Edit Points: Picking a Protocol

by Mike Loehr
August 1995

If you've spent any time looking at editing systems, you may have come across terms like serial data transfer, Control-L, Control-M and ViSCA. They sound more like things you'd expect from an episode of Star Trek than features of editing systems.

What are these cryptic terms, you ask? They're names of edit control protocols. Generally speaking, protocols are the "languages" that machines use to talk to each other.

Computers use them all the time in their daily exchange with printers, CD-ROM drives and networks like the Internet. In the last decade or so, they have also become something of a standard in videotape editing systems. They let VCRs, edit controllers and switchers talk with each other to improve the accuracy and efficiency of the editing process.

And just as human languages vary, so do electronic ones. That explains why you may see more than one name or type of protocol during your hunt for a new edit deck or edit controller.

If you want to buy a new editing system or just make your current editing setup work better for you, let the next few pages get you up to speed on protocols.

Why Me?
Why do you as a video editor need to worry about protocols? First, it's tough to edit tape efficiently without them. If you've ever spent time editing without an edit controller, you know the hassles of pausing and shuttling machines to get the edit to happen at the right time. Using VCRs and a controller that support some type of edit control protocol will improve the precision of those edits, and cut the amount of time you spend making them.

Second, some protocols work better than others. That doesn't mean you need the best one. One may speed your editing, but leave you broke at the same time. Another may not give you the most features, but might fit better within your budget.

Knowing something about protocols can help you get the one that will do your projects and your wallet the most good.

What is a Protocol?
Despite their confusing names, edit control protocols are pretty simple creatures. They all do basically the same thing: they transfer data and commands between VCRs, switchers, titlers and edit controllers to make editing easier.

Because many VCRs and camcorders can exchange data about the editing process, they can automate those parts of the process that get tedious for us humans.

For example, prerolling tapes prior to an edit and triggering the insert edit mode are two functions that some edit protocols can do better than our fingers can.

Although they serve the same purpose, all protocols don't work the same way.

What makes one protocol different from another? For starters, the simplest protocol gives a one-way link between a controller and a VCR, while more advanced protocols give you a two-way link.

A one-way link is the simplest way to control a VCR or camcorder. Often, a one-way protocol offers a way to emulate what happens when you press a button at the camcorder or VCR. For example, an edit controller might use a one-way link to tell a source VCR to release its pause button and start rolling.

One-way protocols give you a way to trigger very basic editing functions, and can reduce some of the hassles of editing with camcorders and VCRs.

They do have some drawbacks. Because the link between the machines travels only one way, the machine sending the command has no way of knowing if the receiving machine carried out the proper action.

In a simple edit, for example, the VCR that receives the "release pause" command may start the tape too slowly, or the tape itself may have been cued to the wrong scene. Because of the one-way protocol, the controller doesn't know either of these problems exist.

One-way protocols don't work well in situations where you need a high degree of editing accuracy. But they do offer enough control to complete a number of simple video projects.

Two-way protocols make better use of the link between machines. A two-way link allows each machine to keep an eye on when and how the other machines react to commands. This means edits happen more predictably and accurately.

Which direction the data travels isn't the only difference between protocols. Whether the data travels in parallel "chunks" or a serial data stream is another important difference.

Older protocols may use parallel data transfer, where most newer ones use serial transfer. Both work equally well, but parallel systems, while still in wide use, are slowly becoming more obscure. They will probably become harder to find as the years pass.

Common Edit Protocols
Better protocols offer more advanced control of VCRs and camcorders, and hence more control over the editing process. As you might expect, the better protocols often come on decks that cost more money.

Luckily, some newer models come equipped with protocols almost as robust and flexible as their expensive siblings. You'll probably find these the most compatible with your gear and your budget.

Here's a quick overview of all the different protocols and how they rank against each other.

• RS-422: RS-422 is a two-way serial connection using one of the best protocols around, but it's found only on high-end gear. It's found on a wide variety of professional edit controllers, video switchers and decks. RS-422 cables have 9-pin connectors on each end.

• RS-232: This protocol is found on many recent high-end models from Sanyo, JVC and Panasonic. It's a common computer cable connection that uses a protocol now updated to allow control of video machines. With this cable connection and the proper software, your computer becomes the edit controller. Cables look like standard computer RS-232 cables, with either 9-pin or 25-pin connectors on each end. (Remember that both RS-422 and RS-232 refer to the standardized cable connections and not the edit protocol that uses them).

