L64005 MPEG-2 Audio/Video Decoder Technical Manual
4-1
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
Chapter 4
Video Data Flow
This chapter describes the MPEG bitstream construction, parsing, and
error handling as well as the operation of the channel buffer. This chapter
is divided into four sections:
4.1
Overview
The L64005 decodes MPEG-1 or MPEG-2 bitstream syntax and gram-
mar. A complete grammar description is found in the MPEG-1 specica-
tion (ISO/IEC 11172) and the MPEG-2 specication (ISO/IEC 13818).
In general, some limited error detection is possible in the syntax and
grammar parsing of a MPEG bitstream. In particular, illegal transitions
out of variable length code trees and illegal grammars are easily
detected. However, it is inappropriate to continue parsing the bitstream
after the rst error in a given layer has been detected, because the error
can propagate as far as the next start code (resync code). Resync codes
and coding layers exist to limit the propagation of errors. A given imple-
mentation must increase the number of resync codes (in particular,
increase the number of Slice Layers) to decrease the propagation of
errors. The L64005 therefore takes the approach of “damage control” in
response to channel errors, regardless of their source. The channel
switch time can be decreased by increasing the number of sequence
start codes in the stream.
4.2
Channel Data
Parsers
The L64005 parses the bitstream in two phases: pre-parsing and post-
parsing. The byte-wise pre-parser operates on data before it is written to
the channel buffer. The symbol-parallel post-parser operates on data