Manual tweaks.

[dcpomatic.git] / doc / manual / dcpomatic.xml

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<bookinfo>
<title>DCP-o-matic</title>
<author><firstname>Carl</firstname><surname>Hetherington</surname></author>
</bookinfo>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Introduction</title>

<para>
Hello, and welcome to DCP-o-matic!
</para>

<section>
<title>What is DCP-o-matic?</title>

<para>
DCP-o-matic is a program to generate <ulink
url="http://en.wikipedia.org/wiki/Digital_Cinema_Package">Digital
Cinema Packages</ulink> (DCPs) from DVDs, Blu-Rays, video files such as MP4
and AVI, or still images.  The resulting DCPs will play on modern digital
cinema projectors.
</para>

<para>
You might find it useful to make DVDs easier to present, to encode
independently-shot feature films, or to generate local advertising for
your cinema.
</para>

</section>

<section>
<title>Licence</title>

<para>
DCP-o-matic is licensed under the <ulink url="http://www.gnu.org/licenses/old-licenses/gpl-2.0.html">GNU GPL</ulink>.
</para>

</section>

<section>
<title>Acknowledgements</title>

<para>
This manual uses icons from the <ulink url="http://tango.freedesktop.org/">Tango Desktop Project</ulink>, with thanks.
</para>

</section>
</chapter>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Installation</title>

<section>
<title>Windows</title>

<para>
To install DCP-o-matic on Windows, download the installer from
<ulink url="http://dcpomatic.com/">http://dcpomatic.com/</ulink>
and double-click it.  Click through the installer wizard, and
DCP-o-matic will be installed onto your machine.
</para>

<para>
If you are using a 32-bit version of Windows, you will need the 32-bit
installer.  For 64-bit Windows, either installer will work, but I
suggest you used the 64-bit version as it will allow DCP-o-matic to
use more memory.  You may find that DCP-o-matic crashes if you run
many parallel encoding threads (more than 4) on the 32-bit
version.
</para>

</section>

<section>
<title>Mac OS X</title>

<para>
DCP-o-matic will run on Mac OS X version 10.6 (Snow Leopard) and
higher.  To install it, download the <code>DMG</code> from <ulink
url="http://dcpomatic.com/">http://dcpomatic.com/</ulink> and double
click to open it.  Then drag the DCP-o-matic icon to your
<guilabel>Applications</guilabel> folder or wherever else you would
like to install it.
</para>

</section>

<section>
<title>Ubuntu Linux</title>

<para>
You can install DCP-o-matic on Ubuntu 12.04 (&lsquo;Precise
Pangolin&rsquo;), 12.10 (&lsquo;Quantal Quetzal&rsquo;), 13.10 (&lsquo;Saucy
Salamander&rsquo;) or 14.04 (&lsquo;Trusty Tahr&rsquo;) using <code>.deb</code> packages: download the
appropriate package from <ulink
url="http://dcpomatic.com/">http://dcpomatic.com/</ulink> and
double-click it.  Ubuntu will install the necessary bits and pieces
and set DCP-o-matic up for you.
</para>

</section>

<section>
<title>Debian Linux</title>
<para>
Packages are available for Debian 7 (squeeze) from <ulink
url="http://dcpomatic.com/">http://dcpomatic.com/</ulink>.
</para>
</section>

<section>
<title>Centos Linux</title>
<para>
Packages are available for Centos 6.5 from <ulink
url="http://dcpomatic.com/">http://dcpomatic.com/</ulink>.
</para>
</section>

<section>
<title>Arch Linux</title>
<para>
Packages for Arch Linux are available from <ulink
url="https://aur.archlinux.org/packages/dcpomatic/">https://aur.archlinux.org/packages/dcpomatic/</ulink>,
thanks to Stefan Karner.
</para>
</section>

<section>
<title>Other Linux distributions</title>

<para>
Installation on non-Ubuntu Linux is currently a little involved, as
there are no packages available (yet); you will have to compile it
from source.  If you are using a non-Ubuntu distribution, do let me
know via the <ulink url="mailto:carl@dcpomatic.com">mailing
list</ulink> and I will see about building some packages.
</para>

<para>
The following dependencies are required:
<itemizedlist>
<listitem><ulink url="http://ffmpeg.org/">FFmpeg</ulink></listitem>
<listitem><ulink url="http://www.mega-nerd.com/libsndfile/">libsndfile</ulink></listitem>
<listitem><ulink url="http://www.openssl.org/">OpenSSL</ulink></listitem>
<listitem><ulink url="http://www.openjpeg.org/">libopenjpeg</ulink></listitem>
<listitem><ulink url="http://www.imagemagick.org/script/index.php">ImageMagick</ulink></listitem>
<listitem><ulink url="http://www.boost.org/">Boost</ulink></listitem>
<listitem><ulink url="http://www.libssh.org/">libssh</ulink></listitem>
<listitem><ulink url="http://www.gtk.org/">GTK (on Linux)</ulink></listitem>
<listitem><ulink url="http://www.wxwidgets.org/">wxWidgets</ulink></listitem>
<listitem><ulink url="http://freecode.com/projects/libquickmail">libquickmail</ulink></listitem>
<listitem><ulink url="http://libxmlplusplus.sourceforge.net/">libxml++</ulink></listitem>
<listitem><ulink url="http://www.aleksey.com/xmlsec/">xmlsec</ulink></listitem>
<listitem><ulink url="http://curl.haxx.se/">curl</ulink></listitem>
<listitem><ulink url="http://www.nih.at/libzip/">libzip</ulink></listitem>
<listitem><ulink url="http://carlh.net/software/libdcp/">libdcp</ulink></listitem>
<listitem><ulink url="http://carlh.net/software/libcxml/">libcxml</ulink></listitem>
</itemizedlist>
</para>

