| Summary: | 碩士 === 國立交通大學 === 電子研究所 === 83 === A source coding algorithm based on MPEG-1 standard is proposed
for home-use digital VCR. To meet the requirement of high speed
playback of DVCR, the encoded IBP unit data is divided into IDC(
independent decodable code) and DDC(dependent decodable code)
parts. The IDC part contains the DC and low frequency
coefficients of I-frame that can restore low resolution
pictures for trick play. For normal play, both IDC part and DDC
part are necessary to reconstruct the full resolution pictures.
In order to update each segment of a picture frame
contiguously, a new data distribution scheme is invented for
variable speed playback. Because each tape track can only store
a fixed amount of data bytes, it becomes very critical to have
a precise control on bits allocation. An essential element in a
high performance buffer/quantizer control scheme is the bits
model that estimates the compress bits when a certain
quantization stepsize is in use. Hence, we develop an adaptive
piecewise linear bits estimator whose structure is similar to a
tree-structured piecewise linear filter. Each node in the tree
is associated with a linear relationship between macroblock
bits and activity/stepsize. The parameters in the relationship
is adjusted by a modified LMS algorithm. Computer simulations
show that this buffer/quantizer control algorithm and the tape
data distribution scheme produce a quite good overall
performance. Under the precise control of bits distribution,
this system not only provides the uniform picture quality at
normal speed playback, but also it offers acceptable quality at
high speed playback.
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