函数 av_append_path_component 

pub unsafe extern "C" fn av_append_path_component(
    path: *const c_char,
    component: *const c_char,
) -> *mut c_char

Append path component to the existing path. Path separator ‘/’ is placed between when needed. Resulting string have to be freed with av_free(). @param path base path @param component component to be appended @return new path or NULL on error.