iphone - mac - Dibujar forma de onda con AVAssetReader

apple

Question

Leo canción de la biblioteca de iPod utilizando assetUrl (en el código llamado audioUrl). Puedo jugar de muchas maneras, puedo cortarlo, puedo hacer algo de precesión con esto, pero ... Realmente no entiendo qué voy a hacer con esto. CMSampleBufferRef para obtener datos para dibujar la forma de onda! Necesito información sobre los valores pico, ¿cómo puedo conseguirlo de esta (tal vez otra) forma?

    AVAssetTrack * songTrack = [audioUrl.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){/* what I gonna do with this? */}

¡Por favor, ayúdame!

Answer 1

Deberías poder obtener un buffer de audio de tu sampleBuffRef y luego iterar a través de esos valores para construir tu forma de onda:

CMBlockBufferRef buffer = CMSampleBufferGetDataBuffer( sampleBufferRef );
CMItemCount numSamplesInBuffer = CMSampleBufferGetNumSamples(sampleBufferRef);
AudioBufferList audioBufferList;
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
                                                            sampleBufferRef,
                                                            NULL,
                                                            &audioBufferList,
                                                            sizeof(audioBufferList),
                                                            NULL,
                                                            NULL,
                                                                  kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
                                                            &buffer
                                                            );

// this copies your audio out to a temp buffer but you should be able to iterate through this buffer instead
SInt32* readBuffer = (SInt32 *)malloc(numSamplesInBuffer * sizeof(SInt32));
memcpy( readBuffer, audioBufferList.mBuffers[0].mData, numSamplesInBuffer*sizeof(SInt32));

Answer 2

Estaba buscando algo similar y decidí "hacer lo mío". Me doy cuenta de que esta es una publicación anterior, pero en caso de que alguien más esté en busca de esto, aquí está mi solución. es relativamente rápido y sucio y normaliza la imagen a "escala completa". las imágenes que crea son "anchas", es decir, necesita colocarlas en UIScrollView o administrar la pantalla.

esto se basa en algunas respuestas dadas a esta pregunta

Muestra de salida

EDITAR: He agregado una versión logarítmica de los métodos de promediado y renderizado, vea el final de este mensaje para la versión alternativa y los resultados de comparación. Yo personalmente prefiero la versión lineal original, pero he decidido publicarla, en caso de que alguien pueda mejorar el algoritmo utilizado.

Necesitarás estas importaciones:

#import <MediaPlayer/MediaPlayer.h>
#import <AVFoundation/AVFoundation.h>

En primer lugar, un método de representación genérico que toma un puntero a datos de muestra promediados,
y devuelve un UIImage. Tenga en cuenta que estas muestras no son muestras de audio reproducibles.

-(UIImage *) audioImageGraph:(SInt16 *) samples
                normalizeMax:(SInt16) normalizeMax
                 sampleCount:(NSInteger) sampleCount 
                channelCount:(NSInteger) channelCount
                 imageHeight:(float) imageHeight {

    CGSize imageSize = CGSizeMake(sampleCount, imageHeight);
    UIGraphicsBeginImageContext(imageSize);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor);
    CGContextSetAlpha(context,1.0);
    CGRect rect;
    rect.size = imageSize;
    rect.origin.x = 0;
    rect.origin.y = 0;

    CGColorRef leftcolor = [[UIColor whiteColor] CGColor];
    CGColorRef rightcolor = [[UIColor redColor] CGColor];

    CGContextFillRect(context, rect);

