X2

MPEG glossary 305
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for display in the arranger.
2. Incorrect field rate
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P frames and B frames
P frames save only the differe
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B
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Prediction
Prediction is a method of data reduction used by the MPEG format. The image elements
already known from the previous or following frames are removed from the data stream.
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ypical interlacing errors
ou can use so-called de-interlacing to avoid this type of artifact. De-interlacing places a
icture in between the two fields (interpolated). If you want to create stationary pictures
rom movies, then you should definitely use a de-interlace filter.
n the system settings ("File" menu -> Program settings) you can set the preview monitor
isplay to use hardware de-interlacing during video recordings for the video recorder and
f you move around the series of fields in a movie data stream, then you will see strong jitter
nd flicker effects. Picture objects move in a backward movement – two steps forwards,
ne back – since a delayed field is shown before the previous one. This can happen in the
rocessing chain if you export video material improperly with the wrong field order and then
mport it into different material. We use MXV or MPEG "Top field first" format for all analog
ecordings ("odd" in other programs).
V-AVI on the other hand is saved with “Bottom Field First”.
ou can correct the field series for each video object in its object settings. See: "Menu ->
ffects -> Object properties"
nce between the current picture and the preceding I frame.
he "P" comes from the term "prediction" which describes this process.
frames save the differences between the current picture and the I or P frame preceding
nd following. This includes the information that was the same before and remained the
ame after the current frame. Both directions are analyzed (indicates the "B" in the name,
.e. "bidirectional-predicted"). You can read more under
prediction (view page 305).
ow does it work?
he encoder has a precisely defined GOP, for example IBBPBBPBB. This sequence is
ransmitted together with the encoder, which always knows exactly which kind of frame
omes next. I, P, and B frames are differentiated.
Hint: When we talk about pictures, we mean frames of the video output, and I, P an dB
frames are the frames of the encoded video. Just as in movement approximation, blocks
(8x8 pixels) are united into macroblocks (16x16 pixels) during prediction.
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he first frame is always the I frame. It is completely encoded from the first picture.
fterwards, the 4th picture is analyzed for the creation of the first P frame. (As already said,