multi track mp3 playback for iOS application

Question

I am doing an application that involves playing back a song in a multi track format (drums, vocals, guitar, piano, etc...). I don't need to do any fancy audio processing to each track, all I need to be able to do is play, pause, and mute/unmute each track.

I had been using multiple instances of AVAudioPlayer but when performing device testing, I noticed that the tracks are playing very slightly out of sync when they are first played. Furthermore, when I pause and play the tracks they continue to get more out of sync. After a bit of research I've realized that AVAudioplayer just has too much latency and won't work for my application.

In my application I basically had an NSArray of AVAudioPlayers that I would loop through and play each one or pause/stop each one, I'm sure this is what caused it to get out of sync on the device.

It seemed like apple's audio mixer would work well for me, but when I try implementing it I get a EXC_BAD_ACCESS error that I can't figure out.

I know the answer is to use OpenAL or audio units but It just seems unnecessary to spend weeks learning about these when all I need to do is play around 5 .mp3 tracks at the same time. Does anyone have any suggestions on how to accomplish this? Thanks

Answer 1

thanks to admsyn's suggestion I was able to come up with a solution.

AVAudioPlayer has a currentTime property that returns the current time of a track and can also be set.

So I implemented the startSynchronizedPlayback as stated by admsyn and then added the following when I stopped the tracks:

-(void) stopAll
{
int count = [tracksArr count];
for(int i = 0; i < count; i++)
    {
    trackModel = [tracksArr objectAtIndex:i]
    if(i = 0)
        {
         currentTime = [trackModel currentTime]
        }
    [trackModel stop]
    [trackModel setCurrentTime:currentTime]
    }
{

This code basically loops through my array of tracks which each hold their own AVAudioPlayer, grabs the current time from the first track, then sets all of the following tracks to that time. Now when I use the startSynchronizedPlayback method they all play in sync, and pausing unpausing keeps them in sync as well. Hope this is helpful to someone else trying to keep tracks in sync.