MPEG Video Technology

Virtual Lab Tour: Vision Systems for Mobile Robots

By: Soradech KrootjohnVanderbilt University

Center for Intelligent Systems

Feb. 15, 2006

What is MPEG?

• MPEG (Moving Picture Experts Group)

• Used for coding audio-visual information in a digital compressed format

• MP3 is the audio-only portion of MPEG and is commonly used for music.

Where can we find MPEG video?

• MPEG-1– Video CD, Video clips on Internet

• MPEG-2– DVD– Digital Cable TV & Satellite TV

• MPEG-4– Supports a wide range of applications:

• Wireless/mobile multimedia such as videos on cell-phone or video clips on internet (higher quality than MPEG-1)

• Video production in studios

Digital Video Signal

• Digital video signal is composed of a series of still images, representing a natural visual scene.

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Video Clip Sample

Frame:

How MPEG Works?

• Encode only changes occurring between video frames by predicting motion occuring between frames

• Each video frame may be encoded as:• I Frame:

– Simply encode current frame as it appears (No prediction)

• P Frame:– Current frame is predicted based on the previous frame

• B Frame:– Current frame is predicted based on the previous and future

frames

P-Frame Prediction

Current P FramePrevious I or P Frame

B-Frame Prediction

• Bi-Directional Predicted Frame

Current B Frame

Previous I or P Frame Future I or P Frame

Both Previous and Future I or P Frames

Macroblocks

Divide current frame into Macroblocks (16x16 pixels)

Previous Frame(Reference Frame)

Current Frame(Predicted Frame)

Motion Vectors

• Current frame is divided into Macroblocks

• The Motion Vector describes the direction and distance the current Macroblock moved from the previous frame to the current frame

• We use these Motion Vectors to enable the robot to detect motion.