Metadata consumption at the proxy

Multimedia adaptation is a key technology for

assuring the quality of end-to-end delivery in the

network. Adaptation can dynamically react on

different kinds of presentation devices and on

unpredictable resource availabilities. Proxy

servers situated in the middle of the delivery

chain constitute an ideal place to control multimedia

delivery and adapt the stream if resource

availability changes. In this context, we built the

Quality-Based Intelligent Proxy (QBIX), which is

a terminal capabilities- and metadata-aware

mapped (RTSP; http://www.rtsp.org) proxy server

that supports real-time adaptation in the compressed

(temporal adaptation only) and

uncompressed domains. Adaptation improves the

hit rate in the proxy cache and lets the proxy act

as a media gateway supporting transcoding in real

time based on metadata.9 One part of the metadata

is sent by the server and describes the video

variations (MPEG-7 VariationSet descriptions),

and the other part is provided by the terminal end

user (in the form of Composite Capabilities/Preferences

Profiles, which we describe later in this article) sending terminal capabilities to the proxy.

The proxy extracts the terminal capability

information from the video request and checks if

it has this music video in its cache in a quality

that matches the terminal capabilities. If the

video is already available, but its properties aren’t

in accordance with the terminal’s characteristics—

for example, the video’s bit rate is too high

to be consumed at the end user’s site—the MPEG-

7 descriptions that accompany the video are

examined by the proxy. They contain hints on

which variations of the original video should be

selected or created (if one doesn’t exist) to meet

the delivery and presentation constraints. These

hints contain the video’s expected size, bit rate,

and quality. The proxy then chooses from among

these variations the one with the highest quality

that meets the restrictions of the end user’s terminal.

The proxy can either load the required

variation from the server or generate it with a

sequence of appropriate transcoding procedures.9

We implemented metadata consumption at the

proxy and the terminal using our Video ToolKit

(ViTooKi). ViTooKi is principally a set of libraries

that support adaptive standard-compliant video

streaming, transcoding, and proxy caching. It supports

MPEG-1/2/4/7/21 and MP3/AAC file types,

stored in various containers like mp4 and avi using

standard protocols with retransmission and the

server, proxy, and player included.