    CGContextSetLineWidth(context, 1.0);

    float halfGraphHeight = (imageHeight / 2) / (float) channelCount ;
    float centerLeft = halfGraphHeight;
    float centerRight = (halfGraphHeight*3) ; 
    float sampleAdjustmentFactor = (imageHeight/ (float) channelCount) / (float) normalizeMax;

    for (NSInteger intSample = 0 ; intSample < sampleCount ; intSample ++ ) {
        SInt16 left = *samples++;
        float pixels = (float) left;
        pixels *= sampleAdjustmentFactor;
        CGContextMoveToPoint(context, intSample, centerLeft-pixels);
        CGContextAddLineToPoint(context, intSample, centerLeft+pixels);
        CGContextSetStrokeColorWithColor(context, leftcolor);
        CGContextStrokePath(context);

        if (channelCount==2) {
            SInt16 right = *samples++;
            float pixels = (float) right;
            pixels *= sampleAdjustmentFactor;
            CGContextMoveToPoint(context, intSample, centerRight - pixels);
            CGContextAddLineToPoint(context, intSample, centerRight + pixels);
            CGContextSetStrokeColorWithColor(context, rightcolor);
            CGContextStrokePath(context); 
        }
    }

    // Create new image
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    // Tidy up
    UIGraphicsEndImageContext();   

    return newImage;
}

A continuación, un método que toma un AVURLAsset y devuelve datos de imagen PNG

- (NSData *) renderPNGAudioPictogramForAsset:(AVURLAsset *)songAsset {

    NSError * error = nil;
    AVAssetReader * reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];
    AVAssetTrack * songTrack = [songAsset.tracks objectAtIndex:0];

    NSDictionary* outputSettingsDict = [[NSDictionary alloc] initWithObjectsAndKeys:
                                        [NSNumber numberWithInt:kAudioFormatLinearPCM],AVFormatIDKey,
                                        //     [NSNumber numberWithInt:44100.0],AVSampleRateKey, /*Not Supported*/
                                        //     [NSNumber numberWithInt: 2],AVNumberOfChannelsKey,    /*Not Supported*/
                                        [NSNumber numberWithInt:16],AVLinearPCMBitDepthKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsBigEndianKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsNonInterleaved,
                                        nil];

    AVAssetReaderTrackOutput* output = [[AVAssetReaderTrackOutput alloc] initWithTrack:songTrack outputSettings:outputSettingsDict];

    [reader addOutput:output];
    [output release];

    UInt32 sampleRate,channelCount;

    NSArray* formatDesc = songTrack.formatDescriptions;
    for(unsigned int i = 0; i < [formatDesc count]; ++i) {
        CMAudioFormatDescriptionRef item = (CMAudioFormatDescriptionRef)[formatDesc objectAtIndex:i];
        const AudioStreamBasicDescription* fmtDesc = CMAudioFormatDescriptionGetStreamBasicDescription (item);
        if(fmtDesc ) {

            sampleRate = fmtDesc->mSampleRate;
            channelCount = fmtDesc->mChannelsPerFrame;

            //    NSLog(@"channels:%u, bytes/packet: %u, sampleRate %f",fmtDesc->mChannelsPerFrame, fmtDesc->mBytesPerPacket,fmtDesc->mSampleRate);
        }
    }

    UInt32 bytesPerSample = 2 * channelCount;
    SInt16 normalizeMax = 0;

    NSMutableData * fullSongData = [[NSMutableData alloc] init];
    [reader startReading];

    UInt64 totalBytes = 0;         
    SInt64 totalLeft = 0;
    SInt64 totalRight = 0;
    NSInteger sampleTally = 0;

    NSInteger samplesPerPixel = sampleRate / 50;

    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);
            totalBytes += length;

            NSAutoreleasePool *wader = [[NSAutoreleasePool alloc] init];

            NSMutableData * data = [NSMutableData dataWithLength:length];
            CMBlockBufferCopyDataBytes(blockBufferRef, 0, length, data.mutableBytes);

            SInt16 * samples = (SInt16 *) data.mutableBytes;
            int sampleCount = length / bytesPerSample;
            for (int i = 0; i < sampleCount ; i ++) {

                SInt16 left = *samples++;
                totalLeft  += left;

                SInt16 right;
                if (channelCount==2) {
                    right = *samples++;
                    totalRight += right;
                }

                sampleTally++;

                if (sampleTally > samplesPerPixel) {

                    left  = totalLeft / sampleTally; 

