85 How does MPEG syntax facilitate parallelism ? (MPEG-2)
Description
This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
85 How does MPEG syntax facilitate parallelism ? (MPEG-2)
For MPEG-1, slices may consist of an arbitrary number of macroblocks.
They can be independently decoded once the picture header side
information is known. For parallelism below the slice level, the coded
bitstream must first be mapped into fixed-length elements. Further,
since macroblocks have coding dependencies on previous macroblocks
within the same slice, the data hierarchy must be pre-processed down to
the layer of DC DCT coefficients. After this, blocks may be
independently inverse transformed and quantized, temporally predicted,
and reconstructed to buffer memory. Parallelism is usually more of a
concern for encoders. In many encoders today, block matching (motion
estimation) and some rate control stages (such as activity and/or
complexity measures) are processed for macroblocks independently.
Finally, with the exception that all macroblock rows in Main Profile
MPEG-2 bitstreams must contain at least one slice, an encoder has the
freedom to choose the slice structure.
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