AvAssetReader getting incorrect no of audio samples - ios

Question

I am trying to grab the audio track from a video as raw pcm data. The plan is pass this data into a float* table array in libpd. I have managed to get some sample data but the number of samples reported is way too low. For example for a 29sec clip I am getting a reported 3968 samples. What I am looking forward is the amplitudes at each sample. For a track of audio length of 29 secs I would expect to have an array of 1278900 in size (at 44.1khz).
Here is what I have put together based on other examples:
- (void)audioCapture {
NSLog(#"capturing");
NSError *error;
AVAssetReader* reader = [[AVAssetReader alloc] initWithAsset:self.videoAsset error:&error];
NSArray *audioTracks = [self.videoAsset tracksWithMediaType:AVMediaTypeAudio];
AVAssetTrack *audioTrack = nil;
if ([audioTracks count] > 0)
audioTrack = [audioTracks objectAtIndex:0];
// Decompress to Linear PCM with the asset reader
NSDictionary *decompressionAudioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithUnsignedInt:kAudioFormatLinearPCM], AVFormatIDKey,
nil];
AVAssetReaderOutput *output = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:decompressionAudioSettings];
[reader addOutput:output];
[reader startReading];
CMSampleBufferRef sample = [output copyNextSampleBuffer];
//array for our sample amp values
SInt16* samples = NULL;
//sample count;
CMItemCount numSamplesInBuffer = 0;
//sample buffer
CMBlockBufferRef buffer;
while( sample != NULL )
{
sample = [output copyNextSampleBuffer];
if( sample == NULL )
continue;
buffer = CMSampleBufferGetDataBuffer( sample );
size_t lengthAtOffset;
size_t totalLength;
char* data;
if( CMBlockBufferGetDataPointer( buffer, 0, &lengthAtOffset, &totalLength, &data ) != noErr )
{
NSLog( #"error!" );
break;
}
numSamplesInBuffer = CMSampleBufferGetNumSamples(sample);
AudioBufferList audioBufferList;
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
sample,
NULL,
&audioBufferList,
sizeof(audioBufferList),
NULL,
NULL,
kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
&buffer
);
for (int bufferCount=0; bufferCount < audioBufferList.mNumberBuffers; bufferCount++) {
samples = (SInt16 *)audioBufferList.mBuffers[bufferCount].mData;
NSLog(#"idx %f",(double)samples[bufferCount]);
}
}
NSLog(#"num samps in buf %ld",numSamplesInBuffer);
//[PdBase copyArray:(float *)samples
//toArrayNamed:#"DestTable" withOffset:0
//count:pdTableSize];
}