Page 350 - Manual_Movie Edit Pro 2021_EN_Neat
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Incorrect field rate
If you move around the series of fields in a movie data stream you can see strong jitter
and flicker effects. Picture objects move in a backward movement - two steps
forwards, one back - since a delayed field is shown before the previous one. This can
happen in the processing chain if you export video material improperly with the wrong
field order and then import it into different material.
We use MXV or MPEG "Top field first" format for all analog recordings ("odd" in
other programs). DV-AVI on the other hand is saved with “Bottom Field First”.
P frames and B frames
P frames save only the difference between the current picture and the preceding I
frame. The "P" comes from the term "prediction" which describes this process.
B frames save the differences between the current picture and the I or P frame
preceding and following. This includes the information that was the same before and
remained the same after the current frame. Both directions are analyzed (indicates
the "B" in the name, i.e. "bidirectional-predicted"). You can read more under
prediction (view page 350).
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.
How does it work?
The encoder has a precisely defined GOP, for example IBBPBBPBB. This sequence is
transmitted together with the encoder, which always knows exactly which kind of
frame comes 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.
The first frame is always the I frame. It is completely encoded from the first picture.
Afterwards, the 4th picture is analyzed for the creation of the first P frame. (As
already said, the encoder, and later the decoder, will know that two B frames belong
between them.) This image will also be completely encoded, and afterwards all
macroblocks that haven't changed in comparison to the I frame will be deleted. They
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