在3GS设备上，无法使用AVAssetWriter从图像创建影片

CVPixelBufferRef buffer = NULL;
buffer = [self pixelBufferFromCGImage:[[UIImage imageNamed:@\"frame1.png\"] CGImage]];
BOOL result = [adaptor appendPixelBuffer:buffer withPresentationTime:kCMTimeZero];

if (result == NO) //failes on 3GS, but works on iphone 4
    NSLog(@\"failed to append buffer\");

-(void)writeImagesAsMovie:(NSArray *)array toPath:(NSString*)path {


NSLog(path);

NSError *error = nil;
AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:
                              [NSURL fileURLWithPath:path] fileType:AVFileTypeQuickTimeMovie
                                                          error:&error];

if(error) {
    NSLog(@\"error creating AssetWriter: %@\",[error description]);
}

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt:frameSize.width], AVVideoWidthKey,
                               [NSNumber numberWithInt:frameSize.height], AVVideoHeightKey,
                               nil];



AVAssetWriterInput* writerInput = [[AVAssetWriterInput
                                    assetWriterInputWithMediaType:AVMediaTypeVideo
                                    outputSettings:videoSettings] retain];

NSMutableDictionary *attributes = [[NSMutableDictionary alloc]init];
[attributes setObject:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32ARGB] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];
[attributes setObject:[NSNumber numberWithUnsignedInt:frameSize.width] forKey:(NSString*)kCVPixelBufferWidthKey];
[attributes setObject:[NSNumber numberWithUnsignedInt:frameSize.height] forKey:(NSString*)kCVPixelBufferHeightKey];

AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor
                                                 assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
                                                 sourcePixelBufferAttributes:attributes];

[videoWriter addInput:writerInput];

// fixes all errors
writerInput.expectsMediaDataInRealTime = YES;

//Start a session:
BOOL start = [videoWriter startWriting];
NSLog(@\"Session started? %d\", start);

[videoWriter startSessionAtSourceTime:kCMTimeZero];

CVPixelBufferRef buffer = NULL;
buffer = [self pixelBufferFromCGImage:[[UIImage imageNamed:@\"frame1.png\"] CGImage]];
BOOL result = [adaptor appendPixelBuffer:buffer withPresentationTime:kCMTimeZero];

if (result == NO) //failes on 3GS, but works on iphone 4
    NSLog(@\"failed to append buffer\");

if(buffer)
    CVBufferRelease(buffer);

[NSThread sleepForTimeInterval:0.05];
//for (int i = 1;i<[array count]; i++)
for (int i = 1;i<20; i++)
{
    if (adaptor.assetWriterInput.readyForMoreMediaData) 
    {
        NSLog(@\"inside for loop %d\",i);
        CMTime frameTime = CMTimeMake(1, 15);
        CMTime lastTime=CMTimeMake(i, 15); 
        CMTime presentTime=CMTimeAdd(lastTime, frameTime);
        NSString *imgName = [NSString stringWithFormat:@\"frame%d.png\",i];
        UIImage *imgFrame = [UIImage imageNamed:imgName] ;
        buffer = [self pixelBufferFromCGImage:[imgFrame CGImage]];
        BOOL result = [adaptor appendPixelBuffer:buffer withPresentationTime:presentTime];

        if (result == NO) //failes on 3GS, but works on iphone 4
        {
            NSLog(@\"failed to append buffer\");
            NSLog(@\"The error is %@\", [videoWriter error]);
        }
        if(buffer)
            CVBufferRelease(buffer);
        [NSThread sleepForTimeInterval:0.05];
    }
    else
    {
        NSLog(@\"error\");
        i--;
    }
}

//Finish the session:
[writerInput markAsFinished];
[videoWriter finishWriting];
CVPixelBufferPoolRelease(adaptor.pixelBufferPool);
[videoWriter release];
[writerInput release];

NSLog(@\"Movie created successfully\");

}

- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image
{
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                             nil];
    CVPixelBufferRef pxbuffer = NULL;

    CVPixelBufferCreate(kCFAllocatorDefault, self.view.frame.size.width,
                        self.view.frame.size.height, kCVPixelFormatType_32ARGB, (CFDictionaryRef) options, 
                        &pxbuffer);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, self.view.frame.size.width,
                                                 self.view.frame.size.height, 8, 4*self.view.frame.size.width, rgbColorSpace, 
                                                 kCGImageAlphaNoneSkipFirst);

    CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), 
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}