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MPEG glossary
365
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MPEG glossary
Motion estimation
Motion estimation is a further element for reducing data used in MPEG
encoding.
Motion estimation also occurs in the B and P frames. The image difference
that still exist after prediction (view page 369) are examined. Complex
algorithms
are used to search for an original occurrence of the macro block
in the reference frame of each macro block of the P or B frame (these are
units of 2x2 blocks specially combined for this purpose), which have been
moved either by movement or by camera pan. They can then be left out in
the P and B frame. Only the information by how far and to where the macro
block has been moved is saved instead. This vector is called the motion
detector.
In the General encoder settings (view page 360), you can specify the quality
of
the final MPEG video. This factor also influences the time required for
encoding. The longer it takes, the better the quality.
Bit rate
MPEG is a format used for storage and transferring. With older formats (e.g.
AVI) you could predict that 20 seconds of movie would result in 20 MB of
data. The file size is this a direct measurement of quality.
This is different for MPEG: The amount of data available can be used
differently for different display modes. 20 MB can be 4 seconds of DVD
Video or 5 minutes Internet streaming in thumbnail format. The quality of an
MPEG video is measured by the width of the created data stream, the bit
rate. This is the amount of the transmitted data per time unit; it is stated in
kBit/s or bit per second.
Bits, not bytes are used, since the data word width has to address the
transmission restrictions.