Article: Interformat Editing

Final draft. Rev. D 4729 words

In March's issue of VPM magazine I wrote about our field production experiences in Israel for a Christian group tourism promotional video. May's issue covered the nonlinear "off-line" editing experience for this project and this month I discuss the equipment used for the interformat "on-line" editing.

Our crew shot 43 hours of raw camera stock over 12 days in Israel using the JVC KY-17BU broadcast camera with a Super VHS dockable BR-S411UB recorder and a JVC GY-X1 one piece 3 chip camcorder. We narrowed the best of that footage down to under 3 hours using a standard logging program, and then made most of the editing decisions by cutting and pasting it into shape using an EMC2 nonlinear off-line editing system. From there, I took a standard CMX 3600 edit decision list (EDL) on a floppy and loaded it in the AmiLink/VT edit controller to assemble the on-line finished product.

On the source side I used the new JVC BR-S525U slow motion S-VHS player and the BR-S822U player/recorder. The record side was the Sony PVW-2800 Professional Betacam SP. The switcher used for most of the project was the Newtek Video Toaster 2.0 because it directly interfaces through Arexx commands with the AmiLink/VT edit controller, both of which were hosted by a Commodore Amiga 2000 computer. The Panasonic MX-50 switcher/special effects unit was also used for compressed "picture in picture" effects which the Toaster cannot do in full resolution. For keying Deluxe Paint real time animated map graphics from a second Amiga, I used an Omni-Gen 711 outboard genlock from Omicron Video. To scope all the shots for proper levels, I used a Magni Monitor waveform/vectorscope. For monitors the "amazing" 13" Sony GVM-1311Q monitor and a Sony PVM-1390 were used on the play side as well as a Panasonic BT-M1310Y broadcast monitor on the record side.

You may wonder why I didn't shoot and edit all in one format. The answer is simply that I didn't have a large enough budget to do the whole project in Betacam SP and I knew the S-VHS camera master quality would hold up better if the editing was done to a component (Y, R-Y, B-Y) format. There was a time when interformat editing meant dumping all of your footage to the other format; control protocol and video signal paths have standardized to the point that most professional equipment is now made to hook up to other brands. It has become very practical and affordable to mix and match equipment and formats to suit your needs and budget.

Many video producers are very happy with the quality of first generation S-VHS camera masters when shot with a broadcast camera and using good production values. Editing to S-VHS, is also acceptable for most corporate projects and some budgetary broadcast shows if quality equipment and care is also used in post production. Often, however, the desire is there to preserve the multi-generational quality more than any heterodyne format (S-VHS, 3/4" or Hi-8) can do. Interformat editing from S-VHS to an analog component format (Betacam SP or MII), is a good way to step up in final product quality without making the big plunge to a full component suite. Sony has introduced their PVW Professional (industrial) line of Betacam SP which now makes it affordable for those wishing to gradually trade up in quality. About the only downside of interformat editing between any two different formats, is the lack of ability to take the tape from the recorder and put it in the player.

To account for the differences in quality and price between S-VHS and Betacam SP, one needs to understand several of the specifications. Both formats have a similar luma (luminance, black and white) resolution exceeding 400 lines of horizontal resolution, but the colour (chroma) resolution (bandwidth) is one of the greatest differences. The human eye is not nearly so discerning about colour resolution as it is with luma, so all formats record less chroma resolution. The problem starts to manifest itself once you've gone down several generations and the colour starts to slur or bleed over the edges. Heterodyne formats such as S-VHS, downconvert the 3.58 MHz chroma signal and place it at a lower frequency than the luma and record the combined signal to tape with one pair of heads. The space (bandwidth) available for the chroma is quite limited and therefore, limits the colour resolution. Analog component formats record the chroma signal using a second pair of adjacent heads, thereby allowing for 2-3 times more chroma resolution. The greater amount of tape surface area (real estate) that the video heads come in contact with and the higher packing density of the metal particles on a Betacam SP tape also allow for greater signal to noise (S/N) and less noticeable drop outs. Betacam SP also has a dedicated linear time code track so you don't have to free up one of the two linear audio tracks for time code. Of course, any VTR can use Vertical Interval Time Code (VITC) instead of Linear Time Code (LTC), just as we did in Israel.

Not to be outdone, JVC and Panasonic have made significant improvements to their professional S-VHS editors to ensure that their multigenerational capabilities make them a viable production format. It is inappropriate to compare S-VHS with Betacam SP since they are clearly aimed at different quality levels of the market and are offered at different price points. It is appropriate to use either format or a combination of the two, depending on the budget and quality level requirements.

