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playback in the background

Oct 22, 2009 at 2:04 PM


we are developing a wpf application and we are trying (quite successfully so far, thanks for the great work!) to use NAudio to play an mp3 while the app is working (as a background melody). the main idea is the sound not to stop while the dispatcher (UI) thread is busy doing something and the playback to be controllable (i.e. play/stop/play). First we tried with DirectSoundOut as a playback device as it is doing its sound processing/playback in a background thread (digging into the code we saw that it spawns a thread) and indeed using it there are no problems of playback stopping if the dispatcher thread is busy. But there were all kinds of other weird behaviour and crashes when controlling the playback with play() and stop(), to sum up DirectSoundOut was rather unstable. So we tried WaveOut which turned out to be more stable (no crashes with start()/stop()). Now the question is how to make it play in a background thread and control it? Does the device need to be created in a background thread or only the play() method called on a background thread? Help would be much appreciated, thanks !

Oct 22, 2009 at 2:07 PM

Hi Xenry,

What version of NAudio are you using, and what constructor of WaveOut? There is a function callback option. The only trouble with this is that some audio chipsets don't play nice with the function callback. I'm sorry you ran into problems with DirectSoundOut. That code hasn't been exercised very heavily, so maybe needs a bit more robustness work. Do you have any stack traces of your crashes?



Oct 22, 2009 at 4:06 PM
Edited Oct 22, 2009 at 4:08 PM

thanks for the quick reply, Mark

the version is

some more words about the situation we are getting the crashes. the app should play videos (its kind of multimedia app) and the trick is that when the user starts a video, the background sound should be stopped and when the video finishes (is stopped) the background sound should start playing again. now from time to time (actually quite often) when the sound is stopped ( DirectSoundOut.Stop() ) the audio kind of plays only the last buffer (i.e. repeats one pattern) but does not stop and the strange thing is that wpf's MediaElement refuses to play videos any more and DirectSoundOut.Play() does not seem to work any more (the audio pattern keeps repeating till the app is closed). maybe the problem is somewhere in the windows itself (xp sp3 here) or the MediaElement or sth else, its strange but that does not happen (at least has not happened so far) with WaveOut. the stack trace looks sth like:

about WaveOut we tried both WaveOut() and 

vahwnd = new WindowInteropHelper(Application.Current.MainWindow).Handle;
            mPlaybackDevice = new WaveOut(hwnd)
var hwnd = new WindowInteropHelper(Application.Current.MainWindow).Handle;
mPlaybackDevice = new WaveOut(hwnd);

both worked, but just cannot figure out how to start playback in a different thread. for instance 

ThreadPool.QueueUserWorkItem(delegate(object state) {
does not seem to make any difference. Thanks again !
Oct 22, 2009 at 4:21 PM

Hi xenry

you should be able to run with window callbacks on a background thread so long as you create a (hidden) window and get it pumping messages (that's the tricky part).

Also have you tried new WaveOut(WaveCallbackInfo.FunctionCallback())      

I didn't write the DirectSoundOut code myself (just did a bit of threading work on it), so I will need to familiarise myself with what the IsBufferLost is doing.

I should also ask why you aren't just using WPF MediaElement to play your MP3. Might be easier?



Oct 22, 2009 at 4:31 PM

thanks, will try with hidden window and see if I can get it working. we headed to NAudio because the mp3-s should be played from memorystream and not extracted to hdd :/ and MediaElement also had problems with some kinds of mp3s