Research On Algorithms And Optimization Of An Embedded Dual-Stream Video Encoder

Video Encoder is required to produce dual-stream with different resolutions due to the limit of network bandwidth in video surveillance. One stream with high resolution is used for local storage, the other stream with low resolution is used for transmission through the network. Or one with high resolution for transmitting through wireline network, and the other through wireless network to support access of mobile devices such as mobile telephones. Usually, a dual-stream video encoder engages two separate encoders to code the same video. It is obviously that it doesn't consider the correlation between the two streams and cause a lot of recalculations. Thus it is very important for the dual-stream encoder to increase its efficiency by making use of the correlation between the computation of coding the two streams.Motion estimation is the most time-consuming part in the video coding process. By imitating motion vector reuse methods in video transcoding technology, a method named as dual-prediction refine algorithm is proposed to obtain the motion vectors for the low resolution coder core. It tries to reuse the motion vectors which were already obtained by high resolution coder core for avoiding redundant computation to get the motion vectors. The reuse process of the motion vectors consists of two steps. First, the motion vectors for the low resolution coder core are composite of the motion vectors obtained by high resolution coder core, in the meantime, a predicted version is also generated by using the motion vectors of the left, up and up right neighbours for each macroblock. Then, the difference between the predicted motion vectors and the composite motion vectors is used to decide whether the refinement of the motion vectors is needed, to further improve the precision of the composite motion vectors. The refine treatment is conducted in a search window within only four pixels. Thus, a good trade-off is gotten between the precision of the motion vectors and computing time. A dual-stream video encoder with CIF and QCIF resolutions is implemented on TI DM642 platform. Many methods such as compiler option optimization, data pack, intrinsic functions, loop Unrolling, linear assembly are used to optimize it.The experimental results show that the speed of the low resolution coder core of the dual-stream video encoder increases by about 50% through reusing the motion vectors. And the PSNR of the compressed video is improved about 0.3 to 0.5dB averagely after using dual-prediction refine method to do the refine treatment. The optimized dual-stream video encoder could run faster about five times than original one.