Since the edit controller is the device that ties it all together and tells each machine what it's supposed to do, I'll discuss this area first. For this project, I was looking for a computer based edit controller that was appropriately priced for the kind of equipment it would be controlling. I used the AmiLink/VT (Video Toaster version) made by RGB in Florida and distributed in Canada by Amiware Inc. of Markham, Ontario. The AmiLink/VT consists of software and a board that resides inside a Commodore Amiga 2000 computer with two of its three V-LAN transmitter/receivers built on the board and the third V-LAN receiver outside the computer. The V-LAN Universal Control Network is licenced by Videomedia and is simply an RS-232 protocol adapter that uses device specific downloadable software drivers allowing control of the VTR's or other devices via the nine pin RS-422 serial connection. AmiLink/VT also offers V-LAN's that will control older parallel decks. The AmiLink/VT program has features you would normally expect to find on edit controllers costing a lot more. Because it is software based, improvements and new features can be implemented quite easily. Edit controllers tend to be the type of device where features evolve as users suggest them. Because of the shear diversity of machines that it must control and the multitude of features it must have, it is quite possible that it can do things that you didn't realize, or just as possible, that it may not do something that you want, because nobody else has indicated a need for that feature. For example, the AmiLink/VT does control the new JVC BR-S525U dynamic tracking (slow motion) VCR once you load an appropriate driver "before" entering the AmiLink/VT program. If you tell the folks at Amiware which VTR's you are using, they will preload the appropriate drivers before your AmiLink/VT is delivered, so that it loads automatically each time the program is booted. I found that I couldn't ripple the list without taking separate concurrent audio and video edits and putting them consecutively. Upon phoning RGB, they immediately couriered a beta test copy designed to solve this problem.

Most AmiLink/VT users create their EDL using the Amilink, but it is also designed to take in standard CMX 3600 EDLs from other editing systems. I found that the AmiLink/VT wanted to see everything in a particular spot or it wouldn't load a CMX 3600 list from the EMC2. The solution was to take out the blank line (cursor return) at the head of the list using any text editor. I may well have been the only one to ever try that combination, but the customer service engineers at RGB now know about it and are likely to provide a fix in the next version of software. Although you can start using the AmiLink/VT almost right away for simple editing, like any complex piece of software, there is quite a learning curve if you want to make it jump through hoops. Apparently, RGB has recently upgraded their manual to reflect all of the new software changes that have taken place.

I particularly liked the AmiLink/VT's ability to directly control the Toaster effects, including the timing of the character generation (CG). Options are available to control other switchers via RS-422 or general purpose interface (GPI) triggers. Much of my frustration had nothing to do with the AmiLink/VT, but rather, the limitations of the Toaster 2.0. One usually uses a transition (wipe, dissolve or effect) when changing locations or themes and often immediately followed by CG. The Toaster 2.0 and the Toaster 4000 soon to be released, cannot do a one pass transition immediately followed by CG (alpha keyed). Since I was using SMPTE time code for frame accuracy, the solution was quite easy. AmiLink/VT has a "Copy and Append" feature which automatically makes a spare copy of the edit being worked on and puts it at the end of the list. I simply trimmed the "in" points of the spare copy to occur after the transition, turned the edit from a "wipe" into a "cut" and laid the shot back in with CG this time. The AmiLink/VT not only allows the duration to be set for CG, but also allows the "in" point of the CG to be set via the GPI1 to a different point than the video. It can even be programmed with a negative number so the CG is already faded in when the video "in" point is reached. This repeatability of timing for CG was a real treat, since I have been accustomed to manually activating CG.

When using the Toaster in a time coded frame accurate A/B roll, it is very important to note whether you have selected a "digital" transition or an "analog" transition. Digital transitions turn the analog video to digital and delay it for two whole frames using both buffers to process the video, then back to analog again. This two frame delay can cause a jump in your picture if the join point of an A/B roll has analog processed video on one side and delayed digital processed video on the other side. The solution, is to pick an analog transition, or trim the in point of the "from source" back two frames.

Analog transitions are variations on wipe patterns that do not affect the size or position of the video and are characterized by a light blue computer screen during the transition. Digital transitions turn the computer screen dark blue and usually affect the picture in a geometric way. Because a digital transition goes through so much conversion, there is also a hue change that takes place when activating a digital effect. The two frame video delay of digital effects, throws the video subtly out of lip sync with the audio. If your timebase correctors or other devices were also delaying the video or you were working with second generation footage, the lip sync on a talking head could be disturbing. The solution, is to enter a talking head scene with an analog move or purchase a digital audio delay and turn it on whenever you are in digital video mode. Alternatively, the audio could be offset by the appropriate amount and laid in as a separate edit. Since digital effects need this delay to process the video, it would be nice if the Toaster delayed all video and had a built in stereo audio delay to match.

