MASTER THESIS Video Watermarking - Computer Graphics Group ...

There are three types of slices: I, P and B. I slices are completely intra coded
(no reference pictures are used for prediction) while P and B slices use inter
coding, i.e. previous pictures in display order (and in case of B slices, following
pictures as well) are used for prediction.
Intra coding may provide access points to the video sequence where decoding
can begin and continue correctly, but typically gains only moderate compression
efficiency in comparison with inter coding.
The intra prediction process consist in exploiting of spatial statistical
dependencies in a single picture while the inter prediction process exploits
temporal statistical dependencies between different pictures. The prediction
processes are thoroughly described in Section 3.2.
Only the pictures that go in the stream before the current slice can be used
for prediction. Thus, even following pictures in display order used for prediction
should go before the current slice. The reason is simple: decoders need those
pictures to be able to decode predicted slices on-the-fly. Let us assume that each
picture consists of a single slice, then the difference between display and stream
order is illustrated in Figure 4 and Figure 5 (prediction dependencies are
indicated by arrows).
3.1.3 Macroblocks
Figure 4: Display order of pictures
Figure 5: Stream order of pictures
A slice is a sequence of macroblocks, as depicted in Figure 3. A macroblock,
consisting of a 16×16 block of luma samples and two corresponding blocks of
chroma samples, is used as the basic processing unit. Luma samples represent
luminance of pixels while chroma samples represent chromatic components.
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