| 摘要 |
A decoder 2 decodes a first compressed digital video bitstream whilst preserving the compression parameters thereof, the compression parameters including a first buffer occupancy value VBV-1 representing the occupancy by the said first bitstream of a buffer of the decoder. A signal processor 40 processes the decompressed bitstream. An encoder 6 compresses the processed bitstream to produce a second compressed bitstream having a target bit rate, optionally with reuse of the said compression parameters of the first bitstream, the second bitstream having a second occupancy value VBV-2 representing the occupancy of a downstream decoder buffer by the said second bitstream. The encoder controls (i) the target bit rate of the second bitstream and (ii) the recoding of the second bitstream to meet the said target bit rate, the target bit rate being varied in dependence on one or both of (a) VBV-2 and (b) the difference between VBV-1 and VBV-2, and the degree of reuse of the said preserved parameters being varied in dependence on one or both of (a) the degree to which VBV-2 tends towards underflow and (b) the degree to which VBV-1 differs from VBV-2 tending towards underflow. In addition, stuffing bits are added to the bitstream if VBV-2 is tending towards overflow of the downstream buffer and/or VBV-2 differs from VBV-1 tending towards overflow.
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