The early history of live TV recording is interesting. Does it give us another insight into the hoaxing of the Ruby-Oswald assassination?
In 1956, the video tape (an analog magnetic tape media) became a commercially-available technology.  However, in terms of quality it would, for some years, remain inferior to the kinescope / telecine method of recording live TV footage. The latter technology - kinescope / telecine - is where motion picture filmstrip is used to record live broadcast footage off a CRT; footage that was originally captured with a tube-based video camera.
Consequently, while video tape recording soon became significantly cheaper (around $300 an hour compared to $4000 for kinescope) - and had all the advantages of instant turnaround (no film-developing) - video tape wasn't immediately nor universally adopted by the television networks for recording live broadcasts.
However, a little later, there was a cross-over of technologies - kinescope and video tape - a period of time when both were in common use. Discerning viewers were presumably familiar with their individual peculiarities.
Though by 1963 - the year of the JFK/LHO assassinations - some seven years after magnetic video tape first came to market - it appears that video tape was not only much cheaper but by then had improved so much in quality that videotape was reportedly "far superior to kines" (kinescope recordings of live TV footage). 
Here, things become curious. Those darkened corners of the frames in the LHO assassination footage imply that at some point in its history, the footage was a motion picture film recording, of some nature. (Darkening of frame corners isn't possible with magnetic video tape recording.)
So it would seem that the Ruby-LHO "assassination" was either:
(i) pre-recorded with motion picture film, and 'on the day', projector-screened and re-captured with a tube-camera and broadcast "live" to the nation, and re-re-captured(!) from the airwaves with either a kinescope or videotape (explaining the darkened corners); or
(ii) pre-recorded with magnetic videotape, broadcast 'on the day', as if it were "live", and re-captured from the airwaves with a kinescope (explaining the darkened corners) - an unnecessary transfer process, which, if done, was presumably to intentionally degrade the quality; or
(iii) the "assassination" scene was acted out live (as many "shows" were in those days. e.g. the British TV soap opera, Coronation Street was apparently broadcast live right up until Feb 1961. Here's a 'Corrie' kinescope recording from Dec 1960 for comparison  ) In (iii) the acting of the LHO assassination would also be captured with a tube-camera, and also genuinely broadcast live, but for posterity, recorded off the airwaves using a kinescope, as that first Corrie episode apparently was. Which also makes little sense. If there were no blunders in the footage, wouldn't the hoaxers want to record their handiwork in the best quality of the day - which by 1963 was afforded by videotape, and not kinescope?
Also, if (ii) or (iii) was the method used, why would the hoaxers use / need the crude celluloid-layering technique that Simon noted earlier?
 http://www.earlytelevision.org/now_they ... _tape.html
 http://books.google.co.uk/books?id=vyoD ... &q&f=false
edit: forgot method (ii)