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Non-Linear
Editing #1 There's a revolution taking place in film-making. Chances are that the last film you watched down at your local multiplex wasn't edited on film. Hollywood is saying goodbye to edit suites cluttered with strips of film and ageing Steenbecks and hello to digital technology. Yes, the movie was still shot on film (for the time being!) but it is was probably digitized to a non-linear computer suite and edited on computer. And this revolution isn't just affecting those people with the biggest budgets - its going to have its biggest effect on low-budget/no-budget film-makers who can now edit films on their humble home computer to a standard that a few years ago would have required a roomful of techie black boxes. Every day the technology gets better and more affordable, putting powerful and professional editing within your grasp. You can now have frame accurate editing, powerful visual effects, sound mixing, titling, blue-screening and CGI modelling all on your desktop. The key to all of this is non-linear computer editing. In traditional video editing you copy segments of your rushes tape to your master tape - laying shots in order linearly onto your tape. Get to the end of a sequence and decide that you want to change the 3rd shot and you have to edit the entire sequence all over again. Grrr! Film editing is non-linear. Because the picture and sound exist as pieces of celluloid and magnetic tape that you physically cut and splice together if you decide you don't like the 3rd shot in a sequence it is simple enough to cut it out and replace it. Computer editing combines the best of both worlds - no need hunt through rooms of film to find your shot and its equally able to edit sequences together in any order. Non-linear computer editing allows you manipulate movie clips like you would add and change words in a word-processor - simply CUT, COPY and PASTE your movie together! What you need to get into non-linear computer editing?
Computer - Suprise! Suprise! I'm assuming you already have one of these (it makes reading eXposure easier ;-> ). Any machine produced in the last couple of years should be pretty capable. Obviously the faster the processor the better (to allow transitions such as dissolves to be built quickly). Lots of RAM is nice - video applications tend to gobble it up. Having spare expansion slots such as a PCI slot is vital allowing you to add a video capture card. Video Capture Card - This allows you to plug your camcorder or VCR into your computer and sample and store (digitize) clips of video to your hard disk. Capture cards compress video converting it to a digital file format such as M-JPEG (Motion JPEG) or DV (Digital Video). There's a variety of video capture cards - prices range from £150 - £5000+ depending on the quality of video and whether you want transitions and effects processed in realtime (rather than having to wait for the computer to build dissolves etc). If you are using Hi8 or S-VHS use a card with S-video input for the best quality. Likewise use a Firewire card for DV camcorders. Big Hard Drive - Once your video is digitized it starts taking up a lot of disk space - typically between 1.5Mb - 4Mb per second!! You can expect to see disk space disappearing rapidly as video clips start to colonise your hard disk. Its important to have a fast hard drive too - the drive needs to be able to record 3 to 4 megabytes worth of information every second. If it isn't up to the job it will start to drop frames ie. it will skip frames resulting in glitches and ocasionally jerky video. The solution is to buy a dedicated AV hard drive - the bigger and faster the better. More storage! - As you work on projects you may want to store and archive clips to work on in the future. Pound per megabyte the cheapest method currently is Recordable CD. For a quid you can store 650Mb (Jaz Drives can store a Gigabyte of data but Jaz cartridges are £40 whilst DVD-Ram drives can store 5.2Gb for £30) CD recorders also allow you to produce soundtrack CDs, enhanced CDs and send video clips to people around the world for negligible cost. Video
Compression, Data Rates and Disk Usage for Full
Size PAL video Video
Quality Compression Megabytes
per second Minutes
per Gigabyte VHS/8mm
minimum 15:1
1.4 12
S-VHS/Hi8
minimum 10:1 2.1 8 S-VHS/Hi8
recommended 7:1 3 5 DV 5:1 3.6 4 Non-linear editing software - Software usually comes bundled with the card. Get a powerful, flexible package that is easy to work with. Names to look out for include Adobe Premiere, Ulead MediaStudio, Judgement, EditDV and Avid. I prefer Premiere as its pretty powerful stuff and there's a lot you can do with it.
The Setup  Apologies for the above diagram - if at first glance it looks like a mess of cables then you're right...it is!! If you start wiring your computer equipment up to your video equipment its not long before everything disappears under a mountain of leads and power cables.
