AN1482 ST Microelectronics, Inc., AN1482 Datasheet - Page 3

• Manufacturer Part Number: AN1482
• Description: Mpeg2 Main Profile Video Decoding on St100
• Manufacturer: ST Microelectronics, Inc.

1 - OVERVIEW ON MAIN PROFILE DECODING
Figure 1 : Main Profile decoder block diagram
Figure 1 shows the block diagram of the Main Profile decoder [1]. The basic building blocks are the same
as for Simple Profile, but some additional features are supported in Main Profile. In particular, Main Profile
defines a new type of pictures, called B (bidirectionally interpolated), that are predicted from past and
future I/P images. This implies an increased complexity of the Temporal Prediction block to support
bidirectional prediction.
A Main Profile decoder must support all the prediction modes (up to six) and the two possible picture
structures (frame pictures and field pictures).
Block IDCT/Add Prediction can be performed either in field or frame mode.
The corresponding bitstream parser, represented by the block headers and motion vectors decoding ,
must be able to support the syntax corresponding to the above features.
Huffman decoding must support MPEG-1 backward compatibility (two special routines have been added
for this, since MPEG-1 syntax uses different escape codes) and two types of coefficients scan (zig-zag
and alternate).
The following chapters depict all these basic blocks, showing their performance on the optimized
assembly implementation for ST120. However, the reference C source is the one developed by the
MPEG Software Simulation Group [2].
M
B
S
R
E
A
T
T
I
quantization/inverse
Headers and motion
decoding/inverse
vectors decoding
Huffman
scan
FRAME BUFFER
Prediction
Temporal
IDCT
AN1482 - APPLICATION NOTE
Prediction
Add
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