EM8476 데이터 시트보기 (PDF) - Unspecified

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EM8476

MPEG-4 Decoder for Set-top, DVD and Streaming Applications

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EM8470, EM8471, EM8475, EM8476

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.

Sigma Designs, Inc.

355 Fairview Way • Milpitas, CA, USA 95035 • Tel: 408.262.9003 • Fax: 408.957.9740

www.sigmadesigns.com • sales@sigmadesigns.com

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