• ViSCA (Video System Control Architecture): A newcomer to the computer-based control market, ViSCA appears on the Sony V-deck series. It works much like the RS-232 protocol, except it uses a special cable provided by Sony instead of a standard computer cable.

• Control-L or LANC: Found on many 8mm and Hi8 machines, control-L is a two-way serial protocol. It permits full control between edit controllers and VCRs. Cables with small connectors, usually 2.5mm or 3.5mm phone plugs, link machines together. Earlier versions used a 5-pin DIN-style connector.

• Control-M: Also a bi-directional serial protocol, control-M appears in most Panasonic pro gear and a few early consumer models. Current consumer gear doesn't have control-M. It uses cables with 5-pin DIN-like connectors and is sometimes called Panasonic five-pin.

• Control-S: Popular on older Sony gear, control-S offers only one-way control between decks, so accuracy is limited. It uses cables with small phone plugs on each end.

• IR: The IR protocol gets its name from the type of connection it uses: infrared. Also only a one- way system, IR works with most camcorders and VCRs that use remotes. It simply mimics the way a remote control operates the machine. But because it's not physically connected, and only uses one-way transmission, IR is the least accurate of the protocols.

• Synchro-edit: A one-way protocol with very limited control, but better than IR. Slightly more accurate than IR, synchro-edit (sometimes just called edit) links the pause buttons of two machines together. When you press a button on one machine, it triggers the button on the other. Found mainly on older camcorders and VCRs.

Are They Compatible?
If we could design the ideal editing system, we'd either make all protocols work with each other or pick the best one and use it on every model.

For some reason, manufacturers don't see it that way. Over the years, they've changed the edit control protocols and connectors found on their various products. As a result, we may have a three-year-old camcorder that uses Control-S, a newer edit deck that uses Control-M and another VCR that doesn't have any edit protocol, just an IR remote receptor.

Your setup may vary, but the overall problem is the same. You need a way to make machines with different protocols work together.

Although some of the protocols share similar-looking cable jacks or plugs, none of them work together directly. In other words, you can't plug an RS-232 deck into an RS-422 controller, or a Control-L cable into a Control-S jack and make it work.

How to make these machines work together? Use an edit controller that supports all of them. But keep in mind that the accuracy of your system will only be as good as the least accurate protocol you use. If a VCR or camcorder in your system uses Control-S or IR, the edit controller won't perform at its best.

Computer-based Editing
Over a decade ago, video editing pros began moving away from stand-alone edit controllers and toward computer-based editing systems.

Computer-based protocols offer a high level of control over VCRs, switchers, titlers and other video gear. They're also easier to update as technology improves.

Gradually, this technology has trickled down into protocols you can use on your own desktop PC, in the form of RS-232 and ViSCA.

If you already own a personal computer, a software-based edit controller may provide an excellent, cost- effective way to edit your videos.

Your Best Choice
So when the dust settles, you probably want to know which protocol is the best for you. That depends on what gear you already have, what kinds of projects you want or need to produce and how much money you've got to spend.

If you're starting from scratch with an edit system, getting one that supports RS-422 protocols will give you the most control. But machines that support RS-422 don't come cheap.

RS-422 decks cost anywhere between $5,000 and $10,000 depending on tape format, and controllers cost from $700 to $3,000 or more.

If that's out of your league, a computer-based controller or stand-alone system based on Control-M or Control-L will perform well. These protocols offer the most control within the current prosumer market.

If you just need a way to cut scenes together more quickly than doing it by hand, one-way protocols may be enough for you.

For those of you who already have a camcorder, edit deck and some other VCRs around the house, you need to shop for a good controller that can link the various protocols together to perform an edit.

A word of caution about these controllers: some products may report that they can perform edits accurate to within two or three frames of a selected point. To get that close to the edit point, they may have used some form of time code on both the record and source tapes, as well as time-code capable VCRs.

If you use the controller with machines and tapes that either don't support time code or use a one-way protocol, don't expect the precision to be that high.

Protocols like Control-S or IR just can't provide the accuracy you get from a time code system. For that reason, you should expect some frame "slippage" when using non-time coded source decks and tapes.

If you've got a personal computer, check out software editing packages for your particular machine. You'll probably have to buy some extra hardware to connect your VCRs to the computer, but this will make it easy to upgrade your system with other desktop video products in the future.

The bottom line is to get a protocol that can grow with you. Chances are good that you'll be wanting to try more and more creative ideas as your editing improves.

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