The fine art of editing videotape

[Spot Wobble]

All professional motion picture filmstock (eg, 16/35mm negative) has film edge numbers exposed at regular lengths on its edges, outside the picture area: these edge numbers become visible when the film is developed, and can be printed onto a 'cutting copy' or work print'. The work print was edited in a film cutting room: when everyone was satisfied with this edit, the original film (negative or sometimes reversal original on 16mm film) was cut and matched to the work print via the edge numbers.

35mm originals (eg, feature films) tended only to have takes selected by the director printed: some takes might be printed in colour to get some idea of the colour balance of the scene, whilst others used to be printed in black-and-white for economy.

For 16mm (eg, film shot for television) whole film rolls tended to be printed (to minimize film handling, and potential damage), often in B&W for economy.

Later on, 'machine readable' film edge numbers were included on the original. As original film (negative) became increasingly edited on video or non-linear computer systems, the 'machine readable' numbers could be read by the telecine machine or film scanner as the pictures were scanned, forming part of the metadata for the editing systems - if necessary, the original film could be cut with reference to the data produced in the edit, although I think the cutting of the original film is now very rare (indeed, shooting on film itself is now much rarer).

[ppppenguin]

The BBC did lot of (monochrome) telercording on to 16mm. I find this hard to believe but ISTR 16mm telerecordings were used into the 1960s, possibly even the 1970s, to make edit decisions. The BBC also did a lot of work on telecine from 16mm colour negative. I don't know why they didn't simply use reversal film when time was critical. Or maybe they did and I've got the wrong end of the stick.

Christopher Nolan is one of the few directors who still shoots on film. A friend of mine was in charge of rushes for Dunkirk which was shot on 65mm 15 perf and Imax. Rushes was the wrong word as the stock had to be flown to the US to be processed. 3 days to get a rush print if you were lucky. Also no video assist so complete trust in the DOP.

[Richard_FM]

Thanks once again for the information.

I heard film reversal was common for filmed news reports, some ITV companies would simply stabilise the negatives & electronically reverse it on playout.

[ppppenguin]

Doing telecine on camera negative isn't trivial. Partly because of the wide dynamic range of negative film, especially when it hasn't been graded for printing. I think that noise and phosphor grain are a problem too with flying spot telecine.

Reversal film is a different thing altogether. Kodachrome and Ektachrome slide film are examples. During processing there is often a 2nd exposure.
https://en.wikipedia.org/wiki/Reversal_film

[Spot Wobble]

Reversal film has limited exposure latitude, ie, it has to be very carefully exposed to yield good results. Negative film has more exposure latitude.

Before the news was broadcast in colour, news film tended to be shot AND edited in the cutting room on B&W negative (16mm): therefore a positive image was only seen on transmission (which was generally live telecine transmission then). There is a wonderful story about a film editor who patently didn't know much about sport: he synched up a commentary about a woman golfer to what he thought was the corresponding negative material. On transmission, the accompanying pictures turned out to be of a Scotsman in a kilt tossing a caber!

I have a 16mm telerecording, with burnt-in timecode in vision, of the second episode of 'A Hitch Hiker's Guide To The Galaxy' (produced in 1981, I think). It would have originally had a separate magnetic soundtrack, which I do not have: however, it carries a combined optical track made at the time of telerecording. This telerecording appears to have been made as an aid to laying sound effects and music, which would been used in a film dubbing theatre to make the 'final mix' sound, also on separate magnetic film (sepmag), just as a production shot on film at the time would have done. In this case, the fully-mixed sepmag sound would have then been 'laid back' to the transmission videotape.

The telerecording has some chinagraph marks on the picture in places (to aid track laying for the sound). The optical track is of the original studio sound only: for instance, there is muffled 'guide sound' only for Marvin The Paranoid Android (presumably voiced by the Android prop operator on the set at the time of recording).

Best wishes,

Francis

[ppppenguin]

Great story about the golf and caber tossing.

Today's TV and film programme makers must have little idea how technically tough it was back then. It still takes a lot of skill to edit well or to mix a good sound track but the technology is usually no longer an obstacle.

[Yellowtriumph]

Great story about the golf and caber tossing.

Today's TV and film programme makers must have little idea how technically tough it was back then. It still takes a  lot of skill to edit well or  to mix a good sound track but the technology is usually no longer an obstacle.

I hope my first post may fill in some blanks.

During the days of physical splices of Quad tape everyone mentions the Smiths tape splicer with its use of Edivue solution to develop the video and control tracks. But it was not the only splicer. A company called EMT which many here will remember for their professional audio equipment also produced a physical Quad tape splicer. In the EMT model's case it was not necessary to 'develop' the video and control tracks, instead it was equipped with a small rotating head that scanned the control track along its axis and produced a display of the resultant waveform on an integral scope. The tape was clamped into position and held there with a vacuum aperture and moved fractionally backwards and forwards whilst observing the trace to view the control track and edit pulses to accurately position the tape linearly in the tape path. At the desired edit point a guillotine was then brought down across the tape to cut it. Otherwise it was similar to the Smiths splicer. The vacuum was derived from some sort of vibrating relay system - it was not any sort of piston or pump and I believe this was a popular technique when only small quantities of 'vacuum' are required.

Not many of the EMT tape splicers seemed to have been sold in the UK. I know of only few examples as the years go by. In fact, I obtained one myself when the company I worked for was downsizing and needed space - it was nearly put in a skip.  After some consideration I donated it to the people who run GoldenAge TV. I'm sure you will have heard of them - I thought the splicer had a better chance of long tern survival with them rather than me. On the earlier link to the BBC Oldboys website you may remember they mention the EMT splicer in passing saying how difficult it was to now source a picture of it - if only they had contacted me!

