Bit Allocation for Variable Bitrate Video

In this paper we propose a special bit allocation method which can be used in most rate control algorithms in variable rate video applications. In real-time video communication applications, we need a constant short-term average bitrate, while in variable bitrate applications such as streaming and local recording applications, a constant long-term average bitrate is sufficient and more short-term variation in bitrate is acceptable. In comparison with constant bitrate video, a variable bitrate video can provide better visual quality and coding efficiency for compressed video sequences. Furthermore, while more variation in bitrate is possible we have additional degrees of freedom to control the encoding parameters. We propose a special bit allocation algorithm to take advantage of this freedom in variable bitrate video. We introduce a new type of frame namely SPP frame (SPecial P frame) that can be used in combination with I, P, B and other types of frames in different encoders including H.263, MPEG-4 and H.264/AVC encoders. We propose a simple method to implement the SPP frames independently of the rate control algorithm. The experimental results show that the SPP frames can considerably increase the total average quality of variable rate encoded video