1-4
Introduction
1.2.1 Video Decoding
The L64021 complies with MPEG-2 Main Prole at Main Level standards
(ISO 13818-2). It operates optimally at image sizes up to 720 x 480
pixels, with a frame rate of 30 f/s for NTSC, or 720 x 576 at 25 f/s for
PAL. The L64021 can also decode MPEG-1 sequences. The coded data
channel can have a sustained bit rate of up to 20 Mbit/s. The L64021
also supports images with resolution lower than 720 x 480 pixels (see
Video Postprocessing Filters).
Images with resolutions below 720 x 480 pixels are interpolated to full
size using on-chip lters. This allows programming produced at different
resolutions to be decoded and displayed on televisions with standard
NTSC or PAL timing, and it allows the use of digital or analog NTSC or
PAL encoders operating at standard television frequencies (typically
27 MHz). In addition, the lters provide the capability to pan and scan
the MPEG image to 1/8-pixel accuracy. The L64021 also supports
letterbox display format with an integrated vertical lter for 3/4 decimation
(720 x 480 images are decimated to 720 x 360 pixels).
The L64021 integrates an on-screen display (OSD) controller capable of
overlaying an image up to 720 x 480 pixels (720 x 576 for PAL), at up to
8 bits/pixel, on top of an MPEG video sequence while it is being
decoded. In addition, the L64021 contains an on-chip Subpicture Unit
(SPU) decoder for cost-effective integration of the graphics function. The
SPU decodes the bit map for graphic overlay and executes SPU
instructions so the graphic display can be changed on the y without
CPU intervention.
1.2.2 Audio Decoding and Formatting
The Audio Decoder module contains a Dolby Digital Decoder, an MPEG
(Musicam) Decoder, a Linear PCM Decoder, a Dolby Digital Formatter,
an MPEG Formatter, a DTS Formatter (L64021D only), an Audio DAC
Interface, and a S/P DIF (IEC958) Interface. The MPEG Decoder can
decode two channels of MPEG (Musicam) audio Layer I or Layer II over
the full range of compliant bit rates and sample rates. The Dolby Digital
Decoder decodes multichannel Dolby Digital streams and downmixes
them to two channels of audio output. The audio decoders use the same
external memory device as the video decoder for its channel buffers. The
host controls the mode of the Audio Decoder module; that is, it
determines which decoder runs and where its output goes, as well as
which formatter runs.