The Commodore Amiga 2000 which I was using, was equipped with a 68030 accelerator, but only 6 Meg of fast ram and 1 Meg of chip ram. This amount of memory is the bare minimum required for running the Toaster switcher, CG, AmiLink/VT and large EDL file. Toaster paint was not accessible because of a memory shortage. I would recommend that purchasers equip their systems with at least 8 or 9 Meg of fast ram and another 1 Meg of chip ram, depending on which programs are usually running. With all the processing going on, the ram memory can occasionally get fragmented. If there isn't enough contiguous memory, some of the Toaster's effects will show artifacts that look like luma keying in spots. The solution, is to save the work files that are open, and to cold boot the computer. The AmiLink/VT allows for the standard slow, medium and fast speeds over the Toaster effects, as well as custom speeds. Unfortunately, many of the Toaster 2.0 effects will only work at predetermined speeds. If the custom speed you choose doesn't work with a particular effect, revert to one of the standard speeds.

Although I used the Toaster's character generation program, I loaded it with fonts from Shereff Systems Inc.. For the opening title I used a "Cinnamon" font called "Hammered" which is a 24 bit 3D type font and has a thin black outline around it so that it contrasts with any background. For all the regular titling I used a very legible, more standard font called "Modern" from their "Bread & Butter" package. Shereff fonts come with wider and more pleasing spacing (kerning) than Newtek fonts, though both are adjustable.

Contrary to popular notion, signals across a hard wired composite line don't have a resolution limitation. A broadcast composite signal does have a hard limitation of about 332 lines of horizontal resolution because only about 4.2 MHz of a TV channel is reserved for the picture. Each 1 MHz of bandwidth roughly translates into 80 lines of horizontal resolution. Even though the Toaster works with a composite signal, it has more than enough transparency (over 500 lines) to be used as a post production switcher and can accommodate any professional tape format. The Toaster does not meet the higher resolution of broadcast cameras and will, therefore, soften the image slightly if used as a live field production switcher, but that is not its main market. Losses on a composite signal depend on the quality of the encoder/decoder. If a TBC or VCR are using an inexpensive decoder on the composite "in" signal, it will waste some of the luma information (resolution) trying to separate it from the chroma. The real problem with composite is the chroma dot crawl along the edges of highly colour saturated objects. The Toaster does not need to separate an incoming video signal into its components and is not responsible for introducing dot crawl on the original video. However, the Toaster does encode character generation (CG) and alpha keys it over the video, and that is a source of dot crawl. If the CG saturation level of the colour is kept low (light yellow), the dot crawl will be minimized.

The Toaster is not capable of running as an Amiga graphics (alpha key) genlock at the same time as the switcher is running, but still-frame IFF files can be loaded through the paint program and luma keyed over video with the switcher running. Since I was using an animated Amiga graphics map of Israel using Deluxe Paint IV, I had two choices. I could quit the Toaster program and use the Toaster as a stand alone (alpha key) composite genlock with the usual dot crawl on highly saturated chroma edges, if I didn't need the CG or switcher functions. Instead, I used a second Amiga 3000 to generate Amiga graphics and alpha keyed them over the video using an Omni-Gen 711 genlock. I fed the composite signal from the Toaster to the Omni-Gen 711 which has the ability to transcode video, cleanly to Y/C, then the Y/C signal was taken from the Omni-Gen to the PVW-2800 Sony Betacam SP recorder. This method eliminated any dot crawl on the Amiga graphics. The animated map graphics were created by Image Group of London, Ontario and they have really impressive viewers.

A Genlock is a Red/Green/Blue (RGB) to video "encoder" which "genlocks" (locks or synchronizes) to the incoming video signal and "keys" the native graphics and colour palette capabilities of a particular computer platform over the video. When a Genlock, (like the Magni "VGA Producer Pro") is designed for an IBM computer, it also has "scan line conversion" built in, to turn the graphics from progressive scanning to interlace. The Omni-Gen 711 is an outboard Genlock with its own power supply and can therefore, hook up to any Amiga. The Omni-Gen is one of the most expensive genlocks for the Amiga but it really is a Cadillac unit which has helped to bring some respectability to the Amiga computer for video. The Omni-Gen has a total fade to black control for Amiga graphics and incoming video, so it can assist the proc amp controls of a TBC by letting you compress a hot signal down to legal levels. As a native Amiga graphics (alpha key) genlock, in a side by side comparison with a Toaster, the Omni-Gen 711 wins hands down.