<para>
Once you have installed the development packages for the dependencies,
download the source code from <ulink
url="http://dcpomatic.com/">http://dcpomatic.com/</ulink>,
unpack it and run the following commands from inside the source
directory:
</para>

<programlisting>
./waf configure
./waf build
sudo ./waf install
</programlisting>

<para>
With any luck, this will build and install DCP-o-matic on your system.  To run it, enter:
</para>

<programlisting>
dcpomatic
</programlisting>

<para>
in a shell.
</para>

</section>
</chapter>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Creating a video DCP</title>

<para>
In this chapter we will see how to create a video DCP using
DCP-o-matic.  We will gloss over the details and look at the basics.
</para>

<section>
<title>Creating a new film</title>

<para>
Let's make a very simple DCP to see how DCP-o-matic works.  First, we
need some content.  Download the low-resolution trailer for the open
movie <ulink url="http://sintel.org/">Sintel</ulink> from <ulink
url="http://ftp.nluug.nl/ftp/graphics/blender/apricot/trailer/Sintel_Trailer1.480p.DivX_Plus_HD.mkv">their
website</ulink>.  Generally, of course, one would want to use the
highest-resolution material available, but for this test we will use
the low-resolution version to save everyone's bandwidth bills.
</para>

<para>
Now, start DCP-o-matic and its window will open.  First, we will
create a new &lsquo;film&rsquo;.  A &lsquo;film&rsquo; is how DCP-o-matic refers to
some pieces of content, along with some settings, which we will make into
a DCP.  DCP-o-matic stores its data in a folder on your disk while it
creates the DCP.  You can create a new film by selecting
<guilabel>New</guilabel> from the <guilabel>File</guilabel> menu, as
shown in <xref linkend="fig-file-new"/>.
</para>

<figure id="fig-file-new">
  <title>Creating a new film</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/file-new&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
This will open a dialogue box for the new film, as shown in <xref
linkend="fig-video-new-film"/>.
</para>

<figure id="fig-video-new-film">
  <title>Dialogue box for creating a new film</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/video-new-film&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
In this dialogue box you can choose a name for the film.  This will be
used to name the folder to store its data in, and also as the initial
name for the DCP itself.  You can also choose whereabouts you want to create
the film.  In the example from the figure, DCP-o-matic will create a
folder called &lsquo;DCP Test&rsquo; inside my home folder (carl) into which it
will write its working files.
</para>

</section>

<section>
<title>Adding content</title>

<para>
The next step is to add the content that you want to use.  DCP-o-matic
can make DCPs from multiple pieces of content, but in this simple
example we will just use a single piece.  Click the <guilabel>Add
file(s)...</guilabel> button, as shown in <xref
linkend="fig-add-file"/>, and a file chooser will open for you to
select the content file to use, as shown in <xref
linkend="fig-video-select-content-file"/>.
</para>

<figure id="fig-add-file"> 
  <title>Adding content files</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/add-file&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<figure id="fig-video-select-content-file"> 
  <title>Selecting a video content file</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/video-select-content-file&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
Select your content file and click <guilabel>Open</guilabel>.  In this
case we are using the Sintel trailer that we downloaded earlier.
</para>

<para>
When you do this, DCP-o-matic will take a look at your file.  After a
short while (when the progress bar at the bottom right of the window
has finished), you can look through your content using the slider to
the right of the window, as shown in <xref linkend="fig-examine-content"/>.
</para>

<figure id="fig-examine-content"> 
  <title>Examining the content</title>
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/examine-content&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
Dragging the slider will move through your video.  You can also click
the <guilabel>Play</guilabel> button to play the content back.  Note
that there will be no sound, and playback might not be entirely
accurate (it may be slightly slower or faster than it should be, for
example).  This player is really only intended for brief inspection of
content; if you need to check it more thoroughly, use another player
such as <ulink
url="http://projects.gnome.org/totem/index.html">Totem</ulink>, <ulink
url="http://www.mplayerhq.hu/design7/news.html">mplayer</ulink> or
<ulink url="http://www.videolan.org/vlc/index.html">VLC</ulink>.
</para>

</section>



<section>
<title>Making the DCP</title>

<para>In most cases, some adjustments would be made to DCP-o-matic's
settings once the content has been added.  For our simple test,
however, the default values will suffice, so we can go straight onto
making the DCP.</para>

<para>
Choose <guilabel>Make DCP</guilabel> from the
<guilabel>Jobs</guilabel> menu.  DCP-o-matic will encode your DCP.
This may take some time (many hours in some cases).  While the job is
in progress, DCP-o-matic will update you on how it is getting on with
the progress bar in the bottom of its window, as shown in <xref
linkend="fig-making-dcp"/>.
</para>

<figure id="fig-making-dcp">
  <title>Making the DCP</title>
  <mediaobject>
    <imageobject> 
      <imagedata scale="30" fileref="screenshots/making-dcp&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
When it has finished, the DCP will end up on your disk inside the
film's folder.  You can then copy this to a projector via a USB
stick, hard-drive or network connection.  See <xref
linkend="ch-files"/> for details about the files that DCP-o-matic creates.
</para>

<para>
Alternatively, if you have a projector or TMS that is accessible via
SCP across your network, you can upload the content directly from
DCP-o-matic.  See the preferences in <xref linkend="sec-prefs-tms"/>.
</para>

</section>
</chapter>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Creating a still-image DCP</title>

<para>
DCP-o-matic can also be used to create DCPs of one or more still images, perhaps
for an advertisement or an on-screen announcement.  This chapter shows you
how to do it.
</para>

<para>
As with video DCPs, the first step is to create a new
&lsquo;Film&rsquo;; select <guilabel>New</guilabel> from the
<guilabel>File</guilabel> menu and the new film dialogue will open as
shown in <xref linkend="fig-still-new-film"/>.
</para>

