函数 av_opt_set_dict_val 

pub unsafe extern "C" fn av_opt_set_dict_val(
    obj: *mut c_void,
    name: *const c_char,
    val: *const AVDictionary,
    search_flags: c_int,
) -> c_int

@note Any old dictionary present is discarded and replaced with a copy of the new one. The caller still owns val is and responsible for freeing it.