EXC_Bad_Access while analyzing sampleBuffer in OpenCV - c++

Question

I am trying to to do a real-time camera processing with OpenCV.
In the didOutputSampleBuffer-Method of AVCaptureVideoDataOutputSampleBufferDelegate I am creating a matrix out of a sampleBuffer (which works without any problems). But when performing certain methods, such as cv::GaussianBlur, the app crashes because of "exc_bad_access code=1, address = 0x10......". Do you know why?
cv::Mat matrix(bufferHeight, bufferWidth, CV_8UC4, baseAddress);
cv::GaussianBlur(matrix, matrix, cvSize(5,5), 0); // Crahes here
__ Edit:
Base Address is calculated as below (this is done in Swift in didOutputSampleBuffer-Method, before passing these variables to objective-c++)
var pixelBuffer: CVImageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
var baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)
____ Edit2:
Value of baseAddress:
0x0000000107790000
Value of pixelBuffer:
<CVPixelBuffer 0x17413aae0 width=1920 height=1080 pixelFormat=420v iosurface=0x1700039e0 planes=2>
<Plane 0 width=1920 height=1080 bytesPerRow=1920>
<Plane 1 width=960 height=540 bytesPerRow=1920>
<attributes=<CFBasicHash 0x17426e640 [0x1b8d18bb8]>{type = immutable dict, count = 5,
entries =>
0 : <CFString 0x1b300de28 [0x1b8d18bb8]>{contents = "PixelFormatDescription"} = <CFBasicHash 0x17426a080 [0x1b8d18bb8]>{type = immutable dict, count = 10,
entries =>
0 : <CFString 0x1b300e088 [0x1b8d18bb8]>{contents = "Planes"} = (
{
BitsPerBlock = 8;
BlackBlock = <10>;
FillExtendedPixelsCallback = <00000000 00000000 b840aa95 01000000 00000000 00000000>;
},
{
BitsPerBlock = 16;
BlackBlock = <8080>;
FillExtendedPixelsCallback = <00000000 00000000 443faa95 01000000 00000000 00000000>;
HorizontalSubsampling = 2;
VerticalSubsampling = 2;
}
)
2 : <CFString 0x1b300dd68 [0x1b8d18bb8]>{contents = "IOSurfaceOpenGLESFBOCompatibility"} = <CFBoolean 0x1b8d19110 [0x1b8d18bb8]>{value = true}
3 : <CFString 0x1b300e228 [0x1b8d18bb8]>{contents = "ContainsYCbCr"} = <CFBoolean 0x1b8d19110 [0x1b8d18bb8]>{value = true}
4 : <CFString 0x1b300dd48 [0x1b8d18bb8]>{contents = "IOSurfaceOpenGLESTextureCompatibility"} = <CFBoolean 0x1b8d19110 [0x1b8d18bb8]>{value = true}
5 : <CFString 0x1b300e288 [0x1b8d18bb8]>{contents = "ComponentRange"} = <CFString 0x1b300e2a8 [0x1b8d18bb8]>{contents = "VideoRange"}
6 : <CFString 0x1b300e008 [0x1b8d18bb8]>{contents = "PixelFormat"} = <CFNumber 0xb000000343230762 [0x1b8d18bb8]>{value = [phone], type = kCFNumberSInt32Type}
7 : <CFString 0x1b300dd28 [0x1b8d18bb8]>{contents = "IOSurfaceCoreAnimationCompatibility"} = <CFBoolean 0x1b8d19110 [0x1b8d18bb8]>{value = true}
9 : <CFString 0x1b300e068 [0x1b8d18bb8]>{contents = "ContainsAlpha"} = <CFBoolean 0x1b8d19120 [0x1b8d18bb8]>{value = false}
10 : <CFString 0x1b300e248 [0x1b8d18bb8]>{contents = "ContainsRGB"} = <CFBoolean 0x1b8d19120 [0x1b8d18bb8]>{value = false}
