基于PTP协议的分布式解码系统视频输出同步的研究

Research on Synchronous Video Output of Distributed Decoding System Based on PTP Protocol

大型显示墙通常由多个LCD显示器拼接而成,或者由小间距LED显示模块拼接成大面积显示墙。这种显示墙的图像通常是按单个LCD或按一个特定LED区域输出驱动的,比如一块LCD屏或者一个分辨率为1920×1080的LED点阵区域对应一路HDMI输入,当一个视频图像跨越多个显示屏(或LED显示区域)时,为了保证图像质量,要求每个屏上的图像输出的是同一帧图像,并且要求各路输出的帧同步的相位也是同步的,否则就可能产生图像的“撕裂效应”,这种现象尤其在分布式解码系统上尤为突出并且难于解决。研究了如何在特定的嵌入式解码板上实现基于软件的PTP协议,以及在此基础之上如何实现解码板之间相同帧号的视频同步输出,并且保证各路视频帧同步的相位也基本相同,通过这两种同步的实现,可以完全消除图像的“撕裂效应”。

Large display walls are usually made up of multiple LCD displays spliced together,or made up of small-pitch LED display modules spliced into a large area display wall,with a display diagonal of several meters or even tens of meters.The image of this kind of display wall is usually driven by a single LCD or a specific LED area.For example,an LCD screen or a 1920x1080 LED dot matrix area corresponds to one HDMI input.When a video image spans multiple displays(or LED Display area),in order to ensure the image quality,the image on each screen is required to output the same frame of image,and the phase of the frame synchronization of each output is also required to be synchronized,otherwise the“tearing effect”of the image may occur.This phenomenon is particularly prominent in distributed decoding systems and is difficult to solve,because each decoder board in the distributed decoding system does not have a unified clock,and each decoder board adopts its own independent clock system.This article has studied how to implement the software-based PTP protocol on a specific embedded decoder board,and how to realize the video frame synchronization output between the decoder boards based on it,and ensure that the phases of the video frame synchronization of each channel are basically the same.Through the realization of these two kinds of synchronization,the“tearing effect”of the image can be completely eliminated.