More and more these days, consumer videomakers are doing more than just shooting footage–they’re
editing. But when it comes time to purchase the gear to do this, they find themselves in a bewildering maze
of acronyms and hyphens: LANC, Control-M, RS-422, VISCA.
“What’s an editing protocol?” you ask the dealer, and they proceed to do what sales people do best: they
try to sell you the stuff that’ll give them the best commission.
If editing protocols confuse you, you’re not alone. Plenty of people get frustrated with the numerous
(and often brand-specific) protocols on the market today. To learn what protocols are and how they work,
read on; we’ll have you out of the maze in no time.
What is a Protocol?
When separate pieces of editing gear talk to one another, the language they use to transmit data is an
edit protocol. A protocol describes how control data moves between machines. When you say “edit control
protocol,” you’re really talking about the data transmission method, not the data itself or the cable that
connects the machines.
For example, if your edit controller is to perform a list of edits for you, it needs some way to tell the
video source to find the right shots, some way to tell both the source and record decks to start playing at the
same time, some way to tell them when to stop and begin the next edit, etc.
Data transmission can be either a one-way affair, or bi-directional. And it can be serial or parallel.
A good example of one-way control is an infrared remote. You can play, pause and even reverse shuttle
a VCR or camcorder with it, but the remote gets no feedback from the tape machine. The remote beams its
commands to the VCR even if the deck’s power is off.
Bi-directional data sharing is easier to do with wires than with an IR signal. It takes at least two wires to
send data bi-directionally–one for each direction of travel.
Parallel data transfer uses a separate wire for each function, while serial protocol uses a time-share
technique: data moves in a continuous stream, one function after another.
Before we get into our discussion of editors, it’s important to know this point: no matter what you use to
control your tape machine, the editing features of a given camcorder or VCR will set limits on your
choices. Just because a certain deck can connect to a high-end edit controller doesn’t mean it can share all
of its high-end features.
Crash and Synchro
A lot of home camcorders and VCRs have flying erase heads and a pause control. This means you can
line up your edits by hand: put each machine into pause, and when you release the pause buttons, your edit
begins.
This technique often goes by the name of “crash editing,” perhaps because you cannot predict the exact
edit point–it falls where it may. Your edit may occur early or late, by a frame or two or 20 or 30.
(Remember, one second of video equals 30 frames.)
The next step up from crash editing is “synchro edit.” In this method, you connect two tape machines
with a remote pause cable. Then, when you release the pause on one machine, the other machine’s pause
also releases at exactly the same time.
The accuracy achieved this way can be somewhat better than the crash method. It usually takes two
decks of identical design. This is due to variations in preroll time, pause release time, and other factors
found in two decks of different makes or models. (The preroll feature makes sure the source machine is
running at full speed when the edit happens–otherwise, you can see a “glitch” or a “hit,” one or two frames
of unstable video, as the edit goes by.)
Even though most VCR makers use a 2.5mm or 3.5mm remote pause plug, the protocol–in this
case, the voltage and polarity–may vary. Panasonic, for example, warns that their industrial synchro-edit
jacks may not work with their consumer gear.
Many Sony consumer products come complete with a jack labeled Control-S. This is their version of
synchro edit–a mini-plug that sends transport commands in one direction.
Preroll Control
Some VCRs, such as JVC’s low-end industrial model BRS-378U, offer you cleaner and more precise edits
with a built-in synchro edit-style protocol that incorporates a preroll function for both decks. You just
connect the decks together via their rear-panel Edit-In and Edit-Out jacks, and you’re ready to edit.
You begin your edit by locating your edit points and placing the machines in pause. Then pressing the
deck’s “preroll” button starts the sequence: the source deck back-spaces five seconds, then rolls forward in
play. Just about two seconds before the edit point, the record deck comes out of pause and prerolls before
the edit takes place.
For truly fine editing, you need tape transports that shuttle, fast and slow, in both directions. Along with
their precise, frame-by-frame search, you’ll want separate audio and video insert edit modes. The following
control protocols will allow you to do all of this and more, provided your decks have these features, and
the proper edit protocol connections.
Control-L
Control-L, or LANC (for Local Application Network Control), is a bi-directional, serial data stream. It
exists on Sony 8mm format camcorders in the form of a 2.5mm connector, and has been adopted by
several other brands.
Many older Sony decks have a five-pin connector but still use the Control-L protocol. These include
VHS, S-VHS, BETA and ED-BETA recorders.
If your camcorder includes Rewritable Consumer Time Code (RCTC), this data also moves down the
wire. Edit accuracy of +/- three frames is common with this system.
Hi8 camcorders and many 8mm units use Sony’s Control-L edit protocol. Sony’s Hi8 edit decks, such as
the EV-S7000, also use Control-L.
Control-M
Panasonic’s low-end industrial camcorders and editing decks use a 5-pin connector and a bi-directional
serial protocol known as Control-M. It is often also called “Panasonic Five-Pin” and is different from
Sony’s 5-pin (even though the connectors look similar).
The control-M protocol has evolved over the years, so you can’t really call it a standard. When selecting
an edit controller, make sure you know what model you need it to work with. On some machines, the
connector is there but the deck may not have some of the editing functions added in later versions of the
protocol.
