Home > Archive > Compression > April 2006 > MPEG compression, how are frame types chosen?
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MPEG compression, how are frame types chosen?
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| niall.rea@gmail.com 2006-04-19, 7:55 am |
| How does an encoder chose whether an I, B or P frame should be used for
compression? The typical sub GOP or sub GOVs are generally IBBP, but
some encoders will give different numbers of B and P frames per
GOP/GOV. Does it depend on the amount of motion detected in the motion
estimation stage along with a user specified parameter? Thanks.
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| Jim Leonard 2006-04-19, 6:55 pm |
| niall.rea@gmail.com wrote:
> How does an encoder chose whether an I, B or P frame should be used for
> compression? The typical sub GOP or sub GOVs are generally IBBP, but
> some encoders will give different numbers of B and P frames per
> GOP/GOV. Does it depend on the amount of motion detected in the motion
> estimation stage along with a user specified parameter? Thanks.
Short answer: It is typical to restart a GOP when there is a scene
change (when a certain percentage of total picture information changes
from one frame to the next) so that B or P frames aren't "wasted"
trying to encode a completely new section of video. This would restart
the GOP, and GOPs begin with an I frame.
Long answer: Each compressor is different, so I can't give you a
longer answer :-)
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