I mentioned recently that the BBC’s 2006 10-part documentary series on World War I was available on YouTube. Helpfully, someone has also uploaded the 26-part documentary series The Great War that the BBC created in 1964 to mark the 50th anniversary of the start of World War I.
https://www.youtube.com/playlist?list=PLu7g1OfsO2vcKnzSXQiCHisyUIQcclbxr