
8-20
System Stream Decoding and Synchronization
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
Note that if
SCRnew is updated at the exact time of arrival of the
ESCR, then the equation reduces down to following equation in the
unltered case:
;
if
, then
.
This routine completes clock recovery in the simple case. In a real sys-
tem, the SCR error is ltered to prevent oscillation and jitter on the SCR
value. For a system operating off of the PCR, the operation is basically
the same, except that the
SCRarr time is sampled at the arrival of the
PCR from the transport device.
8.5.2
Creating Audio
and Video PTS
list
When audio and video PES packets enter the L64005, they are parsed
and stored in the external memory buffer. This is the rst step in the
decoding process.The L64005 provides four separate regions for PES
data: the video PES header buffer, the audio PES header buffer, the
video channel buffer, and the audio channel buffer. The PES header buff-
ers store only the PES header information, and the channel buffers store
the PES payload or the actual compressed MPEG-2 data from the video
sequence level or the audio sync byte. All buffers are implemented as a
queue; that is, the start and end address of the buffers must be specied
externally, and each buffer maintains write and read pointers. All the
pointers, except for the read pointers to the Audio and Video PES header
buffers, are built into the L64005. External software should maintain the
Audio and Video PES header buffer read pointers.
Figure 8.9 shows how
the L64005 stores PES packets in the audio and video buffers.
SCRnew
SCRcurrent
ESCR
SCRarr
–
+
=
SCRcurrent
SCRarr
=
SCRnew
ESCR
=