The size of hard drives and amount of RAM available on home PCs today, enable us to do things that early developers would not have dreamed possible. One application of interest to an increasing numbers of PC users is video editing.

If you look around, you will see more and more people using camcorders to record holidays and other events.

When we take photos, we can always throw away the ones that aren't any good. With video we need to edit out our failures. Usually this has been done by dubbing the successful cuts to tape and assembling them in some sort of order. This is basic video editing.

Since camcorders also record sound, successful video editing becomes a multimedia production. It doesn't take a lot of lateral thinking to link multimedia to PCs.

There are two basic PC editing methods in common use, linear and non-linear.

With linear editing the computer controls the "Source" deck (often the camcorder) and the "Record" deck. The better programs have a hardware device that you can use to overlay titles, effects, graphics etc, from the computer during the production of the final tape. The actual footage is copied directly from the master tape(s) to the final tape.

Non-linear editing uses the process of "grabbing" the footage into the computer (encoding), manipulating the data (editing), creating an "AVI" file and then sending the file to a VCR (decoding). This is done with hardware dependant "CODECs" (COde--DECode).

Linear editing

If you intend to do linear editing it would be wise to check any camcorder you are contemplating buying to ensure that it has one of these hardware control options before buying it. (Digital camcorders use "Firewire" links between the camcorder and the computer. Firewire includes device control. Currently non-linear editing is the cheapest viable digital option.) A popular linear PC editing program is Studio 400. It needs "SmartCable" and "Studio Mixer" hardware. The SmartCable connects to a COM port and controls both the source and the eecord devices.

The mixer connects to an LPT port and enables you to mix video signals. The video signal from the source goes via the mixer to the record deck. The LPT connection enables overlays (for example titles, captions, graphic images), still images, and transitions to be applied to the record deck from the computer.

It is also used by the computer to "grab" a low resolution AVI file of the footage for editing purposes. Partnered to this AVI file is the creation of a sequence of "picons" (pixel icons) which represent, graphically, the clips in the AVI file. This enables easy WYSIWYG editing of the footage. You simply grab a picon and drag it with the mouse to place the associated footage where you want it to appear in the finished tape. You can also drag transitions and other effects to the position required.

Similar editing of sound clips and the creation of sound effects, background music etc, can be applied to the audio component of the video. Once you are in "Create Video Mode", the edited clips, titles, sounds, transitions etc, are recorded on tape in a linear fashion. (Each event follows the previous one according to a predetermined edit decision list order.)

The small AVI file created during editing enables the user to check how the final video will look. Sound is controlled by the computer's sound card.

One advantage of most linear systems, including Studio 400, is that you don't have to "open the box" to use the software. In other words, all the hardware connections to the PC are done externally.

Other advantages to linear systems are:

• Relatively inexpensive to set up
• Able to run on most Pentiums with DirectX 5.0 compatible graphics and sound cards (most current PCs).

The small AVI and/or MPEG file created from it can be used in PC multimedia presentations.  

Non-linear editing

The first hardware requirement is a "grabber/outputter" card. This could be an analogue--digital Coder/Decoder for grabbing and outputting VHS and SVHS footage, or a digital "Firewire" control device for transferring digital information between digital camcorders and the PC.

Unless you are working on very small clips you will need lots of hard disk space. You will require 1 GB of hard disk space for every four minutes (digital) or six to eight minutes (SVHS) of completed "full frame" AVI. Allowing for the AVI file clips required to edit as well as the space required for the AVI file itself, you may require as much as 3 GB of HD space for every five minutes of production.

The hard drive must be able to handle continuous data flows of around 6 MB/s. This usually means an AV rated U/W SCSI drive, however Ultra IDE drives, combined with an IDE RAID system seem to work, and offer a cheaper alternative.

The compression at which the footage is encoded has a great deal of bearing on the hardware requirements required. If your needs are modest and you are prepared to accept lesser, yet reasonable quality, a high speed (7200 rpm) IDE drive will suffice.