<figure id="fig-still-new-film"> 
  <title>Dialogue box for creating a new film</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/still-new-film&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
Enter a name and click <guilabel>OK</guilabel>.  Now we need to add
the content.  As before, click <guilabel>Add file(s)...</guilabel>.
For our example, we will add a single image file, as shown in <xref
linkend="fig-still-select-content-file"/>.
</para>

<figure id="fig-still-select-content-file"> 
  <title>Selecting a still content file</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/still-select-content-file&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
As with video DCPs, most of the default settings will be fine for a
simple test.  The one thing that you might wish to change is the
length of the still.  Select the <guilabel>Timing</guilabel> tab and
you will see a <guilabel>Length</guilabel> setting, as shown in <xref
linkend="fig-timing-tab"/>.
</para>

<figure id="fig-timing-tab"> 
  <title>The timing tab</title>
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/timing-tab&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
This length is a &lsquo;timecode&rsquo;: it consists of four numbers.
The first is hours, the second minutes, the third seconds, and the
fourth frames.  Enter the duration that you want and then click <guilabel>Set</guilabel>.
</para>

<para>
Finally, as with video, you can choose <guilabel>Make DCP</guilabel>
from the <guilabel>Jobs</guilabel> menu to create your DCP.  This will
be much quicker than creating a video DCP, as DCP-o-matic only needs
to encode a single frame which it can then repeat.
</para>

</chapter>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Content settings</title>

<para>
The previous chapters showed DCP generation using the default
settings.  DCP-o-matic offers a range of features to adjust the
content that goes into your DCP, and this chapter describes those features in
detail.
</para>

<section>
<title>Adding and removing content</title>

<para>
At the top of the <guilabel>Content</guilabel> tab is a list of the
content that will go into our DCP.  There can be as many pieces of
content as you like, and they can be of the following types:
</para>

<itemizedlist>
<listitem>Movie &mdash; a file containing some video, probably some
audio and possibly some subtitles; for example, a MOV, MP4 or VOB.
</listitem>

<listitem>Sound &mdash; a file containing one or more channels of
audio; for example, a WAV or AIFF file.
</listitem>

<listitem>Still image &mdash; a file containing a single still image; for
example, a JPEG, PNG or TIFF file.
</listitem>

<listitem>Moving image &mdash; a directory containing many still
images which should be treated as the frames of a video.
</listitem>
</itemizedlist>

<para>
To add one or more movie, sound or still-image files, select
<guilabel>Add file(s)...</guilabel> and choose them from the selector.
To add a directory of images, choose <guilabel>Add
directory...</guilabel> and do similar.
</para>

<para>
You can remove a piece of content by clicking on its name and then
clicking the <guilabel>Remove</guilabel> button.
</para>

</section>
<section>
<title>Content Properties</title>

<para>
Below the content list are the controls to set content properties.  To
adjust the properties for a piece of content, click its name in the
content list.  The content property controls will then become active
for that piece of content.
</para>

<para>
The content properties are split up into four sections:
<guilabel>Video</guilabel>, <guilabel>Audio</guilabel>,
<guilabel>Subtitles</guilabel> and <guilabel>Timing</guilabel>.  Not
all of these sections will be active for all content types.  The controls
in each section are described below.
</para>

</section>

<section>
<title>Video</title>

<para>
The <guilabel>Video</guilabel> tab controls properties of the image, as shown in <xref linkend="fig-video-tab"/>.
</para>

<figure id="fig-video-tab"> 
  <title>Video settings tab</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/video-tab&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<section>
<title>Image type</title>

<para>
The first option on this tab is the &lsquo;type&rsquo; of the video.
This specifies how DCP-o-matic should interpret the video's image.
<guilabel>2D</guilabel> is the default; this just takes the video
image as a standard 2D frame.  The <guilabel>3D
left/right</guilabel> option tells DCP-o-matic to interpret the frame as a
left-right pair, as shown in <xref linkend="fig-3d-left-right"/>.
</para>

<figure id="fig-3d-left-right"> 
  <title>3D left/right image type</title>
  <mediaobject>
    <imageobject> 
       <imagedata scale="100" fileref="diagrams/3d-left-right&dia;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
Alternatively the <guilabel>3D top/bottom</guilabel> option tells
DCP-o-matic to see the frame as a top-bottom pair, as shown in <xref
linkend="fig-3d-top-bottom"/>.
</para>

<figure id="fig-3d-top-bottom"> 
  <title>3D top/bottom image type</title>
  <mediaobject>
    <imageobject> 
       <imagedata scale="100" fileref="diagrams/3d-top-bottom&dia;"/>
    </imageobject> 
  </mediaobject>
</figure>

</section>


<!-- ============================================================== -->
<section>
<title>Filtering</title>

<para>
The &lsquo;filters&rsquo; settings allow you to apply various video
filters to the image.  These may be useful to try to improve
poor-quality sources like DVDs.  You can set up the filters by clicking the
<guilabel>Edit</guilabel> button next to the filters entry in the
setup area of the DCP-o-matic window; this opens the filters selector
as shown in <xref linkend="fig-filters"/>.
</para>

<figure id="fig-filters"> 
  <title>Filters selector</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/filters&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
After changing the filters setup, you will need to regenerate the DCP
to see the effect on the cinema screen.  The preview in DCP-o-matic
will update itself whenever filters are changed, though of course this
image is much smaller and of lower resolution than a projected image!
</para>
</section>


<!-- ============================================================== -->
<section>
<title>Other settings</title>

<para>
The &lsquo;crop&rsquo; settings can be used to crop your content,
which can be used to remove black borders from round the edges of DVD
images, for example.  The specified number of pixels will be trimmed
from each edge, and the content image in the right of the window will
be updated to show the effect of the crop.
</para>

<para>
The <guilabel>Scale to</guilabel> option governs the shape that
DCP-o-matic will scale the content's image into.  Select the aspect
ratio that your content should be presented in.
</para>