11 : <CFString 0x1b300dd88 [0x1b8d18bb8]>{contents = "OpenGLESCompatibility"} = <CFBoolean 0x1b8d19110 [0x1b8d18bb8]>{value = true}
}
2 : <CFString 0x1b300dbe8 [0x1b8d18bb8]>{contents = "ExtendedPixelsRight"} = <CFNumber 0xb000000000000002 [0x1b8d18bb8]>{value = +0, type = kCFNumberSInt32Type}
3 : <CFString 0x1b300dbc8 [0x1b8d18bb8]>{contents = "ExtendedPixelsTop"} = <CFNumber 0xb000000000000002 [0x1b8d18bb8]>{value = +0, type = kCFNumberSInt32Type}
4 : <CFString 0x1b300dba8 [0x1b8d18bb8]>{contents = "ExtendedPixelsLeft"} = <CFNumber 0xb000000000000002 [0x1b8d18bb8]>{value = +0, type = kCFNumberSInt32Type}
5 : <CFString 0x1b300dc08 [0x1b8d18bb8]>{contents = "ExtendedPixelsBottom"} = <CFNumber 0xb000000000000082 [0x1b8d18bb8]>{value = +8, type = kCFNumberSInt32Type}
}
propagatedAttachments=<CFBasicHash 0x17426e900 [0x1b8d18bb8]>{type = mutable dict, count = 4,
entries =>
0 : <CFString 0x1b300d7c8 [0x1b8d18bb8]>{contents = "CVImageBufferYCbCrMatrix"} = <CFString 0x1b300d7e8 [0x1b8d18bb8]>{contents = "ITU_R_709_2"}
1 : <CFString 0x1b300d928 [0x1b8d18bb8]>{contents = "CVImageBufferTransferFunction"} = <CFString 0x1b300d7e8 [0x1b8d18bb8]>{contents = "ITU_R_709_2"}
2 : <CFString 0x1b3044fa0 [0x1b8d18bb8]>{contents = "MetadataDictionary"} = <CFBasicHash 0x170077840 [0x1b8d18bb8]>{type = mutable dict, count = 3,
entries =>
0 : <CFString 0x1b304d100 [0x1b8d18bb8]>{contents = "SNR"} = <CFNumber 0x170036300 [0x1b8d18bb8]>{value = +28.30700356903138370512, type = kCFNumberFloat64Type}
1 : <CFString 0x1b304b2e0 [0x1b8d18bb8]>{contents = "ExposureTime"} = <CFNumber 0x170033d00 [0x1b8d18bb8]>{value = +0.01000000000000000021, type = kCFNumberFloat64Type}
2 : <CFString 0x1b304d0e0 [0x1b8d18bb8]>{contents = "SensorID"} = <CFNumber 0xb000000000002472 [0x1b8d18bb8]>{value = +583, type = kCFNumberSInt32Type}
}
5 : <CFString 0x1b300d8a8 [0x1b8d18bb8]>{contents = "CVImageBufferColorPrimaries"} = <CFString 0x1b300d7e8 [0x1b8d18bb8]>{contents = "ITU_R_709_2"}
}
nonPropagatedAttachments=<CFBasicHash 0x17426e8c0 [0x1b8d18bb8]>{type = mutable dict, count = 0,
entries =>
}

Answer 1

Ah - your video data is not 4 component RGBA (or whatever), but "1.5" component YUV. You should either perform the blur in YUV, or perhaps more easily, switch your capture session to RGBA.
YUV is the default format & you've got two "planes" in it.
Plane 0 is "Y", a 1920x1080 8-bit bitmap, and plane 1 is "UV", a 960x540 16-bit bitmap (actually two 960x540 8-bit bitmaps side by side, U & V, not sure why they're not split into 3 planes really).
In any case, your code is expecting a 1920x1080 32-bit bitmap, and runs off the end of the Y channel's memory.
If you want to switch to RGBA, do (I think - I can never remember which 4 component format iOS uses):
output.videoSettings = [kCVPixelBufferPixelFormatTypeKey as AnyHashable: kCVPixelFormatType_32BGRA]
If you're feeling adventurous, do the blur on the yuv data - it's 2.666666667 times smaller, and your code could be 2.666667 times faster.