CVPixelBufferCreateWithIOSurface: Get pixels from IOSurfaceRef

Question

I'm trying to create a CVPixelBufferRef from an IOSurfaceRef in order to be able to read its pixels values.

The IOSurfaceRef is read from the Syphon (website and repo) framework's SyphonOpenGLClient. My code is inspired from the Simple Client example that can be found here and is based on the Apple's documentation about CVPixelBufferCreateWithIOSurface.

Here it is:

m_client = [[SyphonOpenGLClient alloc] initWithServerDescription:[serverDescription copy]
                                                              context:CGLGetCurrentContext()
                                                              options:nil 
                                                      newFrameHandler:^(SyphonOpenGLClient *client) {

      // Get the new frame produced by the client.
      SyphonImageBase *frame = (SyphonImageBase *)[client newFrameImage];

      // It works: IOSurfaceRef exists.
      m_width = IOSurfaceGetWidth((IOSurfaceRef)[frame surface]);
      m_height = IOSurfaceGetHeight((IOSurfaceRef)[frame surface]);

      CVPixelBufferRef buffer = NULL;
      CVPixelBufferCreateWithIOSurface(kCFAllocatorDefault, (IOSurfaceRef)[frame surface], NULL, &buffer);

      // Logs 0x0
      NSLog(@"Buffer: %p", buffer);

    }];

I'm really not a specialist of CoreVideo, I'm tinkering a lot.

I would like to understand how to get pixels from an IOSurfaceRef.

Thank you.