Should use GPUImage - https://github.com/BradLarson/GPUImage - for this. Runs on GPU so it is fast enough I think. You'll need convert UIImages
from CMSampleBuffers
that AVCaptureSession
spits out. This - https://github.com/eppz/eppz.capture/blob/master/eppz!capture/EPPZCaptureBufferParser.m#L81 - may help.
// Create filter.
self.blurFilter = [GPUImageiOSBlurFilter new];
// Apply filter.
UIImage *blurredSnapshotImage = [self.blurFilter imageByFilteringImage:snapshotImage];