iphone - 使用 AVAssetReader 绘制波形

Question

我使用assetUrl 从iPod 库中读取歌曲(代码名为audioUrl)我可以以多种方式播放它，我可以剪切它，我可以用它进行一些进动，但是......我真的不明白我要用这个 CMSampleBufferRef 做什么来获取绘制波形的数据!我需要有关峰值的信息，我如何才能以这种方式(也许是另一种方式)获得它？

    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? */}

请帮帮我!

Answer 1

我正在寻找类似的东西，并决定“自己动手”。我意识到这是一个旧帖子，但如果其他人正在寻找这个，这是我的解决方案。它相对快速和肮脏，并将图像标准化为“全尺寸”。它创建的图像是“宽的”，即您需要将它们放在 UIScrollView 中或以其他方式管理显示。

这是基于对 this question 的一些回答。

样本输出

编辑:我添加了平均和渲染方法的对数版本，请参阅此消息的末尾以了解替代版本和比较输出。我个人更喜欢原始的线性版本，但已决定发布它，以防有人可以改进所使用的算法。

您将需要这些导入:

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

首先，一个通用的渲染方法，它接受一个指向平均样本数据的指针，
并返回一个 UIImage。请注意，这些样本不是可播放的音频样本。

-(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;
}

接下来，一个接受 AVURLAsset 并返回 PNG 图像数据的方法

- (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;
}

高级选项:最后，如果您希望能够使用 AVAudioPlayer 播放音频，则需要缓存它到您的应用程序的捆绑缓存文件夹。既然我这样做了，我决定缓存图像数据此外，并将整个事物包装到 UIImage 类别中。你需要包括this open source offering从 here 中提取音频和一些代码处理一些后台线程功能。

首先，一些定义，以及一些用于处理路径名等的通用类方法

//#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];
}

现在是做“生意”的init方法

- (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;
    }
}

调用这个的一个例子:

-(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];
    }
}

平均和渲染方法的对数版本

#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;
}

比较输出

Acme Swing Company 的“Warm It Up”开始的线性图

Acme Swing Company 的“Warm It Up”开始的对数图