Retaining CMSampleBufferRef cause random crashes

Question

I'm using captureOutput:didOutputSampleBuffer:fromConnection: in order to keep track of the frames. For my use-case, I only need to store the last frame and use it in case the app goes to background.

That's a sample from my code:

@property (nonatomic, strong) AVCaptureVideoDataOutput *videoDataOutput;
@property (atomic) CMSampleBufferRef currentBuffer;

- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
{
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef con = CGBitmapContextCreate(baseAddress, width, height, 8,
                                             bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(con);
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(con);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    //    UIImage *image = [UIImage imageWithCGImage:quartzImage];
    UIImage *image =  [UIImage imageWithCGImage:quartzImage scale:[[UIScreen mainScreen] scale] orientation:UIImageOrientationRight];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}
//[self.videoDataOutput setSampleBufferDelegate:self queue:self.sessionQueue];

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    CFRetain(sampleBuffer);

    @synchronized (self) {
        if (_currentBuffer) {
            CFRelease(_currentBuffer);
        }
        self.currentBuffer = sampleBuffer;
    }
}

- (void) goingToBackground:(NSNotification *) notification
{
    UIImage *snapshot = [self imageFromSampleBuffer:_currentBuffer];

    //Doing something with snapshot...
}

The problem is that in some cases I get this crash from within imageFromSampleBuffer:

<Error>: copy_read_only: vm_copy failed: status 1.

The crash happens on CGImageRef quartzImage = CGBitmapContextCreateImage(con);

What am I doing wrong?

Could you show your code for the method imageFromSampleBuffer: — SheffieldKevin, Oct 11 '15 at 11:09
Added answer how to take sampleBuffer ownership here: http://stackoverflow.com/a/36893192/440168 — k06a, Apr 27 '16 at 14:44
Possible duplicate of [AVCaptureSession returning blank image on iPhone 3G only](https://stackoverflow.com/questions/3954952/avcapturesession-returning-blank-image-on-iphone-3g-only) — kenorb, May 29 '17 at 16:24

score 0 · Answer 1 · answered Aug 25 '22 at 02:00

I believe you need to copy the buffer, not just retain. From the description for captureOutput:didOutputSampleBuffer:fromConnection:

Note that to maintain optimal performance, some sample buffers directly reference pools of memory that may need to be reused by the device system and other capture inputs. [...] If multiple sample buffers reference such pools of memory for too long, inputs will no longer be able to copy new samples into memory and those samples will be dropped.

Retaining CMSampleBufferRef cause random crashes

1 Answers1