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Introduction
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
the encoder clock so that local time base correction is unnecessary.
However, with 10 ppm accuracy in the encoder and 50 ppm accuracy in
the decoder, the decoder and encoder may drift by as much as one
frame every 9 minutes, so some form of correction is clearly desirable.
1.6.3.8 Vertical Blanking Interval
Data stored in the frame stores can be output during the vertical blanking
interval. This data does not constitute part of the MPEG image, but it can
be downloaded by the user, and can be used for optional features such
as VITS and closed caption.
1.6.4
On-Screen
Display
The L64005 integrates a exible on-screen display controller that allows
the overlay of text and graphics on top of the decoded video. The overlay
is digitally mixed with the decoded video immediately before it is output
on the video port. The overlay data is always displayed at the same size
regardless of the resolution or mode of the video data. Pan and scan of
the video data does not affect the position of the overlay data. Two basic
modes supported for the overlay data are:
Up to 720 x 576 pixels at 2 bits/pixel
Up to 720 x 576 pixels at 4 bits/pixel
A color expansion feature and color palette allow for exibility in color
selection. In addition, various sub-formats can be supported, including
240 line operation which presents a full sized icker-free image.
1.6.5
Audio Decoder
The L64005 integrates an MPEG audio decoder, capable of decoding
two audio channels at bit rates of up to 448 kbps. The decoder operates
at MPEG Layer 1 or Layer 2 only.
1.6.5.1 Input Buffering
The L64005 provides for an audio channel buffer (rate buffer) as part of
the attached DRAM store. This offers considerable savings over separate
audio decoders which need an additional DRAM for channel buffering
when operating in conjunction with a video decoder. The audio channel
buffer is maintained separately from the video channel buffer.