The 50th-anniversary episode of the British television show was screened on 800 big screens in 20 countries at the same time as being broadcast on the BBC's channels.

【翻译】英国电视五十周年专题节目，在20个国家的800个大屏幕上，与英国广播公司频道同时被播放。

【分析】at the same time as看作固定搭配，意为动作“与......同时”发生，the same... as...“与......相同”，being broadcast为动名词的被动式。又如：

It's coincidence that we have the hardware failure at the same time as being ready to go live.  就在准备上线（也指电脑启动运行）的同时，我们遭遇硬件故障，这真是个巧合。

 刚才在“可可英语”网站看到该句的译文，只用一句话翻译完毕。感到莫名其妙：“英国电视的50周年庆的插播节目被20个国家的800个大屏幕在同一时间正在播出的BBC的频道所屏蔽。”——“被大屏幕...所屏蔽”？