Research On Interactive Technologies In Time Shift TV Systems

With the development of broadband networking and computing technology and the investigation of the Next Generation Internet(NGI),3G and 4G,the streaming media applications obtained more and more attentions.Both the internet service provider and the broadcast tv service provider introduced the IPTV services and the bidirectional digital tv services to enhance their occupation rate of the market.As one of the most important value-added service of the IPTV and bidirectional digital tv,the time-shift tv services are being widely studied by more and more researchers.The time-shift tv provide tv broadcast services to the users,meanwhile it gives the users the capability to choose pause,resume,fast forward,fast backward etc operations. This kind of capability changed the user's habits of watch the tv greatly.For a long time,the service pattern of tv broadcast was playing a programm at a fixed time and channel.The only choice of the users is watching it or not.The appearance of time-shift tv service is a milestone in the development of the internet and the digital tv.It brought the user's from the years of tv broadcasting to the years of interactive digital tv.This paper introduces the basic principles of time-shift tv to the readers,and then points out that the technologies of the time-shift tv in both IPTV and digital tv are in the same.Subsequently,we proposes a framework of time-shift tv according to the experiences of a practical project.The framework uses the broadcast tv data as its source,the STB as its terminal,the CATV or internet as its transmission medium.The interactive operation,which is the most important highlight features compared to the traditional TV services,is difficult to be deployed in practical projects because of its high requirements of resources.In this paper,we make a further research in the issues exists in the interactive operations.First we proposed a new localization method for the time in the time-shift tv systems,and then established a model for the VCR operations.Based on the model,we proposed two VCR implemental method:quality of perception based VCR-functionality implementation method and Scene Detection Based Scheme for Supporting VCR Functions.Both the methods we proposed can support the VCR operation in the condition that the bandwidth is fixed for the normal playback.The contributions of this paper are as bellows: ●A new time indexing method which synchronise the frame presentation time to the local machine time was proposed,and the PCR information was used to eliminate the colock frequency offset and drift between the receiver and the encoder.The proposed method supports:(a)smoothness switch between the muticast stream and the unicast stream based on the RTP protocol;(b)absolute time reference for the end user based on the indexing method.●Based on the investigation of the impact of the frame rate on quality of perception (QOP),an effective algorithm which selects the frames by cooperatively adjusting the frame rate and position was proposed.The proposed algorithm can effectively reduce the network bandwidth requirement of the VCR operation, while keeping better QOP.It outperforms the dual bit-stream algorithm,which only needs about 90 percent of the mean bit-rate bandwidth.●Based on the analysis of the reasons that the users choose the VCR operations, we introduced the scene-detection in to the implement method of fast forward operation,and then proposed a novel scheme based on the model of ff operation and the scene-detection.The scheme allocate the bandwidth for each scene based on its length,and select frames in each scene to be displayed dynamically.It can significantly reduce the number of redundant frames,so it can support the VCR operation in the bandwidth constraint width a very high frame rate and scene activity.