If you can't determine which cyl/rod is knocking by the 'plug' test... Chuck that video into a edit program, separate out the sound track and 'zoom in' to the timeline till you can see the 'Knock' sound and it's pattern, then look closely at the video track to locate what position everything is in, in relation to the knock.
That and the plug test should get you closer to determining which cyl it is....
