函数 av_opt_is_set_to_default_by_name 

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

Check if given option is set to its default value.

@param obj AVClass object to check option on @param name option name @param search_flags combination of AV_OPT_SEARCH_* @return >0 when option is set to its default, 0 when option is not set its default, <0 on error