Okay. I did some additional testing. I went in and disabled ALL my chrome extensions except for ABP. While I was at it, I went in to chrome://plugins and disabled all plugins except for Native Client. (Don't know what that is, but it sounds important!).
I am running Kaspersky Internet Security 220.127.116.1151, but I long ago disabled the extensions it loaded during its install; just to be safe, I disabled Kaspersky while I was testing the ABP problem.
With the above all in place, the problem still occurs, that is the video starts from the example link I provided (http://testtube.com/dnews/why-short-men-live-longer
), with audio playing properly but no video. I can tell that ABP is active as it does remove the 15-second lead-in ad video, as the audio goes straight to the podcast video clip.
I also enabled the "Allow in cognito" mode Chrome option for the ABP extension, and tried the experiment in Chrome's cognito mode. Same result.
And again, I want to point out the ABP used to work on the testtube.com site: it just stopped working several weeks ago. It took me a while to even identify that it was ABP that was the problem.
Don't know if this tells you anything, but when I use the AdBlock extension (version 2.6.34) instead of ABP, it works properly. Don't know if AdBlock is affiliated with you guys from ABP.