The minimum PC required would be a P166 MMX with 32 MB RAM. A P2 300+ with 64 MB is a better choice if you are buying with a view to video editing.

With the explosion of interest in PC video editing there are several cards available to do encoding and decoding to and from the computer. Matrox uses a system that places a daughter board on the PCs graphics card. The Rainbow Runner is a reasonably priced option if you already have a Matrox card.

Other lower price units such as Buster and Buz may prove adequate for some users but so far, their performance seems limited to smaller tasks. At the other end of the scale are professional cards costing many thousands of dollars. They are beyond the scope of this article.

I have, so far, had 6 different cards through my computer and have found that the MJPEG CODEC from one brand is unrecognisable by the next brand. Not much benefit had I saved each production other than on the completed video tape.

The term non-linear refers to the fact that, when editing you use clips that can come from anywhere, as long as they are encoded to the same standard. As well, you can reverse a clip, combine several clips at once, speed up or slow down a clip, freeze frames, resize and perform many other "tricks" as required. This can be done in any order and once the AVI file is created, it can then be re-opened and re-edited. (Using linear video editing techniques you would have to go back to the original footage to re-edit the video after completion.)

There can be problems for long term storage of non-linear video editing productions, other than the completed tape, because the files are so large. Perhaps DVD will answer this problem.

There are several consumer-level non-linear editing programs. Foremost are Adobe Premier and U-Lead Media Studio Pro. These can be used with any card. Another good editing program is DPS Video Action Pro which is only usable on Edit Bay.

These programs, together sometimes with plugins, enable home video-editors to produce Hollywood-type productions. In fact most of the glitzy effects you see on the TV are available to the home user.

There is a problem with the AVI format which occurs at the 2 GB mark, where sound and video go a bit berserk. Current versions of editing programs work around this problem by creating several 2 GB files and seamlessly switching from one to the other. This is a workaround until the next version of AVI which is rumoured to be able to handle terabyte file sizes. Sounds like overkill but when AVI was developed it was inconceivable that an AVI file would ever grow to 2 GB.

Having said that, watch future trends. The linear editing process used by Studio 400 is not dissimilar to basic non-linear editing without the glitz. Pinnacle recently released Studio DC10 plus non-linear consumer video editing system, which uses Microsoft's Direct Show technology. With it a user can capture MJPEG video and audio and then either create a new MJPEG file or output to video-tape. Many of you will have already seen this product demonstrated at our February meeting.

There are other developments currently in the area of compression. Some cards offer grabbing using MPEG instead of MJPEG. Also we await the long overdue wavelet compression boards.

Video on the PC

There are several PC cards that are designed to simply "grab" video for use on the computer. They do not have an encoding capability but if you only want PC files they offer a cheap option.

PC AVI files are usually small with low resolution. There are a number of PC CODECs available from Microsoft, Intel Indeo and Cinepac from Radius. Fortunately these CODECs are standard and therefore capable of being played on any PC using Media Player.

Another common PC format is MPEG (Motion Picture Experts Group) These finished videos are for showing on a computer or sending electronically to someone.

Common hardware CODECs use MJPEG (Motion JPEG) compression because every frame is compressed. This means that you can cut to any single frame. MPEG compression works with "Key" frames every so often with each subsequent frame only noting changes from the preceding frame until the next "Key" frame. The usual size of MPEGs for PC is about quarter-screen (352 x 240). If played at full-screen some pixellation is perceptible but it is an acceptable trade-off for a much reduced file size.

Conversion from MJPEG to MPEG is achieved in several ways. The most common is by software compression with programs like Xing encoder. These programs are very slow and typically take 30-60 times the duration of the original file. Power users can obtain a hardware option which does the conversion much faster.

Another method is to actually save the completed video from the editing program as MPEG using plugins such as DVMPEG.

External units such as the Python can convert video tape directly to MPEG for use in a PC. The advantage of this is that 30 minutes of video takes 30 minutes to encode to MPEG, whereas a software converter would only do around one minute of conversion in that time.

Current editing programs such as Media Studio also now enable you to work on MPEG files, but that is another story for another time.