SMART: Off-road Video Streaming

Li Shipeng, Internet Media Project Manager.

SMART, is the acronym of Scalable Media And Robust Transport, an original "variable scale" video project (scalable ), that makes it possible to transmit videos continuously online using changing networks, without the image quality suffering from the sort of sudden drops in the video data transfer rate that are so common in today's Internet connections. Using the current Real Networks and Windows Media technologies, these slowdowns are often the cause of significant deterioration in image quality and may be covered with black spots or shrouded in digital noise. This can even happen where a user has calculated the average constant transfer rate for the connection and most of the video sequence has been saved to the buffer memory.

To avoid these problems, Li Shipeng and his team have shown great ingenuity. First of all, they have opted for a variable bit rate, whereas most current systems rely on a constant, pre-calculated bit rate. Above all, they have perfected a two-stage transmission system, which first sends the main frames and only subsequently the intermediate frames. Mpeg compression technology is based on the detection of "key" images in a video sequence, i.e. an average of one frame in five. These images are compressed and stored as a whole; then all that has to be done is to code the changes into the subsequent images, based on the key images.

During the mpeg transmission stream, a key frame is fed, followed by information about the changes to subsequent frames, then comes a new key frame and so on. But should there be a reduction in the bit rate or an interruption of a fraction of a second during transmission of a key frame, the image will irrevocably deteriorate. Using SMART, all of the key frames are sent at the start of transmission, with a parity control that will show whether they have reached their destination, so that, if necessary, any missing frames can be resent. Only then are the intermediate frames sent, with greater or lesser detail depending on the actual bit rate at the time of sending. This means that if certain frames are lost on the way, the image is only slightly degraded because these are just the intermediate frames. It's as simple as Christopher Columbus's egg!

The following slide show gives an idea of the quality improvement obtained. Once it has acquired a DRM, (Digital Rights Management) layer, SMART will be bundled with Windows. In view of its intrinsic qualities and Microsoft's commercial clout in this type of market, we think it won't be long before this technology is used throughout the huge world network.