</section>
<section>
<title>Video description</title>

<para>
At the bottom of the video tab is a short description of what will
happen to your video with the current settings.  In the example of
<xref linkend="fig-video-tab"/>, DCP-o-matic is telling you that the
video file is 1920x1080 pixels (which is a ratio of 1.78:1).  Since
the controls specify &lsquo;Flat&rsquo; for the ratio, DCP-o-matic
scales the content image to 1998x1080, which is the DCI flat
resolution at 2K.
</para>

<para>
This description also gives the frame rate of the content and what
will happen to it when it is played at the DCP's frame rate.
<!-- XXX: link to more detailed discussion of this -->
</para>

</section>

</section>

<section>
<title>Audio</title>

<para>
The <guilabel>Audio</guilabel> tab controls properties of the image, as shown in <xref linkend="fig-audio-tab"/>.
</para>

<figure id="fig-audio-tab"> 
  <title>Audio settings tab</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/audio-tab&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<section>
<title>Show audio</title>

<para>
The <guilabel>Show Audio</guilabel> button will instruct DCP-o-matic
to examine the audio in your content and plot a graph of its level
over time.  This can be useful for getting a rough idea of how loud
the sound will be in the cinema auditorium.  A typical plot is shown
in <xref linkend="fig-audio-plot"/>
</para>

<figure id="fig-audio-plot"> 
  <title>Audio plot</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/audio-plot&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
The plot gives the audio level (vertical axis, in dB) with time
(horizontal axis).  0dB represents full scale, so if there is anything
near this you are in danger of clipping the projector's audio outputs.
</para>

<para>
There are two plot types: the peak level and the RMS, which can be
shown or hidden using the check-boxes on the right hand side of the
window.
</para>

<para>
The channel check-boxes will show or hide the plot(s) for
the corresponding channels in the DCP.
</para>

<para>
The smoothing slider applies a variable degree of temporal smoothing
to the plots, which can make them easier to read in some cases.
</para>

<para>
Obviously the audio plot is no substitute for listening in an
auditorium, but it can be useful to get levels in the right rough area.
</para>

</section>

<section>
<title>The audio map</title>

<para>
The section at the bottom of the audio tab is the &lsquo;audio
map&rsquo;.  This governs how sound from the content will be arranged
in the DCP.
</para>

<para>
Down the left-hand side of the map is the list of audio channels in
the currently-selected piece of content.  Along the top is each
channel in the DCP.  A checked box means that the corresponding
content channel will be copied into the corresponding DCP channel.
</para>

<para>
Consider, for example, the case in <xref linkend="fig-audio-map-eg1"/>.
</para>

<figure id="fig-audio-map-eg1">
  <title>Audio map example 1</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/audio-map-eg1&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
Here, we have two channels in the source which are mapped to left and
right, respectively, in the DCP.  If we modify that as in <xref
linkend="fig-audio-map-eg2"/>
</para>

<figure id="fig-audio-map-eg2">
  <title>Audio map example 2</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/audio-map-eg2&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
we now have the content's streams mapped to left and right and also
mixed together and placed in the DCP's centre channel.
</para>

<figure id="fig-audio-map-eg3">
  <title>Audio map example 3</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/audio-map-eg3&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
As a final example, the map in <xref linkend="fig-audio-map-eg3"/>
shows the mapping of a 5.1 source into a 5.1 DCP.
</para>

</section>

<section>
<title>Other controls</title>

<para>
&lsquo;Audio Gain&rsquo; is used to alter the volume of the
soundtrack.  The specified gain (in dB) will be applied to each sound
channel of your content before it is written to the DCP.
</para>

<para>
If you use a sound processor that DCP-o-matic knows about, it can help
you calculate changes in gain that you should apply.  Say, for
example, that you make a test DCP and find that you have to run it at
volume 5 instead of volume 7 to get a good sound level in the screen.
If this is the case, click the <guilabel>Calculate...</guilabel>
button next to the audio gain entry, and the dialogue box in <xref
linkend="fig-calculate-audio-gain"/> will open.
</para>

<figure id="fig-calculate-audio-gain"> 
  <title>Calculating audio gain</title>
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/calculate-audio-gain&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
For our example, put 5 in the first box and 7 in the second and click
<guilabel>OK</guilabel>.  DCP-o-matic will calculate the audio gain
that it should apply to make this happen.  Then you can re-make the
DCP (this will be reasonably fast, as the video data will already have
been done) and it should play back at the correct volume with 7 on
your sound-rack fader.
</para>

<para>
Current versions of DCP-o-matic only know about the Dolby CP650 and
CP750.  If you use a different sound processor, and know the gain
curve of its volume control, <ulink url="mailto:carl@dcpomatic.com">get in
touch</ulink>.
</para>

<para>
<guilabel>Audio Delay</guilabel> is used to adjust the synchronisation
between audio and video.  A positive delay will move the audio later
with respect to the video, and a negative delay will move it earlier.
</para>

<para>
The <guilabel>Audio Stream</guilabel> option allows you to select the
audio stream to use, if the content contains more than one.  There
might be different soundtrack languages, for example.
</para>

</section>
</section>


<section>
<title>Subtitles</title>

<para>
The subtitles tab contains settings related to subtitles in your
content, as shown in <xref linkend="fig-subtitles-tab"/>.
</para>

<figure id="fig-subtitles-tab"> 
  <title>Subtitle settings tab</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/subtitles-tab&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
DCP-o-matic will extract subtitles from the content, if present, and
they can be &lsquo;burnt into&rsquo; the DCP (that is, they are
included in the image and not overlaid by the projector).  Note that
DVD and Blu-Ray subtitles are stored as bitmaps, so it is not possible
(automatically) to use non-burnt-in subtitles with these sources.
Select the <guilabel>With Subtitles</guilabel> check-box to enable
subtitles.  The <guilabel>offset</guilabel> control moves the
subtitles up and down the image, and the <guilabel>scale</guilabel>
control changes their size.
</para>