This general editing technique was reasonably quickly surpassed by edit tone techniques once Ampex and RCA had mastered the electronic sequencing that was required to selectively erase and record on the video and audio tracks. By this method a tone laid down on the edit machine Quad Cue track drove the editor to preview and perform edits as well as rolling ancillary equipment in sync with the master Edit machine. Ampex called their editing kit 'Editec' whilst RCA called theirs 'TEP' (Tape Editing Processor). 

I was going to suggest to 'Spot Wobble' that if he is still playing back tapes from the late 60's through to the mid-80's at the BFI, that it might be interesting to listen to the Quad Cue track on occasion to see if he can hear the audio editing Cue tones, they are very distinctive!

With regards to the quote above - absolutely. In the days of PAL colour for example you had to be on your toes to maintain the PAL subcarrier sequence over the edit point if you needed to (animation editing for example) and editing was as much an engineering function as an artistic one. 

I was once talking to a top flight editor who told me the following: "You can fool the audience about a terrible video edit with a good audio edit - the audio edit will disguise the poor video edit, but you will never disguise a bad audio edit with a great video edit - the ear is much more sensitive to discontinuities than the eye". I never forgot that because, well, its true!

I hope these bits may may be helpful. My personal timeline of tape editing was Cue tone through to timecode, but by then the computers had taken over and it was no fun anymore!

[ppppenguin]

Hello and welcome to GVR.

Thanks for all the additonal information. You mentioned Golden Age TV. One of the partners in GATV is Paul Marshall who I visted today at his home near Lincoln. He and I are also trustees (he's chairman, I'm treasurer) of a new charity: The Broadcast Engineering Conservation Group (BECG) https://becg.org.uk/

The PAL sequence was a tricky beast for VT editing.A related topic is subcarrier to H phase. This must also be reasonably well controlled to eliminate a 4 field ambuguity in the 8 field sequence. I've done a lot of work on this as part of designing SPGs, something I've done for many years for Courtyard Electronics.

[Yellowtriumph]

Many thanks for the welcome. I have met Paul and given him a few obscure bits and pieces over the recent years. I hope he is looking after that editor - I know of only one other in the UK! Very rare.

I'm familiar with some Courtyard kit, in particular the VT Clock in SDI days. Very reliable as I recall. For SPG's we used Acron and subsequently Trilogy Mentor. We would sort of routinely check the Sc/H phase on the outputs of the production studios to ensure they were within spec. We took the easy route and used the a TEK Vectorscope unit that gave the circular loop and 'dot' position to indicate the precise Sc/H phase setting. I think stability was perhaps more important than accuracy.

You may know, but in the very early days of PAL although it was appreciated that line syncs and subcarrier both had to be within their respective +/- specifications, it was not realised that they had to be actually locked to one another. It was discovered, when playing back colour tapes, that due to the electro/mechanical nature of a VT machine that the VT's mono timebase corrector could be gently correcting in one 'time direction' and the colour timebase corrector could be gently correcting in the opposite 'time direction'. Usually the colour time base corrector feeds back into the mono timebase corrector which then feeds back into the head servo to keep it all Hunky Dory. In the example I give above, the CTBC would eventually run out of range and dump uncorrected video into the MTBC which would also run out of range and dump uncorrected video into the head servo causing the picture to twitch sideways! I think this was appreciated in the very early days and from then on line signals were derived from subcarrier so it was all locked. I think you will know much more about that than me.

A final thought, I can't remember if it was an agreed industry standard or not but the Acron SPG's could be User Linked to give a full single line of white video (On a particular line in the vertical interval) to indicate Field 1. Looking at a signal on a monitor you's see the white line flicking at 8 times a second (Obviously). All well and good, but we never used that facility. Until one day ..

.. someone decided to change the Acron SPG on a telecine machine about to play out a live children's cartoon and set that User Link to output this signal for some unknown reason. All was well until the machine was cut live to air in presentation. Then all hell broke loose and after 30 seconds or so it had to be whipped off air. What was not realised was that the Grass Valley Presentation desk used that self same line to perform a vertical clamp on the video, it did so, and caused the resultant video desk output to be jabbering away to nonsense on a regular heartbeat 8 field pattern! Happy days, and then the computers took over.

[ppppenguin]

All the SPGs I have designed have had a user selectable F1L7 flag. It's not quite a standard but it's commonplace. It's not a 100% guarantee that SCH phase is correct. I like the story about the GVG desk using the active part of L7 as a black level reference. Naughty GVG.

If the F1L7 flag isn't present on a signal you can't, in isolation, determine the 8 field sequence. 180 degree SCH error is simply saying that F1 is actually F5 etc. If two sources are genlocked then you can determine whether they are 0 or 4 fields apart.

The VT clock has an interesting history. From 1980 to 1984 I worked for Michael Cox Electronics as a design engineer. Thames TV had designed a largely analogue VT clock which Cox made under licence as model 350. It was a bit of an abortion - I looked at some its problems once. The guys who started Courtyard were colleagues at Cox. One of them designed the digital Cox 650 VTR clock. I wasn't involved with either the Cox 650 or the CY200 clocks but I think the designs had certain similarities The only VT clock related job I did for Courtyard was a little add-on PCB to convert the output to SDI. A bit of a kludge but it worked well enough.

I didn't know the Amtec/Colortec story. Herr Bruch certainly decreed that SC and H were to be locked to each other in PAL and I thought all broadcast grade kit ensured this was so. Though the concept of SCH phase came later. Outside broadcast grade kit "wild" subcarrier was commonplace.