Information Technology Reference
In-Depth Information
In addition to limiting the encoding load, if the streaming bandwidth required
from the server can also be limited then the streaming system can scale to large
numbers of users. This chapter presents a solution that can be employed when sev-
eral users are synchronously watching arbitrary regions of a high-spatial-resolution
video. It hinges on employing application-layer peer-to-peer (P2P) multicast for de-
livering the streams to the users. The solution exploits the commonalities in the
peers' regions such that they relay data to each other in real-time. This allows lim-
iting the bandwidth required at the server by making use of the forwarding capac-
ities of the peers. The main challenge is that user-interaction determines real-time
which regions are commonly wanted by which peers. The P2P overlay needs to
adapt quickly and in a distributed manner, i.e., peers take most of the action nec-
essary for acquiring the data they need, without much central intervention. Larger
dependence on central intervention represents another hurdle in scaling. The sec-
ond challenge is that peers can switch off randomly, taking away the resources they
bring with them.
Ideally, the changing RoI should be rendered immediately upon user input; i.e.,
without waiting for new data to arrive. If the client would delay the rendering until
new data arrive, the induced latency might hamper the experience of interactivity. In
both client-server unicast streaming as well as P2P multicast streaming, predicting
the user's navigation path ahead of time helps pre-fetch relevant sub-streams. The
more accurate the RoI prediction the lower is the percentage of pixels that have to
be error-concealed.
This chapter is organized as follows. Section 2 provides a sampling of interactive
streaming systems found in the literature. The goal is to highlight the challenges
as well as earlier proposed approaches for providing random access, enabling pre-
fetching and P2P design for other interactive applications that are similar in spirit to
IRoI video. Section 3 discusses several approaches for providing spatial random ac-
cess within videos. It elaborates one video coding scheme in particular. This scheme
builds a multi-resolution pyramid comprising slices. It is shown how background ex-
traction can be used to improve the coding efficiency of such a scheme. The trade-off
in choosing the slice size is also analyzed. The slice size can be chosen to strike the
right balance between storage requirement and transmission bit-rate. Section 4 de-
scribes variants of pre-fetching schemes. In one of the variants, the RoI prediction
is based on analyzing the motion of objects in the video in addition to extrapolat-
ing moves of the input device. RoI prediction can be carried out at the client, at
the server or collectively. Section 5 presents the P2P multicasting system in which
peers can control their individual RoIs. Key aspects of the design are presented that
enable peers to receive and relay respective regions despite the challenges outlined
above.
2
Related Work
This section draws on interactive streaming systems found in the literature. A brief
survey of the challenges in designing such systems and the solutions found in
