Survey of Dirac: A Wavelet Based Video Codec for Multiparty Video Conferencing and Broadcasting - Intelligent Video Event Analysis and Understanding - page 223

5.3 Motion Estimat

tion and Motion Compensation

5.3.1 Temporal Predict tion Structures

Dirac encoder uses three t
a) Intra pictures (I p
These are cod
b) Level 1 (L1) and
Both of these
pictures
The difference between
predicted only (also know
predicted from both earlie
The Dirac software em
Each picture is encoded w
order, the picture number
the buffer. The decoder
buffer for the appropriat e
The decoder maintains a c
through the picture IO to
be a video player or may
with that picture numbe
eliminating pictures which
Nevertheless, the enco
number of L1 pictures bet
can be specified; and va
specific GOP structures. A
GOP structure is shown b

types of picture.
pictures)
ded without reference to other pictures in the sequence
d Level 2 (L2) pictures
e are coded with reference to other previously code ed

L1 and L2 pictures is that L1 pictures are forward
wn a P-pictures) whereas L2 pictures are B pictures ar
er and later references.
mploys a picture buffer to manage temporal predictio
with a header that specifies the picture number in displa
s of any references and how long the picture must stay i
then decodes each picture as it arrives, searching th
e reference pictures and placing the picture in the buffe
counter indicating which picture to 'display' (i.e. push ou
the application calling the decoder functions, which ma
be something else). It searches the buffer for the pictur
er and displays it. Finally, it goes through the buffe
h have expired [8].
oder operates with standard GOP modes whereby th
tween I pictures, and the separation between L1 picture
arious presets for streaming, SDTV and HDTV impl
A prediction structure for picture coding using a standar
below:

d-
re

n.
ay
in
he
er.
ut
ay
re
fer

he
es,
ly
rd

Fig. 10 Prediction of L1 and d L2 pictures when L1 pictures are P pictures [8]

I-picture only coding
Setting the number of L1
have a GOP, and that we
useful for editing and othe
required, but I-picture on
suitable support.

pictures to be 0 on the encoder side implies that we don
e're doing I-picture only coding. I-picture only coding
er applications where fast random access to all pictures
nly coding is not essential for these applications wit

n't
is
is
th