IPhone: Video API: Live video streaming modify

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I have a question about video stream processing. Is it possible to get access and modify real time video stream during recording (f.e. I want to add some text to video)? I can do this as a preview by getting separate frames, but I'm looking for tool which will allow me to store video with my text in video frames.

Probably there is already some libraries/tools available (but I haven't found any yet).