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EM8470, EM8471, EM8475, EM8476
- 9 -
Sigma Designs, Inc.
355 Fairview Way Milpitas, CA, USA 95035 Tel: 408.262.9003 Fax: 408.957.9740
www.sigmadesigns.com sales@sigmadesigns.com
Hardware vs. Software MPEG Decoding
Use hardware-based MPEG decoding when:
Delivery of audio and video to a television is the primary function of the system. Standard consumer-oriented connectors
for audio and video must be used, instead of PC-oriented break-out cables and mini jacks. (Example: set-top box.)
Home theater quality audio and video (such as 6-channel audio analog outputs, component YPbPr or RGB analog video
outputs and a SPDIF digital audio output) are required. Although specifications for audio and video solutions for the PC
market look good on paper, the products themselves rarely meet consumer expectations.
A relatively slow CPU, such as an embedded processor, is used to lower system costs. Slower CPUs also reduce power
consumption and eliminate noisy fans. Decoding full-screen MPEG-4 requires a 1 GHz CPU, which is currently far too
costly for low-cost set-top boxes to employ.
Multiple video streams must be decoded simultaneously to support picture-in-picture (PIP).
Ancillary data processing, such as copy protection, closed captioning (multiple languages), teletext (multiple languages),
v-chip (multiple regions) and widescreen signaling must be performed for each active video stream displayed. Wide-
screen processing must be able to handle anamorphic and letterboxed content for either 4:3 or 16:9 televisions. These
are typically overlooked in software-based solutions.
Alpha blending is required when overlaying text and graphics (such as closed captioning, teletext, EPG, OSD, etc.) over
video to avoid artifacts (such as flicker) when displayed on a television. Such artifacts are caused by the limited-band-
width video connection between the set-top box and television. It is typically implemented using anti-aliased fonts and
graphics.
High quality video scaling is required for large television screen sizes. Artifacts not noticeable on a small VGA monitor
are magnified on a large television.
Use software-based MPEG decoding when:
MPEG decoding is a secondary, rather than a primary function of the system. (Example: PC.)
MPEG decoding is used in a single-tasking environment. Since MPEG decoding requires substantial CPU resources,
using other applications usually affects playback quality.
A fast CPU is already available on the platform.
Only standard stereo audio and video (composite or VGA) outputs are needed.