                    SInt16 fix = abs(left);
                    if (fix > normalizeMax) {
                        normalizeMax = fix;
                    }

                    [fullSongData appendBytes:&left length:sizeof(left)];

                    if (channelCount==2) {
                        right = totalRight / sampleTally; 

                        SInt16 fix = abs(right);
                        if (fix > normalizeMax) {
                            normalizeMax = fix;
                        }

                        [fullSongData appendBytes:&right length:sizeof(right)];
                    }

                    totalLeft   = 0;
                    totalRight  = 0;
                    sampleTally = 0;
                }
            }

           [wader drain];

            CMSampleBufferInvalidate(sampleBufferRef);
            CFRelease(sampleBufferRef);
        }
    }

    NSData * finalData = nil;

    if (reader.status == AVAssetReaderStatusFailed || reader.status == AVAssetReaderStatusUnknown){
        // Something went wrong. return nil

        return nil;
    }

    if (reader.status == AVAssetReaderStatusCompleted){

        NSLog(@"rendering output graphics using normalizeMax %d",normalizeMax);

        UIImage *test = [self audioImageGraph:(SInt16 *) 
                         fullSongData.bytes 
                                 normalizeMax:normalizeMax 
                                  sampleCount:fullSongData.length / 4 
                                 channelCount:2
                                  imageHeight:100];

        finalData = imageToData(test);
    }        

    [fullSongData release];
    [reader release];

    return finalData;
}

Opción avanzada: por último, si desea poder reproducir el audio con AVAudioPlayer, deberá almacenarlo en la carpeta de caché de paquete de sus aplicaciones. Como estaba haciendo eso, decidí almacenar en caché también los datos de la imagen, y envolví todo en una categoría de UIImage. necesita incluir esta oferta de código abierto para extraer el audio, y algún código de here para manejar algunas características de enhebrado de fondo.

primero, algunos define, y unos pocos métodos de clase genéricos para manejar nombres de ruta, etc.

//#define imgExt @"jpg"
//#define imageToData(x) UIImageJPEGRepresentation(x,4)

#define imgExt @"png"
#define imageToData(x) UIImagePNGRepresentation(x)

+ (NSString *) assetCacheFolder  {
    NSArray  *assetFolderRoot = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
    return [NSString stringWithFormat:@"%@/audio", [assetFolderRoot objectAtIndex:0]];
 }

+ (NSString *) cachedAudioPictogramPathForMPMediaItem:(MPMediaItem*) item {
    NSString *assetFolder = [[self class] assetCacheFolder];
    NSNumber * libraryId = [item valueForProperty:MPMediaItemPropertyPersistentID];
    NSString *assetPictogramFilename = [NSString stringWithFormat:@"asset_%@.%@",libraryId,imgExt];
    return [NSString stringWithFormat:@"%@/%@", assetFolder, assetPictogramFilename];
}

+ (NSString *) cachedAudioFilepathForMPMediaItem:(MPMediaItem*) item {
    NSString *assetFolder = [[self class] assetCacheFolder];

    NSURL    * assetURL = [item valueForProperty:MPMediaItemPropertyAssetURL];
    NSNumber * libraryId = [item valueForProperty:MPMediaItemPropertyPersistentID];

    NSString *assetFileExt = [[[assetURL path] lastPathComponent] pathExtension];
    NSString *assetFilename = [NSString stringWithFormat:@"asset_%@.%@",libraryId,assetFileExt];
    return [NSString stringWithFormat:@"%@/%@", assetFolder, assetFilename];
}

+ (NSURL *) cachedAudioURLForMPMediaItem:(MPMediaItem*) item {
    NSString *assetFilepath = [[self class] cachedAudioFilepathForMPMediaItem:item];
    return [NSURL fileURLWithPath:assetFilepath];
}

Ahora el método init que hace "el negocio"

