# Offline Editing
Back in the old days of computer-based film editing, computers were,
famously, less powerful than the mobile phone in your pocket, and yet
people were able to edit higher-than-HD-resolution film for
international film releases. How was this possible?
Before answering that, a brief and simplified technical lesson:
Most films today are either all or mostly digital, both in the way they
are shot and edited. Before digital cameras took over, though, and in
some pockets of the filmmaking community today, celluloid film was used.
The celluloid film that you put into your camera and shoot is called
your *negative*: it is your original, master copy. Should anything
happen to your film negative, then entire days or weeks of filmmaking
would be lost (and depending on what you filmed, the footage might
literally be irreplaceable), which generally means that a lot of money
is lost, too. For those reasons, the negatives of a movie are protected
at any cost.
To ensure a negative\'s safety, it\'s promptly developed after being
shot, and then immediately copied to another reel of film. This copy is
called a *work print* (actually, there are several stages of copies,
here, but I\'m keeping it simple to better illustrate a point). The
negative is taken to a vault and stored safely away, and the movie
editor receives a work print.
For months, the movie editor re-creates the story told by the script
with the working-copy of the footage. If the work print gets too
scratched or is cut up too much to be useful, another copy can be made
from the original. The point is that the editor works on a work print
and *never* touches the negative.
The problem is, once the edit is done, it\'s been handled and spliced up
and taped together with tape; it\'s nowhere near theatrical quality. So
what do you do? you do a matchback: you take the edge numbers of the
work print and record the order in which you have spliced them together,
and then print yet a *new* copy of the movie in the proper order, from
the original, un-touched and pristine, negative.
## Digital Proxies
I explain this arcane (and yet not so arcane) technology to you because
it directly relates to the concept of *offline editing* in the digital
(and Digital Intermediate) world. Computer vendors don\'t really
advertise what their products are not capable of doing, so it\'s pretty
common for us to hear ads for the latest and greatest computers
promising us that we can \"edit HD video in realtime!\". There\'s some
truth to this; modern can edit video a lot better than ever before, but
you don\'t have to be an industry analyst to know that video cameras are
constantly dumping more information into the frame every year, too.
It\'s like a personal Cold War trying to keep a computer powerful enough
to process your video.
You might think that movie studios solve this problem by throwing money
at it. While that\'s partly true, even movie studios don\'t relish
throwing money away, so the way that professional editors *actually*
deal with the issue is with offline editing. It\'s a technique that\'s
been around since the beginning of computer-based editing, and it\'s a
technique that, in spite of the advertisements claiming otherwise, is
still useful in today\'s world.
Offline editing builds upon the idea of work prints in the celluloid
legacy model. Consider the footage that you shoot, at a high resolution,
your digital negative. You import it into your computer as normal, you
back it up as usual (because you back up your production drive at least
nightly, yes?), and bring it into Kdenlive. But you don\'t edit it.
Kdenlive creates proxy clips (or \"offline media\", as it is commonly
called in the industry). You can choose the resolution of your proxy
media; I frequently work at 640x480 scaled down from full 1920x1080 HD,
but if you need less drastic differential, then you might try working at
720p or similar. Working at this lower resolution permits your computer
to do far fewer calculations to move media around within your project,
when applying and playing back effects and transitions, and test
renders. In fact, you will quite probably find that your computer now
runs all processes in what will feel like realtime. Once your edit is
finished, you render your final product and Kdenlive magically knows not
to render out the proxy media, but to use the full resolution source
clips instead.
Kdenlive takes care of most of this for you, but you do have to ask it
to create the proxy media for you. Understand that most video editing
applications offline or proxy media, although most of them don\'t
involve the user in the process, instead doing it as necessary to
maintain the illusion that the software can just magically handle
heavyweight media without compromising in work quality. Don\'t be fooled
by the fact that you have to tell Kdenlive to use its proxy system;
it\'s not you, it\'s not your computer, it\'s not your software. It\'s
just honest and pragmatic computing.
