There are three ways to block online videos in WFilter 4.1：
1. Block video websites by url libiary in WFilter 4.1 .
Please refer to: How to block video websites
2. Block all video files. It only block videos playing and does not block websites.
Please refer to: How to block all video files
3. Block video protocols. You can block protocols in ‘Streaming’ to block video webiste and client.
Please refer to: How to block video streaming protocols?