iphone - Extract iPod Library raw PCM samples and play with sound effects -

i trying extract raw pcm samples mp3 in ipod library can play song , manipulate pitch, tempo, , apply sound effects (such filters). have gone down route of avplayer , avaudioplayer both not allow control on playback @ all.

the code below far have gotten this. @ point not know cmsamplebufferref's in while loop because not know framework use in order playback audio , apply such effects.

any idea best approach achieve this? have looked @ cases file converted using avassetwriter not going cut me because process time consuming. surely can read pcm samples memory playback without having write them disk first?

nb: know code below references mp3 within project aware approach work same if pulling nsurl mpmediapropertyasseturl

  -(ibaction)loadtrack:(id)sender {   nsstring *songpath = [[nsbundle mainbundle] pathforresource:@"smooth_sub focus_192" oftype:@"mp3"];  nsurl *asseturl = [[nsurl alloc] initfileurlwithpath:songpath];   avurlasset *songasset = [avurlasset urlassetwithurl:asseturl options:nil];   nserror *asseterror = nil;  avassetreader *assetreader = [[avassetreader assetreaderwithasset:songasset                 error:&asseterror] retain];  if (asseterror) {   nslog (@"error: %@", asseterror);   return;  }   avassetreaderoutput *assetreaderoutput = [[avassetreaderaudiomixoutput assetreaderaudiomixoutputwithaudiotracks:songasset.tracks                            audiosettings: nil] retain];  if (![assetreader canaddoutput:assetreaderoutput]) {   nslog (@"incompatible asser reader output");   return;  }   [assetreader addoutput: assetreaderoutput];  [assetreader startreading];   cmsamplebufferref nextbuffer;  while (nextbuffer = [assetreaderoutput copynextsamplebuffer]) {   /* do here? */  }   [assetreader release];  [assetreaderoutput release];  }  

i'm doing similar in own code. following method returns nsdata avurlasset:

- (nsdata *)extractdataforasset:(avurlasset *)songasset {      nserror * error = nil;     avassetreader * reader = [[avassetreader alloc] initwithasset:songasset error:&error];      avassettrack * songtrack = [songasset.tracks objectatindex:0];     avassetreadertrackoutput * output = [[avassetreadertrackoutput alloc] initwithtrack:songtrack outputsettings:nil];     [reader addoutput:output];     [output release];      nsmutabledata * fullsongdata = [[nsmutabledata alloc] init];     [reader startreading];      while (reader.status == avassetreaderstatusreading){          avassetreadertrackoutput * trackoutput = (avassetreadertrackoutput *)[reader.outputs objectatindex:0];         cmsamplebufferref samplebufferref = [trackoutput copynextsamplebuffer];          if (samplebufferref){             cmblockbufferref blockbufferref = cmsamplebuffergetdatabuffer(samplebufferref);              size_t length = cmblockbuffergetdatalength(blockbufferref);             uint8 buffer[length];             cmblockbuffercopydatabytes(blockbufferref, 0, length, buffer);              nsdata * data = [[nsdata alloc] initwithbytes:buffer length:length];             [fullsongdata appenddata:data];             [data release];              cmsamplebufferinvalidate(samplebufferref);             cfrelease(samplebufferref);         }     }      if (reader.status == avassetreaderstatusfailed || reader.status == avassetreaderstatusunknown){         // went wrong. handle it.     }      if (reader.status == avassetreaderstatuscompleted){         // you're done. worked.     }      [reader release];      return [fullsongdata autorelease]; } 

i recommend doing on background thread because it's time consuming.

a drawback method whole song loaded memory, of course limited.