Design of switching frames for Constant Bit Rate video streams

To map the data rate to the available channel bandwidth, one method is to switch between video streams of different qualities using either intra (I-) frames or the switching predictive (SP-) frames of H.264. Due to its better coding efficiency SP-frames are preferred over I-frames, but these frames are generally exercised with variable bit rate (VBR) coded videos, therefore limiting their usage. For constant bit rate (CBR) coded videos, in which the quantization parameters (QP) are decided on the fly for every macro block, the design of SP-frames becomes difficult due to the multiple (twice) quantizations used in SP-frames. In this paper we propose to design SP-frames for CBR coded videos, selecting the QPs in such a way that the varying QP nature of CBR coding is preserved. The proposed algorithm is compared with the already implemented SP-frame concept for VBR video coding, showing that both the concepts have similar behavior