A High Quality Real Time VBR MPEG-2 System For Broadcasting Appucations

A high quality variable bit rate (VBR) MPEG- 2 encoding scheme that offers optimum video quality and bandwidth allocation is presented. The proposed scheme is very easy to implement and offers a very efficient real time VBR solution for broadcasting applications that involve multiplexed distribution of multiple video sources. A High Quality Pseudo VBR MPEG Encoding Process The advantage of variable bit rate (VBR) video over constant bit rate (CBR) is that it preserves picture quality regardless of the video content and offers optimum bandwidth allocation so that a potentially greater number of multiplexed VBR streams may be transmitted over a given bandwidth. Several different implementations of statistical multiplexing of multiple video sources and optimization of bandwidth allocation using VBR streams have been reported in the literature. However, the generation of VBR streams has not received the attention it deserves. In many cases, VBR streams are either obtained by using fixed quantization levels and multiplexing controllers or by assuming multi-layer implementations of the MPEG compression standard. These "non-true" VBR streams do not depend entirely on picture quality and thus do not closely represent the VBR distribution that is found in actual broadcasting applications. In video production and real-time broadcasting applications, rapid scene changes and excessive motion increase the differences between consecutive frames and as a result have a very negative impact in the perceived quality of the video. To overcome this problem, adjustment of the "standard frame sequence is necessary in order to accommodate for the extra information needed to accurately represent drastic changes between adjacent frames. We developed a method which automatically adjusts the frame sequence and the number of bits needed to represent each frame depending on the video content. The result is a significant improvement in video quality. Our method uses a large 30 frame GOP which allows for efficient redistribution of bits while introducing maximum delay of three frames. Redistribution of bits is based on a "smart" combination of SNR, quantization and motion activity information for each frame. Large 30 frame GOP's tend to have a significant number of low motion frames which are "starved" by ow algorithm thus saving bits for more active frame sequences. In addition, I frames are forced by our method on scene cuts thus introducing more than one I frame within a GOP and preventing long propagation of impairments due to rapid changes. Although the bit rate can be kept constant for every GOP, the increase of the GOP size in combination with our smart redistribution of bits generates a pseudo VBR stream effect which results in considerable improvements in video quality. Performance evaluations have shown that for the same picture quality our method improves the compression rate by at least 25%. The video streams generated by our encoder were successfully played back by all the existing hardware and software MPEG-1 and MPEG-2 players. A Real Tie VBR MPEG.2 System