+int av_opt_get_image_size(void *obj, const char *name, int search_flags, int *w_out, int *h_out);
+int av_opt_get_pixel_fmt (void *obj, const char *name, int search_flags, enum AVPixelFormat *out_fmt);
+int av_opt_get_sample_fmt(void *obj, const char *name, int search_flags, enum AVSampleFormat *out_fmt);