Multimedia Web services for mobile clients using quality aware transcoding

Mobile applications will increasingly depend upon multimedia information originating in the web and attempt to access this data over wireless networks that are more expensive and slower than typical wireline internet access from desktops. Transcoding is an important technique that can allow network proxy servers to offer differentiated service by customizing the delivered object size for the network bandwidth available on the “last hop” to the mobile client. We exploit technology that we had previously developed that characterized the quality versus size tradeoffs in transcoding JPEG images. This technology supplies more information for use in transcoding policy decision making. We evaluate the performance benefits of incrementally incorporating this information in a series of transcoding policies. The principal contribution of this work is the demonstration that it is possible to use informed transcoding techniques to balance the need for good quality of multimedia content while reducing consumed network bandwidth and server CPU overhead. We show that policies that aggressively transcode the larger images can produce images with Quality factor values that closely follow the un-transcoded base case while still saving as much as 150 KB. A transcoding policy that has knowledge of the characteristics of the link to the client can avoid as many as 40% of (unnecessary) transcodings.