<para>
All being well, future versions of DCP-o-matic will include the option to
use text subtitles (as is the norm with most professionally-mastered
DCPs).
</para>

</section>

<!-- XXX: timing tab -->

</chapter>

<chapter xml:id="ch-dcp" xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>DCP settings</title>

<para>
This chapter describes the settings that apply to the whole DCP.  The
controls for these settings are in the <guilabel>DCP</guilabel> tab of
the main window, as shown in <xref linkend="fig-dcp-tab"/>.
</para>

<figure id="fig-dcp-tab"> 
  <title>DCP settings tab</title>
  <mediaobject>
    <imageobject> 
       <imagedata fileref="screenshots/dcp-tab&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
The first thing here is the name.  This is generally set to the title
of the film that is being encoded.  If <guilabel>Use DCI
name</guilabel> is not ticked, the name that you specify will be used
as-is for the name of the DCP.  If <guilabel>Use DCI name</guilabel>
is ticked, the name that you enter will be used as part of a
DCI-compliant name.  
</para>

<para>
Underneath the name field is a preview of the name that the DCP will
get.  To use a DCI-compliant name, tick the <guilabel>Use DCI
name</guilabel> check-box.  The DCI name will be composed using details
of your content's soundtrack, the current date and other things that
can be specified in the DCI name details dialogue box, which you can
open by clicking on the <guilabel>Details</guilabel> button.
</para>

<para>
If the DCP name is long, it may not all be visible.  You can see the
full name by hovering the mouse pointer over the partial name.
</para>

<para>
The <guilabel>Container</guilabel> option sets the ratio of the image
in the DCP.  If this ratio is different to the ratio used for any
content, DCP-o-matic will pad the content with black.  In simple cases
this should be set to the same ratio as that for the the primary piece
of video content.  Alternatively, you might want to pillarbox a small
format into a Flat container: in this case, select the small format
for the content's ratio and &lsquo;Flat&rsquo; for the DCP.
</para>

<para>
Next up is the content type.  This can be
&lsquo;feature&rsquo;, &lsquo;trailer&rsquo; or whatever; select the
required type from the drop-down list.
</para>

<para>
The <guilabel>Frame Rate</guilabel> control sets the frame rate of
your DCP.  This can be a little tricky to get right.  Ideally, you
want it to be the same as the video content that you are using.  If it
is not the same, DCP-o-matic must resort to some tricks to alter your
content to fit the specified frame rate.  Frame rates are discussed in
more detail in <xref linkend="ch-frame-rates"/>.
</para>

<para>
The <guilabel>Encrypted</guilabel> check-box will set whether the DCP
should be encrypted or not.  If this is ticked, the DCP will require a
KDM to play back.  Encryption is discussed in <xref
linkend="ch-encryption"/>.
</para>

<para>
The <guilabel>Use best</guilabel> button sets the DCP video frame rate
to what DCP-o-matic thinks is the best given the content that you have
added.
</para>

<para>
The <guilabel>Audio Channels</guilabel> control sets the number of
audio channels that the DCP will have.  If the DCP has any channels
for which there is no content audio they will be replaced by silence.
</para>

<para>
The <guilabel>3D</guilabel> button will set your DCP to 3D mode if it
is checked.  A 3D DCP will then be created, and any 2D content will be
made 3D compatible by repeating the same frame for both left and right
eyes.  A 3D DCP can be played back on many 3D systems (e.g. Dolby 3D,
Real-D etc.) but not on a 2D system.
</para>

<para>
The <guilabel>Resolution</guilabel> tab allows you to choose the
resolution for your DCP.  Use 2K unless you have content that is of
high enough resolution to be worth presenting in 4K.
</para>

<para>
The <guilabel>JPEG2000 bandwidth</guilabel>; setting changes how big the final
image files used within the DCP will be.  Larger numbers will give
better quality, but correspondingly larger DCPs.  The bandwidth can be
between 50 and 250 megabits per second (Mbit/s).
</para>

<para>
The <guilabel>Standard</guilabel> option specifies which of the two
DCP standards DCP-o-matic should use.  If in doubt, use SMPTE (the
more modern of the two).
</para>

<para>
Finally, the <guilabel>scaler</guilabel> is the method that will be used to scale up
your content to the required size for the DCP, if required.  Bicubic is a fine choice in
most situations.
</para>

</chapter>

<chapter xml:id="ch-encryption" xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Encryption</title>

<para>
It is not required that DCPs be encrypted, but they can be.  This
chapter discusses the basic principles of DCP encryption, and how
DCP-o-matic can create encrypted DCPs and KDMs for them.
</para>

<section>
<title>Basics</title>

<para>
DCPs can be encrypted.  This means that the picture and sound data are
encoded in such a way that only cinemas &lsquo;approved&rsquo; by the
DCP's creators can read them.  In particular, this means copies of the
DCP can be distributed by insecure means: if an ne'er-do-well called
Mallory obtains a hard drive containing an encrypted DCP, there is no
way that he can play it.  Only those cinemas who receive a key
delivery message (KDM) can play the DCP.
</para>

<section>
<title>How it works (in a nutshell)</title>

<para>
This section attempts to summarise how DCP encryption works.  You can
skip it if you like.  You may need some knowledge of encryption
methods to understand it.
</para>

<para>
We suppose that we are trying to distribute a DCP to
Alice's cinema, without a troublemaker called Mallory being able to
watch it himself.
</para>

<para>
There are two main families of encryption techniques.  The first,
symmetric-key encryption, allows us to encode some data using some
numeric key.  After encoding, no-one can decode the data unless they
know the key.
</para>

