VideoTag

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VideoTag

• Video Display and Recording
• Aaron Shepler

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Motivation

• Enable the user to view real-time video from the
  camera
• Allow the user to annotate on top of the video
  image
• Facilitate simple video recording

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Previous / Related Work

• Point Grey Research has written a C wrapper for
  reading/writing to an AVI
• Microsoft is working on an InkCanvas control (to
  be released in Vista) that would potentially
  allow for something similar inking on multimedia

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Challenges

• How do I use the camera in C when the interface
  is in C?
• The .NET framework allows for easy integration
  between different managed types of code i.e.
  Managed C and Managed C
• Integration between unmanaged code and managed
  code is not very well documented

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Challenges

• How do I place the image on the screen once I
  have data using C?
• Lower level operations, such as direct access to
  screen are not available

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Challenges

• How do I manage the recording of the video
• C does not have built-in AVI recording
  functionality
• Function calls from C would also have to be
  wrapped

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Camera Approach / Solution

• Two possible approaches that allow for use of
  camera in C
• Link in flycapture camera methods directly
• Large blocks of unsafe code due to use of
  pointers
• Link in a library that simplifies the interface
• Few lines of unsafe code

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Camera Approach / Solution

• Mistake
• First tried to link in flycapture camera methods
  directly
• Unsafe blocks of code were everywhere due to
  the use of pointers
• Became a C-based program
• Learned my lesson the hard way

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Camera Approach / Solution

• Encapsulated lower level camera functionality in
  a library
• Created a small library of methods
• Interface was well defined
• Less time spent matching compatible types

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Camera Approach / Solution

• CameraLib
• Library with basic camera functionality
• void initialize()
• Initializes the first camera on the FireWire bus,
  creates context, etc
• void grabImage(unsigned char)
• Retrieves an image based on the camera context
• void destroy()
• Destroys the camera context
• Pure C library for use in managed code

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Video Approach / Solution

• In order to place the image onto the screen, the
  InkPicture control was used
• Allows the background image to be changed while
  maintaining the ink on top.
• Create thread in C
• continuous capturing / refreshing the image

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Recording Approach

• Record to Avi using C wrapper class
• Same refresh thread adds the current bitmap to
  the next frame in the AVI
• Pro
• Easy to access bitmaps out of the AVI later
• Con
• Large file is unhandy
• Avi wrapper written orginally by René Nyffenegger
  (modified by John Corinna), located at
• http//www.codeproject.com/csharp/steganodotnet4.a
  sp

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Demonstration
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Discussion

• How can we reduce the slight flicker with the
  video/ink?
• Double buffering?
• User Drawn Control?

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Discussion

• What methods of encoding the video data would be
  faster and more robust than AVI?
• Various compression models?
• Existing codecs?