One of the new gems in JVC's S-VHS product line is the BR-S525U player. This is a variable (dynamic) tracking player, that can play video back at a variety of speeds, without any noise bars, in a forward or reverse direction. Initially, a video producer might assume that this has limited application. After working with it for awhile, I started to realize that the BR-S525U has far greater practical advantages than just the soothing slow motion effect. When doing a long zoom-in on a subject, a cameraperson often does several takes before the subject material is in the right position at the end of the zoom. If you start the shot already zoomed in and do a pull out, the shot can be reversed in post production, making it possible to get the right shot in a much shorter period of time, or to salvage shots that would have been useless. Of course, you must make sure that the subject material is suitable for playing backwards or your "trade secret" is blown. It looks really odd to see traffic or people going backwards. Camera footage that is too long or short to fit a given spot can now be made to fit like a glove, thanks to the new JVC variable speed player. Footage that was somewhat bumpy, such as our aerial coverage of Israel, can be played at a slower speed, which gives the appearance of a much steadier shot. Conversely, playing footage at a faster speed can make it appear to be less smooth and a bit (juddery) like a two-field standards converter if there is a lot of movement in the shot. If there is a shortage of footage or your client really likes a particular shot, it can be used in reverse the second time so that it doesn't appear like repeat footage. The JVC BR-S525U variable speed ability, moves the S-VHS production format to a new level of professionalism. I fully expect to see a lot of Betacam and 1" editing houses, add a full featured JVC BR-S525U to their equipment list so they can attract new cliental who are shooting on S-VHS.

The BR-S525U comes with a built-in (TBC) as a functional part of it's variable speed capabilities. The TBC worked well and had plenty of range using the proc amp controls. The BR-S525U has composite, Y/C and component output connections. An optional digital chroma/luma noise reducer (DNR) is available. Based on the impressive results that I saw at the NAB convention, I would recommend purchasing the CNR with the BR-S525U. A time code card is also an option which is essential for A/B roll editing and extremely handy for identifying footage. I also used the JVC BR-S822U which can operate as a source or record-side editing VCR. A TBC is optional on this model, as it is not needed if it is only used on the record side. These two units would be all that many video producers would need to set up a high quality "cuts" editing suite. These units will accept, without an adapter, either full size or "C" size cassettes.

On the record side I used a the Sony PVW-2800 Betacam SP recorder/player. It was a joy to work with a unit that was so reliable. I never once detected a noticeable dropout despite some pretty heavy duty shuttling and editing. We had a 24 bit, 30 second animation created for the opening scene by Dave Jerrard of Bluestar International Inc. of London, Ontario. He used the Lightwave program in the Newtek Toaster 2.0 to create the animation and recorded it a frame at a time to the Sony PVW-2800. Single frame animation recording is very hard on a VCR and the tape. Never the less, the PVW-2800 Betacam SP did the job perfectly. The artistry of an animator is a talent in its own right. I wouldn't think of taking the time to learn a complex animation program when there are talented artists like Dave, to create such high quality animations. The animation starts by looking at earth from outer space and zooms in toward North America, then starts to orbit around until the viewer arrives at Israel. Some of the background music also came from Gary Sykes, of Bluestar.

The PVW-2800 is one of Sony's new, industrial priced, Betacam SP products. The line is considerably less expensive than their BVW broadcast series, with only a few features eliminated, such as HI-FI audio. I have learned how to take advantage of the HI-FI tracks of S-VHS to give myself an extra channel of wild sound, so I miss that feature. HI-FI audio can be inserted on the linear audio tracks of the same tape without going down two more generations and without going out of lip sync. The PVW-2800 can not record on regular oxide tape. It uses the metal tape to optimize picture quality. It will play back regular oxide tape and accommodate either size cassette with the larger cassette running to a maximum of 90 minutes. It was especially nice to see the purity of the second generation chroma and to observe that it wasn't banding. The PVW-2800 has composite, Y/C and component input and output connections. A TBC is built into most Betacams as it is an important part of the chroma play back circuitry. The TBC can't be turned off in this model, so you must ensure that it is at unity gain when being used as a recorder, so that accurate scope readings can be taken at the output. The PVW-2800 supplies reference sync for itself and the rest of the components in the system. I looped through the reference sync from machine to machine, but a more reliable way would have been to use a distribution amplifier such as the new industrial priced Mix Box series from Leitch (Hedco).

