png: Support RGBA64 pixel format

libavcodec/pngdec.c

@@ -520,6 +520,9 @@ static int decode_frame(AVCodecContext *avctx,
                 } else if (s->bit_depth == 16 &&
                            s->color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
                     avctx->pix_fmt = AV_PIX_FMT_YA16BE;
+                } else if (s->bit_depth == 16 &&
+                           s->color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
+                    avctx->pix_fmt = AV_PIX_FMT_RGBA64BE;
                 } else {
                     avpriv_report_missing_feature(avctx,
                                                   "Bit depth %d color type %d",