| Digital Multimedia Broadcasting(DMB)has the characteristics of wide coverage,large capacity,and the ability to publish information to large number of terminals at the same time,which can effectively make up for the shortcomings in the communication network that are easily blocked at certain times.However,due to DMB's bandwidth limitations,the low assignable bit rate and the lack of a return mechanism when pushing video services,it is difficult for DMB's current single description encoding direct push scheme to achieve the correct reception of video files by the receiving terminal within a short period of time,resulting in a significant increase in video playback delay.To address the above issues,this paper adopts a multiple description encoding technology that aims to prioritize a lower quality but acceptable video on the receiving end for a shorter period of time,in order to reduce the video buffering time on the receiving end and improve the user experience level.The main tasks are as follows:1.A multiple description coding method that can be adapted to DMB systems is proposed.The technology of multiple description coding is introduced,and corresponding improvements are made according to the characteristics of the DMB system.The original video is decomposed into two video components with a high resolution and a low resolution,which shortens the blank period from receiving the first video packet to starting to play,and improves the user experience.2.Aimed at the improved multiple description scheme,the DMB video push system was optimized accordingly.At the transmitting end,a large file segmentation pushing method is used to reduce the packet loss during the pushing process.At the same time,a cross-push scheme of two video components is designed to shorten the waiting blank period at the receiving end.At the receiving end,a scheme to restore and play back the two received video components and a technique to merge them to reconstruct the original video are studied.3.Using the laboratory's DMB system to set up the test platform,the entire solution was tested for performance and functionality.The test results show that:(1)the video effect played by the receiving terminal basically satisfies the low-quality video < highquality video < synthetic video ? original video in the subjective quality assessment,and the average PSNR values of low quality video and synthetic video in the objective quality assessment are greater than 25 d B and 35 d B,and the average SSIM values are greater than 0.85 and 0.95,respectively,achieving the expected effect;(2)the DMB video encoder and push system designed in this paper can realize the correct coding,pushing,receiving and playing of video data;(3)compared to the original video push method without multiple description coding,for the typical video files within 100 MB and 512 kbps DMB service channel,the time for receiving terminal to play low-quality video is reduced by 72.24% on average compared with the original video direct push scheme,which meets the expected requirements. |
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