
L64005 MPEG-2 Audio/Video Decoder Technical Manual
6-19
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
of Group 7 Register 26 are positive, then the reconstructed picture is off-
set to the right by
. If bits 7:2 of Group
7 Register 30, and if bits 2:0 of Group 7 Register 9 are positive, then the
reconstructed picture is panned up by
.
If the above values are negative, the direction of the pan is reversed. This
allows a small reconstructed image to be displayed at a selected location
on a larger displayed area. Regions outside the reconstructed image pic-
ture area can be set to any bitmap values under software control, or can
be masked by the OSD overlay.
To enable horizontal pan and scan to 1/8 pixel boundaries, use the Pan
& Scan 1/8 Pixel Origin eld in the Group 6 Pan & Scan Control Register
to change the start phase of the horizontal interpolation lter.
6.7
Display Trick
Modes
The L64005 can support two picture freeze modes: freeze frame and
freeze eld. When the user requests a picture freeze, the display control-
ler freezes in the requested mode and picture reconstruction stops at the
next eld boundary regardless of parity. When the user requests that the
video continue, the decoder starts again at the next eld. Users must
also request a Decode Stop for reconstruction to stop during the freeze
operation.
6.7.1
Trick Mode
Decoding
MPEG-2 supports a variety of trick modes that are signalled in the Sys-
tem Layer. The L64005 implements trick modes under control of the host
controller using the decode start/stop and freeze frame/eld features.
6.7.1.1 Fast Forward
The encoder or digital storage medium (DSM) sends selected I pictures,
or slices of I pictures, without the intermediate pictures to achieve fast
forward. The L64005 decodes such pictures without any special interven-
tion by the host controller.
6.7.1.2 Freeze Frame
Stop the decoder and select the display of either eld or the whole frame
to achieve freeze frame. Selecting eld freeze displays the same data in
both elds of the frame.
Figure 6.11 shows an example of freezing a frame for one frame time. In
this example, frame B2 is displayed in eld times O3/E3, and then using
wordoffset
8
×
() byteoffset
+
blockoffset
8
×
() lineoffset
+