The Unpredictable Certainty White Papers (1997) / Chapter Skim
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An SDTV Decoder with HDTV Capability: An All-Format ATV Decoder
An SDTV Decoder with HDTV Capability: An All-Format ATV Decoder
Pages 67-75
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From page 67... ...
The bit streams were decoded according to the concepts described herein, including pre-parsing, the effects of reduced memory sizes, simplified IDCT processing, and the various associated filtering steps. The pre-parser and resampling result in a certain amount of prediction "drift" in the decoder Hat depends on a number of factors, some of which are under He control of the encoder.
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From page 68... ...
An HDTV decoder Will also require at least ~ MByte of RAM for channel buffer memory to provide temporary storage of the compressed bit stream. It can be expected that practical HDTV video decoders will employ 12 to 16 MBytes of specialty DRAM, which Will probably cost at least $300 to $400 for the next few years and may be expected to cost more than $100 forge foreseeable fixture.
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From page 69... ...
The weights used in this operation depend on the full-precision motion vectors extracted from the coded bit stream. Experiments have shown that it is Important that the prediction downsampling process is near Me inverse of the upsampl~ng process, since even small differences are made noticeable after many generations of predictions (i.e., after an unusually long GOP that also contained many P-frames)
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From page 70... ...
~ ..~.. Active Active H Scale V Scale Downsampled Horizontal Vertical Factor Factor Horizontal 1920 1,080 3 1280 2 640 2 Downsampled Vertical 540 3 2 # Frames Stored Downsampled Memory Required 12,441,600 5,529,600 Free Memory With 16 WITS DRAM 4,335,616 11,247,616 NOTE: Shaded row reflects SDTV format for reference.
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From page 71... ...
The pre-parser only discards fills MPEG code words, creating a compliant but reduced data rate and reduced~uality bit stream. The picture degradation caused by the pre-parsing operation is generally minimal when downsampled for display at reduced resolution.
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From page 72... ...
In the enhanced SDTV decoder outlined in this paper, the decoder can accept bit streams intended for a much larger buffer (i.e., an HDTV bit stream) and can perform its own triage on the incoming bit stream to maintain correct buffer occupancy.2 This pre-parser is an additional cost over a stand-alone SD decoder, but the cost and complexity are low since it can run at the relatively low average incoming-bit rate.
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From page 73... ...
Complexity Comparisons A block diagram of He HD-capable video decoder is shown in Figure 2. This can be compared wig Figure 13 C`SDTV Video Decoder Block Diagram33' to identify the additional processing required over an SD decoder.
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From page 74... ...
Some of the bit streams used for testing were encoded by the authors using their MPEG-2 MP~HL software; others were provided by Thomson Consumer Electronics. Decoding at HDTV was done using the authors' MPEG-2 MP~ software.
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From page 75... ...
The resulting HDTV and downconverted images were examined and compared. Although the downconver~ images were of discernibly lower quality Han the decoded full-HDTV images, observers agreed that the downconversion process met perfonnance expectations of "SDTV quality." CONCLUSIONS This paper describes an enhanced SDTV receiver Hat can decode an HDTV bit stream.
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