Digital Video Edit Suite (the RED lines) Using my setup as an example I have my camera (a Sony VX700) connected to my computer with a Firewire cable. MiniDV cameras compress the picture before recording the signal to tape producing broadcast quality pictures and CD-quality sound. The picture information is stored on the tape in a series of 1's and 0's (ie. its digital). To get the most out of DV, clips are transferred to the computer's hard disk using Firewire (also called IEEE 1394 and iLink). Firewire consists of a cable and an interface card (Radius's MotoDV in this case). You can control the camcorder from the computer and capture clips to the hard disk to edit. After editing the final movie can be sent back over the firewire cable to the camcorder. The movie file is of the same high quality as the original captured file. Digital In. Digital Out. Sounds great...in theory. Unfortunately there's an extra hurdle to cross if you're in the UK. The big selling point of DV was that there was no need to buy a DV VCR to record your final movie on - the camera could do the job through firewire. First the bad news - UK Firewire camcorders had DV IN deactivated due to EU import taxes. The only solution at the time was to buy a £3000 DV VCR (ouch!). Now the good news! DV IN can be reactivated on some camcorders by reprogramming the camera's memory. Thankfully we can skip the science bit as companies like Datavision produce a widget that connects to your camcorder and allows you to switch codes to enable DV IN. And the even better bit of good news is that in recent months camcorder manufacturers have seen sense and released UK DV camcorders with DV IN as standard. Remember to check before you buy. The final step is to transfer from the MiniDV master tape to VHS using the camcorder's phono outputs. Tadaaa!! One edited VHS copy of your movie.
Analog Video Non-Linear Edit Suite (the BLUE lines) What if you have a analog camcorder?...a Hi8, 8mm or S-VHS. You can still edit digitally but first you have to capture from your camcorder. If you are using a hi-band camcorder (Hi8, S-VHS, S-VHS-C) and your camcorder has an S-video output use a capture card with an S-video input for the best quality. Low-band camcorder users (8mm, VHS, VHS-C) might as well save themselves the expense and use the phono outputs. The quality you capture at depends on the quality you want your final movie. There's a couple of settings you can vary including the screen size (smaller if your final movie is for CD-Rom or the internet), frame rate (again fewer for CD-Rom or internet movies), audio sample rates and image compression. The capture card samples the picture and sound data and compresses it to store on your hard disk. The files produced are called M-JPEG files (Motion-JPEG). Again you edit non-linearly using software such as Premiere and produce a final movie file. The final movie file is transferred to directly to VHS (or if you have access a high band tape format such as Betacam or S-VHS). Here there is generation loss. The original image and the final image suffer slight degredation as the image has had to be sampled and copied. However this effect is minimal.
Now we know what kit we are using we will look at non-linear editing in practice. Next time we'll get our hands dirty; capturing and editing some footage in Premiere, going from our rushes to a final edited movie, all within the digital realm. How
compression works Audio
capture works by taking slices out of your
sound files. The greater the audio setting the more
slices it takes. For example 44KHz is CD-quality
sound whilst 22KHz Nicam stereo sound takes up half
as much disk space. Done sensibly sound settings
can be lowered considerably before you can hear the
drop in quality. Again compression can be applied
to decrease file sizes.
Would
you like to know more? To keep up to date with
developments in digital video subscribe to the
following. *So why is this article also called 'Let Dead Horses Sleep'? It's a silly joke really. One of the components of film is gelatine which is made by boiling down horse carcasses. There are no vegetarian film-makers. In the move to digital technology film is getting left behind and as such we can let dead horses sleep. |
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Suppose
you had a shot of your main character finding a
dead body in the snow (hey! this sounds like a good
movie - let's call it Fargo). The camera is
on a tripod and pretty steady so the only thing
moving in shot is Frances McDormand. Compression
works by mathematically describing reduntant areas
so instead of the computer's file saying 'snowy
white pixel...snowy white pixel...snowy white
pixel...snowy white pixel...snowy white pixel...'
it says 'bunch of snowy white pixels this big' and
the file takes up less space on your hard disk. The
only real work it has to do in a scene like that is
say 'Frances McDormand moves up a bit'.
Unfortunately the more the compression ratio is
increased the greater the chance of artefacts
appearing. Artefacts may include blockiness,
especially around the edges of objects.
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