<para>
The first step in a DCP encryption is to encode its data with some key
using symmetric-key encryption.  The encrypted DCP can then be sent
anywhere, safe in the knowledge that even if Mallory got hold of a
copy, he could not decrypt it.
</para>

<para>
Alice, however, needs to know the key so she can play the DCP in her
cinema.  A simple approach might be for us to send Alice the key.
However, if Mallory can intercept the DCP, he might also be able to
intercept our communication of the key to Alice.  Furthermore, if Alice
happened to know Mallory, she could just send him a copy of the key.
</para>

<para>
The clever bit in DCP encryption requires the use of public-key
encryption.  With this technique we can encrypt a block of data using
some &lsquo;public&rsquo; key.  That data can then only be decrypted
using a <emphasis>different</emphasis> &lsquo;private&rsquo; key.  The
private and public keys are related mathematically, but it is
extremely hard (or rather, virtually impossible) to derive the private
key from the public key.
</para>

<para>
Public-key encryption allows us to distribute the DCP's key to Alice
securely.  The manufacturer of Alice's projector generates a public
and private key.  They hide the private key deep inside the bowels of
the projector (inside an integrated circuit) where no-one can read it.
They then make the public key available to anyone who is interested.
</para>

<para>
We take our DCP's symmetric key and encrypt it using the public key of
Alice's projector.  We send the result to Alice over email (using a
format called a Key Delivery Message, or KDM).  Her projector then
decrypts our message using its private key, yielding the magic
symmetric key which can decrypt the DCP.
</para>

<para>
If is fine if Mallory intercepts our email to Alice, since the only
key which can decrypt the message is the private key buried inside
Alice's projector.  The projector manufacturer is very careful that
no-one ever finds out what this key is.  Our DCP is secure: only Alice
can play it back, since only her projector knows the key (even Alice
does not).
</para>

</section>
</section>

<section>
<title>Encryption using DCP-o-matic</title>

<para>
There are two steps to distributing an encrypted DCP.  First, the
DCP's data must be encrypted, and secondly KDMs must be generated for
those cinemas that are allowed to play the DCP.
</para>

<para>
The first part is simple: ticking the <guilabel>Encrypted</guilabel>
box in the <guilabel>DCP</guilabel> tab of DCP-o-matic will encrypt
the DCP using a random key that DCP-o-matic generates.  The key will
be written to the film's metadata file, so that should be kept
secure.
</para>

<para>
A DCP that is generated with the <guilabel>Encrypted</guilabel> box
ticked will not play on any projector as-is (it will be marked as
&lsquo;locked&rsquo;, or whatever the projector manufacturer's term
is).
</para>

<para>
The second part is to generate KDMs for the cinemas that you wish to
allow to play your DCP.  This is done using the <guilabel>Make
KDMs</guilabel> option on the <guilabel>Jobs</guilabel> menu.  This
will open the KDM dialogue box, as shown in <xref linkend="fig-kdm"/>.
</para>

<figure id="fig-kdm">
  <title>KDM dialog</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/kdm&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
In order to generate KDMs for a particular projector, you need to know
its <emphasis>certificate</emphasis>.  These are usually made
available by the projector manufacturers as text files with a
<code>.pem</code> extension.
</para>

<para>
DCP-o-matic can store these certificates to make life easier.  It
stores details of cinemas and screens within those cinemas.  Each
screen has a certificate for its projector.  DCP-o-matic can generate
KDMs for any screens that it knows about.
</para>

<para>
To add a cinema, click <guilabel>Add Cinema...</guilabel>.  This opens
a dialogue box into which you can enter the cinema's name, and
optionally an email address.  This email address can be used to
get DCP-o-matic to deliver KDMs via email, but it is optional.
</para>

<para>
Once you have added a cinema, select it by clicking on its name, then
click <guilabel>Add Screen...</guilabel>.  The resulting dialogue
allows you to enter a name for the screen and load in its certificate
from a file.  The certificate should be in SHA256 PEM format.
</para>

<para>
Once you have set up all the screens that you need KDMs for,
DCP-o-matic can generate KDMs for the last DCP that you generated for
the currently-loaded film.  Select the cinemas and/or screens that you
want KDMs for and fill in the start and end dates and times.  
</para>

<para>
Finally, choose what you want to do with the KDMs.  They can be
written to disk, to a location that you can specify by clicking
<guilabel>Browse</guilabel>.  Alternatively, if you choose
<guilabel>Send by email</guilabel> the KDMs will be zipped up and
emailed to the appropriate cinema email addresses.  Click OK to
generate the KDMs.
</para>

</section>

</chapter>


<chapter xml:id="ch-preferences" xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Preferences</title>

<para>
DCP-o-matic provides a few preferences which can be used to modify its
behaviour.  This chapter explains those options.
</para>

<section>
<title>The preferences dialogue</title>

<para>
The preferences dialogue is opened by choosing
<guilabel>Preferences...</guilabel> from the <guilabel>Edit</guilabel>
menu.  The dialogue is split into five tabs.
</para>

<section>
<title>Miscellaneous</title>

<para>
The miscellaneous tab is shown in <xref linkend="fig-prefs-misc"/>.
</para>

<figure id="fig-prefs-misc"> 
  <title>Miscellaneous preferences</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/prefs-misc&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<section>
<title>Language</title>

<para>
If you tick the <guilabel>Set Language</guilabel> checkbox and choose
a language from the list, that language will be used for DCP-o-matic.
You will need to restart DCP-o-matic to see the new language.
</para>

<para>
The translations for DCP-o-matic have been contributed by helpful
users.  If your language is not on the last, head to <ulink
url="http://dcpomatic.com/i18n.php">the DCP-o-matic website</ulink> to
read about how to contribute a translation.
</para>
</section>

