Decoding order recovery for multi flow transmission of scalable video coding (SVC) over mobile IP channels

Recent standardization activities for the transport of Scalable Video Coding over multimedia networking channels have introduced means to differentiate layers of a scalable media in transport. Therefore in RTP, those layers are transported in different RTP flows respectively RTP sessions. To decode such layers transported on different IP network flows, a decoding order recovery mechanism is required that reorders the media data of the layers to decoding order at the receiver or at an intelligent network element. Since today's multimedia networking channels typically provide presentation timestamps on the transport layer, it was obvious to rely on those data for decoding order recovery. Due to the fact that presentation timestamps do not appear in the media stream in increasing order, an algorithm purely based on presentation timestamps may fail in some scenarios where temporal scalability is used. Another approach to solve the problem is to use a numbering mechanism in the bit stream giving the decoding order. In this paper, we highlight both mechanisms as defined in the RTP payload format for SVC video and compare them in loss scenarios typically present in mobile broadcast channels. We show that the presentation timestamp based solution gives over a wide range of loss scenarios almost the same results in terms of decoded video quality as the numbering based approach.