- (id) initWithMPMediaItem:(MPMediaItem*) item 
           completionBlock:(void (^)(UIImage* delayedImagePreparation))completionBlock  {

    NSFileManager *fman = [NSFileManager defaultManager];
    NSString *assetPictogramFilepath = [[self class] cachedAudioPictogramPathForMPMediaItem:item];

    if ([fman fileExistsAtPath:assetPictogramFilepath]) {

        NSLog(@"Returning cached waveform pictogram: %@",[assetPictogramFilepath lastPathComponent]);

        self = [self initWithContentsOfFile:assetPictogramFilepath];
        return self;
    }

    NSString *assetFilepath = [[self class] cachedAudioFilepathForMPMediaItem:item];

    NSURL *assetFileURL = [NSURL fileURLWithPath:assetFilepath];

    if ([fman fileExistsAtPath:assetFilepath]) {

        NSLog(@"scanning cached audio data to create UIImage file: %@",[assetFilepath lastPathComponent]);

        [assetFileURL retain];
        [assetPictogramFilepath retain];

        [NSThread MCSM_performBlockInBackground: ^{

            AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:assetFileURL options:nil];
            NSData *waveFormData = [self renderPNGAudioPictogramForAsset:asset]; 

            [waveFormData writeToFile:assetPictogramFilepath atomically:YES];

            [assetFileURL release];
            [assetPictogramFilepath release];

            if (completionBlock) {

                [waveFormData retain];
                [NSThread MCSM_performBlockOnMainThread:^{

                    UIImage *result = [UIImage imageWithData:waveFormData];

                    NSLog(@"returning rendered pictogram on main thread (%d bytes %@ data in UIImage %0.0f x %0.0f pixels)",waveFormData.length,[imgExt uppercaseString],result.size.width,result.size.height);

                    completionBlock(result);

                    [waveFormData release];
                }];
            }
        }];

        return nil;

    } else {

        NSString *assetFolder = [[self class] assetCacheFolder];

        [fman createDirectoryAtPath:assetFolder withIntermediateDirectories:YES attributes:nil error:nil];

        NSLog(@"Preparing to import audio asset data %@",[assetFilepath lastPathComponent]);

        [assetPictogramFilepath retain];
        [assetFileURL retain];

        TSLibraryImport* import = [[TSLibraryImport alloc] init];
        NSURL    * assetURL = [item valueForProperty:MPMediaItemPropertyAssetURL];

         [import importAsset:assetURL toURL:assetFileURL completionBlock:^(TSLibraryImport* import) {
            //check the status and error properties of
            //TSLibraryImport

            if (import.error) {

                NSLog (@"audio data import failed:%@",import.error);

            } else{
                NSLog (@"Creating waveform pictogram file: %@", [assetPictogramFilepath lastPathComponent]);
                AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:assetFileURL options:nil];
                NSData *waveFormData = [self renderPNGAudioPictogramForAsset:asset]; 

                [waveFormData writeToFile:assetPictogramFilepath atomically:YES];

                if (completionBlock) {
                     [waveFormData retain];
                    [NSThread MCSM_performBlockOnMainThread:^{

                        UIImage *result = [UIImage imageWithData:waveFormData];
                        NSLog(@"returning rendered pictogram on main thread (%d bytes %@ data in UIImage %0.0f x %0.0f pixels)",waveFormData.length,[imgExt uppercaseString],result.size.width,result.size.height);

                        completionBlock(result);

                        [waveFormData release];
                    }];
                }
            }

            [assetPictogramFilepath release];
            [assetFileURL release];

        }  ];

        return nil;
    }
}

Un ejemplo de invocación de esto:

-(void) importMediaItem {

    MPMediaItem* item = [self mediaItem];

    // since we will be needing this for playback, save the url to the cached audio.
    [url release];
    url = [[UIImage cachedAudioURLForMPMediaItem:item] retain];

