutorial good faith and due diligence . . . ." (Herrera, supra, 49 Cal.4th at p. 623.) Finally, when it is determined on appeal that a witness's testimony was wrongly admitted in violation of constitutional confrontation protections, the error is subject to a harmless error analysis under the standard articulated in Chapman v. California (1967) 386 U.S. 18, 24. (People v. Ledesma (2006) 39 Cal.4th 641, 709.)