The prominence of digital video on the Internet is rising constantly. Faster Internet connections and more powerful devices make video streaming over the Internet more and more popular. With mobile devices, however, the usability of digital videos that are streamed over a wireless network connection is still limited by the available resources. Mobile devices are often not capable of receiving and decoding high quality video streams from the Internet because of their limited resources as well as due to the limitations of a wireless network connection. The presentation, for instance, of a video stream with 1920x1080 pixels on a screen with a resolution of only 320x240 pixels is not possible without a high amount of processing power at the receiving device. The transmission of such a high quality video stream over a wireless link may additionally consume a large part of the available network capacity, which then may interfere active network connections of other devices. A limited network capacity may additionally prevent the device from decoding and displaying the video stream at all. One solution of these problems is to perform an adaptation of the video stream to the requirements of mobile devices during the transmission of the stream to the client.
In this work we investigated different protocols and mechanisms that allow for dynamic adaptation of video streams to the requirements of mobile devices. Therefore, we developed a multimedia gateway system that provides video adaptation during the transmission of a stream to the client. This gateway system is working completely transparent for the user because the gateway can be discovered automatically by the client. For the process of video adaptation itself we concentrate on compressed domain video transcoding mechanisms that avoid a time-consuming complete decoding and encoding of the video stream.
An adaptation of solely the spatial resolution of the stream is typically not sufficient to meet the requirements of the requesting device. On the contrary, the spatial and the detail resolution may also need to be updated. Existing approaches, however, are mainly restricted to the adaptation of only one of these aspects. In this work we investigated the impact of different adaptation dimensions on the visual quality of the adapted stream. Based on these results, we were able to give a clear recommendation for a multidimensional adaptation of video streams. To be able to perform such an adaptation of video streams, we developed a novel transcoding architecture that facilitates a smart combination of existing one-dimensional transcoding mechanisms. By the use of this video transcoding approach at the proposed gateway system, individual and dynamic video adaptation services can be provided to mobile devices.
... to be published in 2010 ...