+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 ‘burnt into’ 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>
+
+<section>
+<title>Timing</title>
+
+<para>
+The timing tab contains settings related to the timing of your
+content, as shown in <xref linkend="fig-timing-tab-detail"/>.
+</para>
+
+<figure id="fig-timing-tab-detail">
+ <title>Timing settings tab</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="screenshots/timing-tab&scs;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+Most of the timing tab's entries are <emphasis>time-codes</emphasis>.
+These are expressed as four numbers, as shown in <xref
+linkend="fig-timecode"/>.
+</para>
+
+<figure id="fig-timecode">
+ <title>Timecode</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="diagrams/timecode&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+<guilabel>Position</guilabel> is the time at which this piece of
+content should start within the DCP. In most cases, this will be
+<code>0:0:0:0</code> to make the content start at the beginning of the
+DCP.
+</para>
+
+<para>
+<guilabel>Full length</guilabel> is the length of the piece of
+content. This can only be set for still-image content: for video or
+sound content, it is fixed by the nature of the content file. If
+still-image content is being used you can set the length for which it
+should be displayed using this control.
+</para>
+
+<para>
+<guilabel>Trim from start</guilabel> specifies the amount that should be trimmed from the start of the content.
+</para>
+
+<para>
+<guilabel>Trim from end</guilabel> specifies the amount that should be trimmed from the end of the content.
+</para>
+
+<para>
+<guilabel>Play length</guilabel> indicates how long this piece of
+content will be once the trims have been applied. This will be equal
+to the full length minus <guilabel>trim-from-start</guilabel> and minus <guilabel>trim-from-end</guilabel>.
+</para>
+
+<para>
+<guilabel>Video frame rate</guilabel> specifies the frame rate for still-image content.
+</para>
+
+<para>
+Each timecode control has a <guilabel>Set</guilabel> which you should
+click when you have entered a new value for a timecode. The
+<guilabel>Set</guilabel> button will make DCP-o-matic take account of
+any changes to the corresponding timecode.
+</para>
+
+</section>
+
+</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 ISDCF
+name</guilabel> is not ticked, the name that you specify will be used
+as-is for the name of the DCP. If <guilabel>Use ISDCF name</guilabel>
+is ticked, the name that you enter will be used as part of a
+ISDCF-compliant name.
+</para>
+
+<para>
+Underneath the name field is a preview of the name that the DCP will
+get. To use a ISDCF-compliant name, tick the <guilabel>Use ISDCF
+name</guilabel> check-box. The ISDCF name will be composed using details
+of your content's soundtrack, the current date and other things that
+can be specified in the ISDCF 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 ‘Flat’ for the DCP.
+</para>
+
+<para>
+Next up is the content type. This can be
+‘feature’, ‘trailer’ 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>Signed</guilabel> check-box sets whether or not the DCP
+is signed. This is rarely important; if in doubt, tick it.
+</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 ‘approved’ 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.