<section>
<title>Threads</title>

<para>
When DCP-o-matic is encoding DCPs it can use multiple parallel threads
to speed things up.  Set this value to the number of threads
DCP-o-matic should use.  This should normally be the number of
processors (or processor cores) in your machine.  DCP-o-matic will try
to set this up correctly when you run it for the first time.
</para>

</section>

<section>
<title>KDM emails</title>

<para>
DCP-o-matic can send KDMs (see <xref linkend="ch-encryption"/>) to
cinemas (or anywhere else) via email.  To make this work, enter a
suitable outgoing mail (SMTP) server and &lsquo;from&rsquo; address
for these emails.
</para>

</section>

<section>
<title>Defaults</title>

<para>
The next few options allow you to set up default values for several
properties of new films that you create.
</para>

</section>
</section>

<section>
<title>Colour conversions</title>

<para>
The colour conversions tab is shown in <xref linkend="fig-prefs-colour-conversions"/>.
</para>

<figure id="fig-prefs-colour-conversions">
  <title>Colour conversions preferences</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/prefs-colour-conversions&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
As part of the encoding process, DCP-o-matic has to convert the colour
space of the source files that you use into XYZ, the colour space used
by the DCI standard.
</para>

<para>
Colour conversion is discussed in more detail in a separate document
<ulink url="http://dcpomatic.com/manual/colour.pdf">colour.pdf</ulink>.
</para>

<para>
These preferences control a list of presets which are suitable for
converting from common input colour spaces to XYZ.
</para>

</section>

<section>
<title>Metadata</title>

<para>
The metadata tab is shown in <xref linkend="fig-prefs-metadata"/>.
</para>

<figure id="fig-prefs-metadata"> 
  <title>Metadata preferences</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/prefs-metadata&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
This allows you to set up a couple of identifiers that are written
into the DCP.  The default values should cause no problems.
</para>

</section>

<section xml:id="sec-prefs-tms">
<title>TMS</title>

<para>
The TMS tab (shown in <xref linkend="fig-prefs-tms"/>) gives some
options for specifying details about your theatre management system
(TMS).  If you do this, and your TMS accepts SSH connections, you can
upload DCPs directly from DCP-o-matic to the TMS using the
<guilabel>Send DCP to TMS</guilabel> option in the
<guilabel>Jobs</guilabel> menu.
</para>

<figure id="fig-prefs-tms"> 
  <title>TMS preferences</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/prefs-tms&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
<guilabel>TMS IP address</guilabel> should be set to the IP address of
your TMS, <guilabel>TMS target path</guilabel> to the place that DCPs
should be uploaded to (which will be relative to the home directory of
the SSH user).  Finally, the user name and password are the
credentials required to log into the TMS via SSH.
</para>
</section>

<section>
<title>KDM email</title>

<para>
The KDM email is shown in <xref linkend="fig-prefs-kdm-email"/>.
</para>

<figure id="fig-prefs-kdm-email"> 
  <title>KDM email preferences</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="screenshots/prefs-kdm-email&scs;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
This is a template for the email that is used to send KDMs out to
cinemas.  You can change it to say whatever you like.  The
&lsquo;magic&rsquo; string <code>$CPL_NAME</code> will be replaced by
DCP's title.
</para>

</section>
</section>

</chapter>

<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en" xml:id="ch-frame-rates">
<title>Frame rates</title>

<para>
In an ideal world, a DCP would be created using content at the same
video frame and audio sampling rates as the DCP.  This is not,
however, always possible.
</para>

<section>
<title>DCP rate limitations</title>

<para>
There are some limitations to video and audio rates in DCPs.  This is
complicated by the fact that not all projectors will play DCPs at the
same rates.  It is possible to create a DCP which one projector will
play fine, but another (of a different type) will refuse to play, or
even refuse to ingest.
</para>

<section>
<title>Guaranteed rates</title>

<para>
The only rates that are (pretty much) guaranteed to work on all DCI
projectors is 24 frames per second (fps) for video and 48kHz or 96kHz
for audio.  If you are sending your DCPs to unknown places it wise to
consider using these rates if at all possible.
</para>

</section>

<section>
<title>Other often-supported rates</title>
<para>
Many projectors now in the wild support additional video frame rates:
25, 30 and 48 fps.
</para>
</section>

<section>
<title>Adapting content to fit the DCP rate</title>

<para>
DCP-o-matic has a few tricks to allow you to use content that is not
in one of the &lsquo;approved&rsquo; rates.
</para>

<para>
Audio is easy: DCP-o-matic can resample to 48kHz from any source rate
with minimal loss in quality.
</para>

<para>
Video rate conversion is harder.  DCP-o-matic's basic strategy to deal
with a non-supported content rate is to run it at the wrong speed, and
to adjust the audio to keep it in sync.
</para>

<para>Let us consider the example of a 25fps source for which you want
to create a 24fps DCP.  DCP-o-matic will put the frames from the
source directly into the DCP without modification, but will tell the
projector to play them back at 24fps.  This means that the DCP's video
will run slightly slower than the original.
</para>

<para>
If DCP-o-matic did nothing else, the result of this would be that the
audio would be running at the original speed with the video running
slowly.  Hence the audio would drift slowly out of sync.  To avoid
this, DCP-o-matic also resamples the audio such that the projector
will play it too fast by the same amount.  Hence it will sound
slightly different but will remain in sync with the video.
</para>

<para>
For very low or high frame rates, DCP-o-matic can also skip or duplicate frames.
</para>

</section>
</section>

<section>
<title>Setting up</title>

<para>
The <guilabel>Frame Rate</guilabel> control in the
<guilabel>DCP</guilabel> tab sets the video frame rate that the DCP
will use.  Clicking <guilabel>Use best</guilabel> sets the rate to
what DVD-o-matic thinks is the best for your content.  With this
button, DCP-o-matic assumes that the whole range of frame rates (24,
25, 30 and 48fps) are allowable.
</para>

