函数 av_log_set_callback 

pub unsafe extern "C" fn av_log_set_callback(
    callback: Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: c_int, arg3: *const c_char, arg4: va_list)>,
)

Set the logging callback

@note The callback must be thread safe, even if the application does not use threads itself as some codecs are multithreaded.

@see av_log_default_callback

@param callback A logging function with a compatible signature.