[Pyobjc-dev] How to get (void*) data into a Python array

[Trevor B. <mr...@gm...>]

Hello,

I am working on a small Python script to grab a single frame from the
iSight camera using PyObjC.  I want to import the frame into a python
numpy array for manipulation, and I want to write it exclusively in
Python.  I have fairly limited experience in Python and Objective-C, and
no prior experience with PyObjC.

I have made some progress, and currently it is able to find the camera,
open it, and capture a frame.  The frame data is (theoretically)
available in my QTCaptureDecompressedVideoOutput delegate's callback
function:

- (void)captureOutput:(QTCaptureOutput *)captureOutput
didOutputVideoFrame:(CVImageBufferRef)videoFrame
withSampleBuffer:(QTSampleBuffer *)sampleBuffer
fromConnection:(QTCaptureConnection *)connection

So I added "pdb.set_trace()" at the beginning of the callback, and am
trying to figure out how to get the raw bytes available in Python.

The closest I have come is examining sampleBuffer:
--------------------------------------------------
(Pdb) sampleBuffer
<QTSampleBuffer: 0x1044b42d0>
(Pdb) sampleBuffer.numberOfSamples()
1
(Pdb) sampleBuffer.lengthForAllSamples()
2624000
(Pdb) sampleBuffer.bytesForAllSamples()
4674363392L
--------------------------------------------------

However, this is where I'm confused.  bytesForAllSamples() returns a
(void*), which is literally, of course, a long integer.  I have no idea
how to get at those bytes, since I'm assuming I can't just dereference
an ObjC pointer somehow in Python.  I was hoping an NSData object
initialized with the address would work, but it does not:

--------------------------------------------------
(Pdb)
NSData.dataWithBytes_length_(sampleBuffer.bytesForAllSamples(),2624000)
*** TypeError: converting to a C array
--------------------------------------------------

Any guidance in getting past this point would be much appreciated!  And
thanks to everyone responsible for PyObjC, it is an excellent resource.

-Trevor