<para>
After this, the <guilabel>Video</guilabel> tab for each piece of
content will give a summary of what DCP-o-matic is doing with that
content.
</para>

</section>

</chapter>


<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en" xml:id="ch-servers">
<title>Encoding servers</title>

<para>
One way to increase the speed of DCP encoding is to use more
than one machine at the same time.  An instance of DCP-o-matic can
offload some of the time-consuming JPEG2000 encoding to any number of
other machines on a network.  To do this, one &lsquo;master&rsquo;
machine runs DCP-o-matic, and the &lsquo;server&rsquo; machines run
a small program called <code>dcpomatic_server</code>.
</para>

<para>
The master and server machines do not need to be the same type, so you
can mix Windows PCs, Macs and Linux machines as you wish.
</para>

<section>
<title>Running the servers</title>

<para>
There are two options for the encoding server;
<code>dcpomatic_server_cli</code>, which runs on the command line, and
<code>dcpomatic_server</code>, which has a simple GUI.  The command line
version is well-suited to headless servers, especially on Linux, and
the GUI version works best on Windows where it will put an icon in the
system tray.
</para>

<para>
To run the command line version, simply enter:
</para>

<programlisting>
dcpomatic_server_cli
</programlisting>

<para>
at a command prompt.  If you are running the program on a machine with
a multi-core processor, you can run multiple parallel encoding threads
by doing something like:
</para>

<programlisting>
dcpomatic_server_cli -t 4
</programlisting>

<para>
to run 4 threads in parallel.
</para>

<para>
To run the GUI version on windows, run the &lsquo;DCP-o-matic encode
server&rsquo; from the start menu.  An icon will appear in the system
tray; right-click it to open a menu from whence you can quit the
server or open a window to show its status.
</para>

<para>If you would rather not bother installing DCP-o-matic on your
server computers, the other option is to use the live-CD
image that you can download from the <ulink
url="http://dcpomatic.com/">DCP-o-matic web site.</ulink></para>

<para>Either burn the image to CD, or write it to a USB stick (using
something like <ulink
url="http://unetbootin.sourceforge.net/">unetbootin</ulink>).  Boot a
PC from the CD or USB stick and it becomes a DCP-o-matic server
without touching your standard operating system install.
</para>

</section>
<section>
<title>Setting up DCP-o-matic</title>

<para>
DCP-o-matic periodically looks on the local network for servers.  Any
that it finds are given work to do during encodes.  Selecting
<guilabel>Encoding Servers</guilabel> from the
<guilabel>Tools</guilabel> menu brings up a window which shows that
servers that DCP-o-matic has found.
</para>

</section>
<section>
<title>Some notes about encode servers</title>

<para>
DCP-o-matic does not mind if servers come and go; if a server
disappears, DCP-o-matic will stop sending work to it, and will check
it every minute or so in case it has come back online.
</para>

<para>
You will probably find that using a 1Gb/s or faster network will
provide a significant speed-up compared to a 100Mb/s network.
</para>

</section>

</chapter>

<chapter xml:id="ch-files" xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en">
<title>Generated files</title>

<para>
DCP-o-matic generates a number of files as it makes a DCP.  <xref
linkend="fig-file-structure"/> shows the files that might be generated
after you have created a DCP for a film called &lsquo;DCP Test&rsquo;.
</para>

<figure id="fig-file-structure"> 
  <title>Creating a new film</title> 
  <mediaobject>
    <imageobject> 
      <imagedata fileref="diagrams/file-structure&dia;"/>
    </imageobject> 
  </mediaobject>
</figure>

<para>
The <code>DCP Test</code> folder is the one that you specify when you
select the <guilabel>New Film</guilabel> option from DCP-o-matic's
menu.  Everything is stored inside this folder.
</para>

<para>
DCP-o-matic generates some working files as it goes along.  These are as follows:
<itemizedlist>

<listitem><code>log</code> is a list of notes that DCP-o-matic makes as it goes
along.  This can be useful for debugging purposes if something goes
wrong.</listitem>

<listitem><code>metadata</code> stores the settings that you have made
for this film: things like cropping, output format and so on.</listitem>

<listitem><code>video</code> is where DCP-o-matic writes the DCP's
video data as it encodes it.</listitem>

<listitem><code>analysis</code> is used to keep the results of audio analysis runs.</listitem>

<listitem><code>info</code> contains details of each video frame that
DCP-o-matic has written so far.  This is used when an encoding
operation is interrupted and DCP-o-matic must resume it.</listitem>
</itemizedlist>
</para>

<para>
Following this is the DCP itself:
<code>DCP-TEST_EN-XX_UK-U_51_2K_CSY_20130218_CSY_OV</code>.  This
contains some small XML files, which describe the DCP, and two large
MXF files, which contain the DCP's audio and video data.  This folder
(<code>DCP-TEST_EN-XX_...</code>) is what you should ingest, or pass
to the cinema which is showing your DCP.
</para>

</chapter>

<chapter>
<title>Loose ends</title>

<para>
This chapter collects a few notes on bits of DCP-o-matic that do not fit elsewhere in the manual.
</para>

<section>
<title>Resuming encodes</title>

<para>
If you cancel a DCP encoding run half-way through, or your computer
crashes... fear not.  DCP-o-matic takes care to ensure that, in most
cases, it can resume encoding from where it left off.  When you
re-start a DCP creation, using the same settings are a previous run,
DCP-o-matic will first check that the existing picture frames are
correct, and then resume from where it left off.  The checking of
existing frames does take some time, but it is much faster than
running a full re-encode.
</para>

<para>
This resumption is achieved by writing a digest (hash) to disk for
every image frame that is written.  On resumption, the existing MXF
file for image data is read and its contents checked against the
hashes.
</para>

</section>

</chapter>

</book>