Limitations of multiple reference frames with cyclic intra-refresh line for H.264/AVC

Introduction: The H.264/AVC (Advanced Video Coding) codec has introduced multiple reference frames (MRF) for inter-prediction, in contrast to the single-reference frame of the earlier codecs such as H.263 version 1. In addition to the increased compression efficiency obtained by MRF, soon it was realised that MRF could also be used as a technique to prevent error propagation in video streaming systems with back channels as an alternative to inserting additional intra-coded data. Since MRF allows several reference frames (max. 15 frames) for prediction, when transmission errors occur in a frame, the decoder can signal back to the encoder that this frame should not be used for future prediction, hence preventing error propagation [1]. When there is no back channel, e.g. in 3GPP’s Multimedia Broadcast Multicast Service [2], MRF might still be employed [3] if temporal error drift can be reduced by placing intra-refresh (IR) macroblocks (MBs) alongside the normally inter-coded MBs of predictively-coded P-frames. One way to do this, with no loss of generality, is to place a line of intracoded MBs within each frame, with the position of the line cycling in a horizontal or vertical direction for each successive frame. Other IR patterns are also possible, e.g. as occurs in [4]. This Letter investigates the behaviour of MRF with a cyclic intra-refresh line over error prone channels.