## Proxy Walkthrough
To prove that the proxy process is a lot less scary than it sounds,
here\'s a quick walkthrough of the process, from project creation to
final render.
### Setup
The first step is the usual project creation sequence I have recommended
since my very first Kdenlive article: open Kdenlive, start and save a
fresh, empty project, and then import your footage. In that order.
I am a proponent of creating a new project, and then saving that
project, as your first step so that you establish a project directory
where all files (like auto-generated proxy files, which are particularly
relevant to this article) will be saved. So don\'t just start working,
and don\'t just save the default project; go to the **File** menu \>
**New**.
If you want to use proxies for an existing project, you can set this all
up from the **Project** menu \> **Project Settings**.
In the top section of the **Project Settings** window, designate a
**Project folder**. This is important, because it is where your proxy
clips will be stored and referenced by Kdenlive. Personally, I prefer to
create a unique project directory for every project.
For the video profile, do *not* use the video profile of your master
footage. Instead, use the video profile of the proxy clips you want to
generate. This is important! If you use the same resolution as your
source footage, then using proxies is not beneficial; you\'re
up-res\'ing footage to the same high quality video you are trying to
avoid. So use your *proxy resolution*, not your source resolution.
To be clear: if you shot at 1080p and you want to end up with 720p and
1080p distributable videos, but you want to work at a simple SD
(640x480, for example) resolution, then your project setting should be
VGA NTSC. When you render, you will be rendering out full quality clips.
I promise.
Next, place a tick in the **Proxy clips** section to activate offline
editing. You can set the threshold required for Kdenlive to generate
proxy clips and click the **OK** button.
Your project has now been saved, and the proxy system is active.
### Import Footage
Next, import your source material. You should probably save your source
material in your active Kdenlive project directory to keep your work
consolodated and easily archived, but it depends on your infrastructure
and workflow.
If a clip is larger than the threshold you set in **Project Settings**,
a proxy clip will be generated for you. You can always tell when a proxy
clip has been generated by the **P** icon in the upper left of the
thumbnail.
### Edit
At this point, you have simply to edit your project as usual. You will
find a remarkable boost in performance; all clips should play pretty
smoothly even with stacks and stacks of effects.
You should not do colour correction on proxy clips, because offlined
media is necessarily compressed, so any colour correction would be done
on an incomplete image. I also refrain from elaborate keyframing or
titling during the offline edit stage, for fear of subtle alignment
shifts when returning to full quality.
### Render
In an offline edit, there are two paths you might take when rendering.
You can render out the low res proxies, if you are just looking to get a
feel for how edits play, or you just need a reference video to use
during the [audio
mix](https://opensource.com/life/15/9/audio-and-video-xjadeo){target="_blank"}.
Or you might do a full quality render, tossing the proxy clips aside.
To start a render, click the **Render** button in the Kdenlive toolbar
or select **Project** menu \> **Render**.
If you are doing a test render, then set the target video profile to
whatever codec you prefer, and tick the **Render using proxy clips**
option.
If you want a full quality render, then set the target video profile to
whatever codec you prefer, and leave the **Render using proxy clips**
unticked. You can do variations of this by setting a new target size if
you want to render out a smaller version of your project (such as a 720p
version of the 1080p source). The point is that all originating data,
whether raw or through filters and effects, come from the full
resolution source footage and not from the proxy clips.
## Offline Editing in the Real World
Offline editing is a reality of digital editing, just as work prints
were a reality of celluloid. Whether you are required to switch it on
manually or whether it\'s done behind the magic curtain, it happens in
any editing system and it\'s something you should not just get familiar
with, not just get comfortable with, but learn to enjoy. It\'s a great
way to free up resources on your workstation, to make your editing
experience smoother, and in the professional realm where ultra-high
resolutions are common, it\'s an absolute necessity. But best of all, it
gets you editing faster and more efficiently so you can concentrate on
being creative.