A popular piece of equipment that uses this protocol is Panasonic’s AG-1970 S-VHS edit deck. You can
use a Control-M cable to connect this deck to Panasonic’s compact edit controller, the AG-A96. The AG-
A96 will also operate the AG-1960, but not the AG-1950, even though this latter deck has the same 5-pin
connector. In return, the AG-A95 editor will control the AG-1950 and AG-1960, but not the AG-1970.
Several Panasonic camcorders have Control-M connectors, such as the AG-3, AG-455 and AG-460.
These, too, will work with the AG-A96 controller. But like most camcorders, they don’t have smooth and
precise jog-shuttle modes. Compared to a real editing deck, it’ll take you longer to find your edit points on
a camcorder. Fast shuttle modes (and even regular rewind/fast-forward) are often slower than the average
VCR; smooth, slow shuttle modes often don’t exist.
How accurate is Control-M? Since there is no time code information sent down the control wire, edits
can be early or late by as much as 11 frames. You can obtain greater accuracy by using time code and a
third-party edit controller (more on this later).
You may have noticed that no current consumer VHS/S-VHS camcorders or editing decks come with
Control-M connectors. In the US, Panasonic, currently reserves editing control for their pro lines. In Japan
and Europe, things are different (see the “Overseas Connection” sidebar).
VISCA
Imagine a video deck that acts like a computer peripheral. Sony builds just such a device–a Hi8 editing
deck known as the Vdeck, model CVD-1000. You can control this machine with your personal computer
via Sony’s proprietary protocol, VISCA.
VISCA appears to be similar to the RS-232 serial interface which most personal computers use to
connect modems and printers. But Sony’s application opens up a number features not normally found on
editing decks with RS-232, such as time and date stamping, a built-in audio/video switcher, fader and audio
mixer, all controlled from the computer.
RS-232
This is the transmission standard for the world of computers. We call it an edit control protocol, but really
it’s just a data transmission standard that has many applications outside the world of video editing.
Computers use RS-232 for communicating with serial devices, primarily modems and mice.
Professional video recorders often use RS-232 cables, which may have either a nine-pin or 25-pin
connector. The advantage of the RS-232 interface is simple: you can adapt it to a wide range of equipment,
including tape decks, edit controllers, effects switchers, character generators, computers and even laser
video players.
Generally speaking, you won’t find the RS-232 protocol on consumer equipment. But you’ll find it as an
option on high-end industrial gear, such as the JVC BRS-500 and BRS-800 Edit Desk S-VHS package,
Sony’s EVO-9650 and EVO-9720 Hi8 editors, and Panasonic’s AG-MD830, a special S-VHS deck
designed for medical use.
RS-422
This is a newer serial interface standard for computers. Most professional VCR makers have adopted it.
Formats such as Panasonic’s M-II and Sony’s Betacam series, both top-quality broadcast decks, use RS-422
exclusively.
RS-422 also goes by the name of professional “nine-pin” serial control. It exists on many S-VHS
industrial machines–Panasonic’s AG-7650, JVC’s BS-S622, Sony’s SVO-9600 and Sanyo’s GVR-S955 are
a few examples.
Even though they all fit under the category RS-422, the protocols vary for each VCR maker. In other
words, they are machine-specific. Subtle differences require changes in the edit controller if you are to use
RS-422 with a given deck.
Choose Wisely
When it comes time to choose an editing system, ask the right questions before you buy. Make sure the
decks you want will work the editor you’re looking at. If you still have trouble keeping all the protocols
straight (as many of us do), take this article into the store with you when you’re ready to make a
purchase.
And be prepared for the upgrade syndrome: within a few years, there’s bound to be some new computer-
based protocols on the market. It’s the nature of technology to be forever changing.
Glenn Calderone is a video engineer, producer and writer.
SIDEBAR
The European Connection
It’s not clear why recent consumer VHS and S-VHS decks sold in the US don’t have Control-L or
Control-M connectors. But similar gear sold in Japan and Europe does have this feature.
Some have suggested that customers in Europe and Japan are more likely to edit their tapes, which
makes them more eager to purchase high-end hardware. But it’s also likely that U.S. marketing moguls
don’t want to offend industrial users by offering too many editing features on consumer gear.
This seems odd when one considers that if control protocols and better sound editing capabilities were
added to high-end consumer VCRs sold in America, the sales of these decks could only get better. And
isn’t sales the manufacturer’s main concern?
As it is, the industry coined the word “prosumer” to describe the overlap, where budget-minded pros use
high-end consumer gear to get the job done.
—G.C.
SIDEBAR
History of Protocols
In the early days of videocassette editing, Sony, with its Betamax and U-Matic formats, utilized a 20-
pin parallel connector for its remote controls, as well as the RM-430 editing controller. This provided a
separate wire for record, fast forward, rewind, etc., plus a wire for the digital counter.
When more features (such as bi-directional shuttle) came along, they expanded the edit protocol to use a
33-pin connector.
Panasonic and JVC each came up with their own style of parallel control. Panasonic settled on a 34-pin
connector, while JVC opted for a larger, 45-pin cable. These early edit controllers were proprietary and
model-specific.
When third-party edit boxes appeared, you had to outfit each one with an interface cable to match each
tape deck.
Serial interfaces appeared first in computers; only later were they adapted to video editing. Serial data
streams require as few as two wires, and you can update them to work with newer machines via software
changes, rather than redesigning the wires and connectors.
—G.C.
