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Disclaimer: This document was part of the First European DSP Education and Research Conference. It may have been written by someone whose native language is not English. TI assumes no liability for the quality of writing and/or the accuracy of the information contained herein.
Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP
Authors: F. Bonomini, F. De Marco-Zompit, G.A. Mian, A. Odorico, D. Palumbo
ESIEE, Paris
September 1996
SPRA332
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CONTACT INFORMATION
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(281) 274-2320 |
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(281) 274-2324 |
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Contents |
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Abstract ........................................................................................................................... |
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Product Support on the World Wide Web .................................................................... |
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Introduction..................................................................................................................... |
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The Video Decoder ....................................................................................................... |
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Bitstream Scanning and VLC Decoding. .................................................................... |
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"Table-Look-At" Algorithm......................................................................................... |
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"Distributed Tree-Balancing" Algorithm..................................................................... |
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Decoder Architecture ................................................................................................... |
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Acknowledgments ........................................................................................................ |
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References .................................................................................................................... |
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Figures |
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Figure 1. |
Decoding Activities ........................................................................................... |
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Figure 2. Binary Tree Associated with the VLCs of Table 1 ............................................ |
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Figure 3. Data Structure of the "Table-Look-At" Algorithm .............................................. |
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Figure 4. Binary Tree Associated with the "Distributed Tree-Balancing" Algorithm......... |
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Figure 5. |
Decoder Organization : a) I Pictures and b) P and B Pictures (PH: Picture |
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Header; S: Slice). ............................................................................................. |
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Figure 6. |
VLC Decoding and IDCT+Reconstruction Statistics a) at 4 Mbitls and b) at 8 |
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Mbit/s ................................................................................................................ |
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Figure 7. |
Decoding Time for I, P, B Pictures vs. Bit-Rate................................................ |
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Tables |
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Table 1. |
VLCs for Some Pairs {run, level) ...................................................................... |
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Table 2. |
Processing Times for VLC Decoding (cycles/VLC) .......................................... |
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Table 3. |
IDCT and Reconstruction Processes: MVP-Cycles/Pixel for I, P, and B |
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Macroblocks ..................................................................................................... |
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Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP
Abstract
This application report presents the preliminary results obtained in the realization of the MPEG2 video decoder on the Texas Instruments (TIÌ) TM532OC80 MVP. We have addressed and solved the problems of bitstream scanning, variable-length code decoding, and inverse discrete cosine transform (DCT). The results obtained, integrated with preliminary work and available information about time requirements of image reconstruction for predicted and interpolated pictures, allow us to choose the architecture of the MPEG2 decoder. At present, it is possible to predict that a complete decoder will operate in real-time on one 50 MHz MVP for CCIR 601 4:2:0 sequences coded at bit-rates up to about 6 Mbit/s.
This document was part of the first European DSP Education and Research Conference that took place September 26 and 27, 1996 in Paris. For information on how TI encourages students from around the world to find innovative ways to use DSPs, see TI’s World Wide Web site at www.ti.com.
Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP |
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SPRA332
Product Support on the World Wide Web
Our World Wide Web site at www.ti.com contains the most up to date product information, revisions, and additions. Users registering with TI&ME can build custom information pages and receive new product updates automatically via email.
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Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP |
SPRA332
Introduction
The goal of this project, carried out in the framework of the TI University Elite Program, is to implement an MPEG2 video decoder 1, 2 on the TMS32OC80 MVP via the TMS320C80 PCbased Software Development Board (SDB).
The real time requirement is the critical point of the project and needs a careful analysis of the decoding process in order to assign the different activities to the available resources (e.g., master and parallel processors, on-chip memory, etc.).
In the sequel, after giving a short description of the decoder, we present the solution chosen for scanning the bitstream, decoding the variable length codes and for the inverse discrete cosine transform. The timings associated with such activities and with the reconstruction of the predicted and interpolated pictures3 will be presented.
Such data allows us to present an architecture that, in the case of CCIR 601 4:2:0 sequences, matches decoder activities with available resources for bit-rates up to about 6 Mbit/s on a 50 MHz MVP.
Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP |
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SPRA332
The Video Decoder
A schematic block diagram of the decoding process is given in Figure 1. For the sake of simplicity, only the reconstruction process associated with intracoded (I) and predicted (P) pictures is represented (z–1 denotes the delay between the reference and the predicted picture).
Figure 1. Decoding Activities
The process can be divided into the following main activities:
qLoading of the coded video bitstream from the external device (in our case the PC hard disk) into the C80 external memory. The coded video average bit-rate ranges from 2 to 16 Mbit/s for CCIR 601 sequences (video coded at 6 Mbit/s is subjectively perceived as fully equivalent to PAL).
qScanning of the bitstream. The bitstream combines both fixed length, which are to be searched and interpreted first, and variable length codes (VLC).
qDemultiplexing into overhead information (such as motion information: vc(n), quantizer stepsize: D(n), macroblock type) and quantized DCT coefficients: QC(n).
qDecoding of the variable length codes (VLC-1). In particular the VLCs associated to DCT coefficients are to be decoded into pairs {zero run length, level} according to the macroblock type.
qInverse quantization of the DCT coefficients (Q-1), saturation and reorganization from the zigzag scanning order to the natural (row-column) order.
qInverse discrete cosine transform (IDCT) of the DCT reconstructed coefficients and saturation.
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Implementing an MPEG2 Video Decoder Based on the TMS320C80 MVP |