    [waveFormImage release];

    waveFormImage = [[UIImage alloc ] initWithMPMediaItem:item completionBlock:^(UIImage* delayedImagePreparation){

        waveFormImage = [delayedImagePreparation retain];
        [self displayWaveFormImage];
    }];

    if (waveFormImage) {
        [waveFormImage retain];
        [self displayWaveFormImage];
    }
}

Versión logarítmica de los métodos de promediado y renderizado

#define absX(x) (x<0?0-x:x)
#define minMaxX(x,mn,mx) (x<=mn?mn:(x>=mx?mx:x))
#define noiseFloor (-90.0)
#define decibel(amplitude) (20.0 * log10(absX(amplitude)/32767.0))

-(UIImage *) audioImageLogGraph:(Float32 *) samples
                normalizeMax:(Float32) normalizeMax
                 sampleCount:(NSInteger) sampleCount 
                channelCount:(NSInteger) channelCount
                 imageHeight:(float) imageHeight {

    CGSize imageSize = CGSizeMake(sampleCount, imageHeight);
    UIGraphicsBeginImageContext(imageSize);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [UIColor blackColor].CGColor);
    CGContextSetAlpha(context,1.0);
    CGRect rect;
    rect.size = imageSize;
    rect.origin.x = 0;
    rect.origin.y = 0;

    CGColorRef leftcolor = [[UIColor whiteColor] CGColor];
    CGColorRef rightcolor = [[UIColor redColor] CGColor];

    CGContextFillRect(context, rect);

    CGContextSetLineWidth(context, 1.0);

    float halfGraphHeight = (imageHeight / 2) / (float) channelCount ;
    float centerLeft = halfGraphHeight;
    float centerRight = (halfGraphHeight*3) ; 
    float sampleAdjustmentFactor = (imageHeight/ (float) channelCount) / (normalizeMax - noiseFloor) / 2;

    for (NSInteger intSample = 0 ; intSample < sampleCount ; intSample ++ ) {
        Float32 left = *samples++;
        float pixels = (left - noiseFloor) * sampleAdjustmentFactor;
        CGContextMoveToPoint(context, intSample, centerLeft-pixels);
        CGContextAddLineToPoint(context, intSample, centerLeft+pixels);
        CGContextSetStrokeColorWithColor(context, leftcolor);
        CGContextStrokePath(context);

        if (channelCount==2) {
            Float32 right = *samples++;
            float pixels = (right - noiseFloor) * sampleAdjustmentFactor;
            CGContextMoveToPoint(context, intSample, centerRight - pixels);
            CGContextAddLineToPoint(context, intSample, centerRight + pixels);
            CGContextSetStrokeColorWithColor(context, rightcolor);
            CGContextStrokePath(context); 
        }
    }

    // Create new image
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    // Tidy up
    UIGraphicsEndImageContext();   

    return newImage;
}

- (NSData *) renderPNGAudioPictogramLogForAsset:(AVURLAsset *)songAsset {

    NSError * error = nil;
    AVAssetReader * reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];
    AVAssetTrack * songTrack = [songAsset.tracks objectAtIndex:0];

    NSDictionary* outputSettingsDict = [[NSDictionary alloc] initWithObjectsAndKeys:
                                        [NSNumber numberWithInt:kAudioFormatLinearPCM],AVFormatIDKey,
                                        //     [NSNumber numberWithInt:44100.0],AVSampleRateKey, /*Not Supported*/
                                        //     [NSNumber numberWithInt: 2],AVNumberOfChannelsKey,    /*Not Supported*/

                                        [NSNumber numberWithInt:16],AVLinearPCMBitDepthKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsBigEndianKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
                                        [NSNumber numberWithBool:NO],AVLinearPCMIsNonInterleaved,
                                        nil];

    AVAssetReaderTrackOutput* output = [[AVAssetReaderTrackOutput alloc] initWithTrack:songTrack outputSettings:outputSettingsDict];

    [reader addOutput:output];
    [output release];

