
1-28
Introduction
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
1.6.8.2 Program Change
If the coded data in the channel is changed to a new program source,
the system controller must inform the bitstream parser to stop decoding
and search for a new intra-frame resynchronization point. The L64005
then freezes on the last complete anchor frame until a new sequence is
acquired. Program acquisition time is a function of the encoder sequence
header length. B frames with a broken link are decoded unless the sys-
tem controller forces resynchronization. The system controller restarts
the L64005 when the channel buffer reaches an adequate threshold.
1.6.8.3 Virtual Program Channels
A seamless switch between virtual program channels may be achieved
if the different channels within a channel group have a temporally aligned
group of frame headers. Virtual channel switch is a function of the chan-
nel demultiplexer in the decoder. The L64005 handles virtual channel
switching such as a regular P frame to I frame transition in the bitstream.
Note that in a virtual channel scheme, no B frames can cross over the
group of frames boundary; these would constitute a broken link in the
new group— which would lead to a discontinuity in the video or depletion
of the channel buffer. Constraining B frames in a virtual channel scheme
is a function of the encoder. The system controller can freeze the display
if the channel becomes depleted because of a channel switch.
1.6.8.4 Channel Panic Modes
The channel buffer has no explicit panic modes, because it is generally
not dened where buffer thresholds should be set. If the channel buffer
underows, the L64005 can optionally interrupt the external controller
and then instigate a freeze frame. If the channel buffer overows, the
L64005 generates an interrupt. The typical recovery mechanism is iden-
tical to a channel switch; that is, the decoder freezes after the last good
frame, the broken frame is discarded, and the decoder is set to resyn-
chronize on a new group of frames. In a system with a properly matched
encoder and decoder, panic modes are not necessary.
1.7
Features
This section lists supported features and discusses their application.
Provides a highly integrated, studio quality MPEG-2 audio/video
decoder solution.