It is a good idea to take scope readings before and after the signal leaves the recorder. I found that "source" black level (setup or pedestal) wasn't affected as much at the EE (Electronic to Electronic loop through) output of the PVW-2800 as it was at the input. Obviously the PVW-2800 was trying to counteract my pedestal adjustments. I used a Magni "Monitor" waveform and vectorscope from Applied Electronics. This inexpensive unit dispenses with the conventional expensive calibrated green CRT screen and uses any monitor with a video input as its display screen. The graticule is superimposed on the screen for accuracy. The Magni monitor has 3 separate composite inputs with loop-through, or all 3 can be used for one component channel. The new Magni Monitor 400 will also accept 2 Y/C loop-through inputs. Because this scope has a reference input, it can be used to time-up a system. Unlike some of the inexpensive scopes on the market, this one met all of my basic needs. Even though I use my trustworthy Panasonic BT-M1310Y broadcast monitor on the output of the recorder, I find it absolutely essential to scope each and every shot, so I know exactly what the recorder is seeing. I don't know how some video producers do without a waveform and vectorscope. Reading a scope is really quite simple and not the engineering mystery that people think it is.

A broadcast monitor such as the Panasonic BT-M1310Y is designed to show up problems while you can still do something about it. Unlike a display monitor which is designed to mask problems and typically make skin colours look right, the phosphors of a broadcast monitor will show the most subtle changes in skin colour. Features such as underscan allow you to see the entire raster if desired and crosspulse shows the horizontal and vertical blanking so abnormalities can be checked for. Bluegun helps to calibrate the colour hue of the monitor to bars and provides a way to check the noise levels of the chroma signal. Every decent editing suite should have at least one broadcast monitor, usually on the recorder output.

Recently, I purchased a Sony GVM-1311Q graphics monitor. This monitor seemed a bit expensive at first until I realized how versatile it was. It is a multisync monitor that can hook up to nearly any computer output, analog or digital, progressively scanned or interlaced. It will also accept a composite or Y/C input in NTSC, PAL or SECAM. The resolution is exceptionally high and it apparently is very low in radiation exposure, for those who worry about sitting in front of a tube all day. The only thing I don't like about it is the tiny little audio speaker.

For a brief part of the editing of this project, I used the Panasonic AG-7650 and AG-7750 S-VHS machines on the source side. They come with built in TBCs and performed very well, especially in the area of chroma noise. Factory installed TBCs are often a better match for a VCR than outboard TBCs. One of my camera master tapes used the 18th and 20th lines of the vertical interval to record time code (VITC). The Panasonics only read and write up to the 19th line so reading the time code was a problem. In future, I will use more standard lines like the 16th and 18th lines for recording VITC.

I also used the Panasonic MX-50 digital switcher for a brief while. This unit allows for full 24 bitmapped compressed motion pictures, so you can do an over the shoulder "picture in picture" effect. Although I didn't get a chance to explore all the features that the MX-50 has to offer, I was very impressed with the "RGB colour balance" control (which is more than just a tint control). It actually allowed me to correct an important shot that was taken without proper white balance. Tint (hue or phase) is a rotational vector adjustment that does not correct for white balance problems. The new MX-30 from Panasonic, is similar to the MX-50 but with less features at a lower price. This item was covered in the Leading Edge Technology section of VPM last month.

Sound effects are often necessary to enhance the video. In this case I needed the engine noise of a 747 taking off to support a sponsor shot for EL AL Airline. I used the compact disc sound effects library from Sound Ideas in Richmond Hill, Ontario.

The widespread use of RS-422 protocol and common signal paths, have bridged the gap between both, formats and, equipment brands. True interformat editing has become a reality, affording the producer or editor the opportunity to select machinery from different manufacturers depending on features offered, or desired.

Les Nirenberg of Nirenberg Communications in Toronto says, "It's a joy to be able to interformat edit from S-VHS to Betacam SP without experiencing an appreciable loss".

Doug Hembruff

Magni MM-400 picture description.

The Magni MM-400 waveform vectorscope, is ideal for cost-conscious producers, offering a simple, accurate gauge to set camera levels before a shoot, or to check timebase correctors and colour fidelity in editing.

Troubles like hue shift, illegal levels, incorrect contrast and clipping of black or white detail, can be easily identified.

The MM-400 converts waveform or vector display information into a standard video signal which can then be displayed on a picture monitor. With its built in SC/H phase and colour indicators, the operator can tell if a signal's subcarrier-to-horizontal phase is properly adjusted.

Picture for MX-50 Panasonic mixer Among the many features of the Panasonic MX-50 AV switcher with digital effects is a RGB colour balance control which allows for correcting improperly white balanced shots.

For more info contact Doug Hembruff.