    UInt32 sampleRate,channelCount;

    NSArray* formatDesc = songTrack.formatDescriptions;
    for(unsigned int i = 0; i < [formatDesc count]; ++i) {
        CMAudioFormatDescriptionRef item = (CMAudioFormatDescriptionRef)[formatDesc objectAtIndex:i];
        const AudioStreamBasicDescription* fmtDesc = CMAudioFormatDescriptionGetStreamBasicDescription (item);
        if(fmtDesc ) {

            sampleRate = fmtDesc->mSampleRate;
            channelCount = fmtDesc->mChannelsPerFrame;

            //    NSLog(@"channels:%u, bytes/packet: %u, sampleRate %f",fmtDesc->mChannelsPerFrame, fmtDesc->mBytesPerPacket,fmtDesc->mSampleRate);
        }
    }

    UInt32 bytesPerSample = 2 * channelCount;
    Float32 normalizeMax = noiseFloor;
    NSLog(@"normalizeMax = %f",normalizeMax);
    NSMutableData * fullSongData = [[NSMutableData alloc] init];
    [reader startReading];

    UInt64 totalBytes = 0; 
    Float64 totalLeft = 0;
    Float64 totalRight = 0;
    Float32 sampleTally = 0;

    NSInteger samplesPerPixel = sampleRate / 50;

    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);
            totalBytes += length;

            NSAutoreleasePool *wader = [[NSAutoreleasePool alloc] init];

            NSMutableData * data = [NSMutableData dataWithLength:length];
            CMBlockBufferCopyDataBytes(blockBufferRef, 0, length, data.mutableBytes);

            SInt16 * samples = (SInt16 *) data.mutableBytes;
            int sampleCount = length / bytesPerSample;
            for (int i = 0; i < sampleCount ; i ++) {

                Float32 left = (Float32) *samples++;
                left = decibel(left);
                left = minMaxX(left,noiseFloor,0);
                totalLeft  += left;

                Float32 right;
                if (channelCount==2) {
                    right = (Float32) *samples++;
                    right = decibel(right);
                    right = minMaxX(right,noiseFloor,0);
                    totalRight += right;
                }

                sampleTally++;

                if (sampleTally > samplesPerPixel) {

                    left  = totalLeft / sampleTally; 
                    if (left > normalizeMax) {
                        normalizeMax = left;
                    }

                   // NSLog(@"left average = %f, normalizeMax = %f",left,normalizeMax);

                    [fullSongData appendBytes:&left length:sizeof(left)];

                    if (channelCount==2) {
                        right = totalRight / sampleTally; 

                        if (right > normalizeMax) {
                            normalizeMax = right;
                        }

                        [fullSongData appendBytes:&right length:sizeof(right)];
                    }

                    totalLeft   = 0;
                    totalRight  = 0;
                    sampleTally = 0;
                }
            }

           [wader drain];

            CMSampleBufferInvalidate(sampleBufferRef);
            CFRelease(sampleBufferRef);
        }
    }

    NSData * finalData = nil;

    if (reader.status == AVAssetReaderStatusFailed || reader.status == AVAssetReaderStatusUnknown){
        // Something went wrong. Handle it.
    }

    if (reader.status == AVAssetReaderStatusCompleted){
        // You''re done. It worked.

        NSLog(@"rendering output graphics using normalizeMax %f",normalizeMax);

        UIImage *test = [self audioImageLogGraph:(Float32 *) fullSongData.bytes 
                                 normalizeMax:normalizeMax 
                                  sampleCount:fullSongData.length / (sizeof(Float32) * 2) 
                                 channelCount:2
                                  imageHeight:100];

        finalData = imageToData(test);
    }

    [fullSongData release];
    [reader release];

    return finalData;
}

salidas de comparación

Diagrama lineal para el inicio de "Warm It Up" de Acme Swing Company

Trama logarítmica para el inicio de "Warm It Up" de Acme Swing Company