FPX Video Recoder Module

Introduction

The FPX Video Recoder can limit the bandwidth of video traffic sent over the network during times of network congestion without reducing the video frame rate.  A Video Recoder module has been implemented for the Field-programmable Port Extender (FPX) to recode variable-length integers from Motion-JPEG data stream. The Video Recoder recompresses JPEG images midway through the network by discarding the high frequency coefficients.  The result is a Motion-JPEG video bitstream with up-to-N coefficients and smaller bandwidth requirements. 

Configuration

An Motion-JPEG video source (MMX) streams sequential JPEG images in AAL0 cell format at a rate of up to 15 Mbits/sec ¹.  The FPX Video Recoder can recompress each JPEG image over a range from 0.93 bits-per-pixel down to 0.51 bits-per-pixel (color) or 0.38 bits-per-pixel (grayscale) by passing up-to-N coefficients of 8x8 blocks.  During the recoding process entropy values are decoded bit-serial, blocks are quantized by dropping image coefficients, and the remaining entropy values are recoded as JPEG data.  The Video Recoder is also useful in that it demonstrates the FPX hardware's capability to be used for real-time video processing applications such as developing a full JPEG image decoder and encoder.

In the Bryan 420 laboratory, an MMX video station is connected with OC3 fiber to a WUGS switch that contains several FPX cards.  The Video Recoder module is programmed into a single FPX using the NCHARGE control software.  Virtual circuit paths are added to route JPEG data from the MMX to the one of the FPX modules on VCI 101 and control cells on VCI 35.  A camera and monitor are connected to the MMX station using standard RCA video cables. 

Design

• Video Recoder module data path

Recoded Images

The images below were passed through the JPEG Video Recoder circuit.  The are cropped from their original 640x248 resolution.  They are represented in a luminance/chrominance form (YCbCr), where the caption describes the amount of luminance (Y), chrominance blue (Cb), and chrominance red (Cr) per coded data unit.

(Normal video) 17.14 KB, 0.88 bits-per-pixel	up to 8 Y, 8 Cb, 8 Cr 11.78 KB, 0.61 bits-per-pixel
up to 4 Y, 4 Cb, 4 Cr 9.29 KB, 0.48 bits-per-pixel	up to 2 Y, 2 Cb, 2 Cr 5.60 KB, 0.289 bits-per-pixel
up to 1 Y, 1 Cb, 1 Cr 4.35 KB, 0.22 bits-per-pixel

Presentations

• JPEG Video Recoder Slideshow in Adobe Acrobat format

¹ MMX Q-factor set to 25 to create the quantization tables

FPX Homepage
Last updated 06/13/2002 by cen1@arl.wustl.edu