Image Processing Reference
In-Depth Information
reduces the amount of hardware required and the implementation can be built in a more
distributed fashion.
There are issues with time stamping and the relevance of playing back stored inter-
active content, especially if it links to a networked connection. Any remote services that
were being accessed when the video was broadcast may not be available later when the
compliance-research request is made. These issues are also relevant for DVR-based sys-
tems that store multimedia for time-shifted playback.
Quite a lot of research still needs to be done in order to make recorded multimedia a
viable proposition.
Shape-Coded Embedding
Work is in progress to adapt the MPEG-4 Part 2 alpha-channel shape-coded video-com-
positing support so that it is also adopted by Part 10. This implies changes to the file struc-
ture with new atom types being introduced. The ordering of the macroblocks in the file
according to their decoding sequence will then need to encompass the alpha-masking
block decoding. Implementing a moving matte (see Figure 39-2) to composite one moving
image over another is then possible with the more compact H.264-coded video.
Using the shape-coded video and the still images as a background opens up the pos-
sibilities for providing some interactive controls to view the images as a slide show with
very little bit-rate overhead. Since the assets are already being delivered, the only addi-
tional coding overhead is a small button graphic and some script code.
Hidden Data Within the Video
Since the mid-1970s, broadcasters have been inserting more hidden information into the
video stream. Because of the bandwidth of the transmission system, there are limits to the
capacity of this hidden data. The text services use this to deliver their data in the lines that
are normally outside the visible picture area. Theoretically, there could be data embedded
in any of the lines that are not used for picture information. In practice only a few of them
are used.
Your video input circuits at the point of ingest may or may not allow this informa-
tion to be preserved. Some may blank out any lines that don't contain genuine picture
data. In that case you will not be able to use these data lines to assist your workflow. If the
data lines are preserved intact, then with the addition of some extra supporting code, your
workflow may exploit this data.
Teletext Signals
The most prolific data source outside the picture is the Teletext data feed. In the United
Kingdom and other countries, this provides a lot of useful data. For example, there
is a complete program listing looking ahead about 24 hours. There is “now and next”
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