B-frame
The use of bi-directional differential-coded frames ( Bidirectionally predictive-coded ) is a patented method in the digital video compression . These are individual images (English frame ) that are described by the difference to the preceding and following individual images (- a so-called delta coding , from both temporal directions - i.e. bidirectional), a type of so-called inter-images . In contrast to the second type, the P-pictures (English predictive-coded frames ), which only use previous pictures, an even higher proportion is described by reference to picture data already present in another single picture, which results in a further reduction of the required Amount of data results, whereby ultimately better compression rates can be achieved. The use of picture prediction results in groups of interdependent coded pictures each with at least one independently decodable picture, the intra- or key picture - the so-called group of pictures (GoP). Newer methods such as H.264 can also select the prediction type of the image differently for partial images. In the H.264 example, this results in so-called B-slices based on macroblocks .
B pictures found for example in MPEG - codecs and VC-1 application.
disadvantage
When streaming , it should be noted that intra- or P-pictures that follow B-pictures must be transmitted before them. Again, this is based on the fact that B-pictures use information from previous and subsequent I- or P-pictures. This results in the further disadvantages of the need for larger buffers and thus also greater delays inherent in the process in the transmission. If the prediction is based on both the previous and the following picture and an average is generated, the computational effort also increases with the use of B-pictures.
See also
swell
- ↑ Frank Gadegast: MPEG FAQ: multimedia compression, part June 3 , 1996, accessed on October 4, 2010 (English).