+When content channels are copied into DCP channels they can be done
+with variable gain. If, for example, you want to copy a channel
+as-is, you can set a gain of 0dB. Alternatively, if you want to mix
+two channels into one, you may want to use a gain of -6dB on each one
+to prevent clipping when the two channels are added.
+</para>
+
+<para>
+The green boxes of the audio mapping view tell you (very roughly) how
+much gain is applied to each channel. A full-height box means 0dB
+(i.e. unity) gain. Any less height indicates lower gain.
+</para>
+
+<para>
+To map one channel to another with 0dB gain, click in the empty box
+and it will turn green to reflect the mapping. A second click will
+turn the mapping back off. To set some other gain, right-click on the
+box to open the gain menu. This allows you to set
+<guilabel>Off</guilabel> (no mapping or negative infinity gain),
+<guilabel>Full</guilabel> (0dB gain), -6dB gain or
+<guilabel>Edit</guilabel> which allows you to set the required gain
+precisely.
+</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. The full green boxes show that the
+mapping is at unity gain (0dB) in each case. Imagine that we modify
+the settings to those shown 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. The smaller
+green boxes on the centre mappings show that those channels are added
+with some non-unity gain; you can see by hovering the mouse pointer
+over those boxes that the gain for content channels 1 and 2 is -6dB
+when being sent to the centre channel and 0dB when being sent to left
+and right.
+</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>
+The <guilabel>Use this DCP's audio as OV and make VF</guilabel>
+checkbox is only applicable if the selected content is an existing
+DCP. It allows you to make a VF DCP, using the audio content from the
+existing DCP by referencing it (rather than copying). See <xref
+linkend="sec-overlay"/>.
+</para>
+
+<para>
+<guilabel>Show graphs of audio levels</guilabel> will analyse the
+audio of the selected content and plot it on a graph. See <xref
+linkend="sec-show-audio"/> for more details.
+</para>
+
+<para>
+‘Audio Gain’ 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>
+
+</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 can either:
+</para>
+
+<itemizedlist>
+ <listitem>Extract subtitles that are embedded in video files, or</listitem>
+ <listitem>Use subtitles from SubRip (<code>.srt</code>), SubStation
+ Alpha (<code>.ssa</code> or <code>.ass</code>) or DCP XML files. You may find the great
+ free program <ulink
+ url="http://www.nikse.dk/subtitleedit/">Subtitle Edit</ulink> useful
+ for creating such files.</listitem>
+</itemizedlist>
+
+<para>
+Embedded subtitles are usually represented using a set of bitmaps,
+especially on files that have come from DVD or BluRay. Such subtitles
+can (currently) only be ‘burnt’ into the DCP (that is,
+they are included in the image and not overlaid by the projector).
+</para>
+
+<para>
+With SubRip, SubStation Alpha or DCP subtitles you have the choice to
+either burn-in or include the subtitles as separate subtitle
+‘asset’ within your DCP (in which case the projector
+overlays them onto the image on playback). The difference between
+burn-in and overlay is illustrated by <xref linkend="fig-burn-in"/>
+and <xref linkend="fig-discrete"/>.
+</para>
+
+<figure id="fig-burn-in">
+ <title>Burnt-in subtitles</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/burn-in&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<figure id="fig-discrete">
+ <title>Separate subtitles</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/discrete&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+The advantage of separate subtitles is that the same video content can
+be used for DCPs in many different languages. This means that only a
+small text file needs to be changed for each target language, rather
+than a large video file. It also means that the time-consuming video
+encoding need only be done once for the project rather than once for
+every language.
+</para>
+
+<para>
+Select the <guilabel>Use Subtitles</guilabel> check-box to enable
+the subtitles in the selected content.
+</para>
+
+<para>
+Select the <guilabel>Burn subtitles into image</guilabel> check-box to
+burn these subtitles into the image; if this is not ticked the
+subtitles will be included separately in the DCP to be rendered by the
+projector. This check-box will always be ticked if you are using
+embedded ‘image’ subtitles.
+</para>
+
+<para>
+The <guilabel>X Offset</guilabel> and <guilabel>Y Offset</guilabel>
+controls move the subtitles around within the image. The offsets are
+expressed as a percentage of the video frame size; 100% X offset is
+the entire width of the frame, and 100% Y offset is the entire height.
+Hence, to move the subtitles down by half the frame height you would
+use a Y offset of 50%.
+</para>
+
+<para>
+The <guilabel>X Scale</guilabel> and <guilabel>Y Scale</guilabel>
+controls scale the subtitles. Scale values of 1 make the subtitles
+the same size (relative to the size of the image) as they are on the
+original. Values lower than 1 make them smaller, and values higher
+make them larger. You can stretch the subtitles in either direction
+by specifying different values for X and Y scale. Subtitles from DVD
+and Blu Ray sources are frequently larger (relative to the video
+frame) than those typically used for DCP, so it is often useful to
+scale such subtitles down using these controls.
+</para>
+
+<para>
+The <guilabel>Line spacing</guilabel> control adjusts the line spacing
+of the subtitles. This only works for non-embedded (text) subtitles.
+</para>
+
+<para>
+The <guilabel>Stream</guilabel> control changes the subtitle stream
+that is used when the content has more than one.
+</para>
+
+<para>
+If you are using non-embedded (text) subtitles you can see the
+subtitle text and timings by clicking the <guilabel>View...</guilabel>
+button, or specify the fonts that should be used by clicking <guilabel>Fonts...</guilabel>.
+</para>
+
+<para>
+With any subtitles you can click <guilabel>Appearance...</guilabel> to
+change how the subtitles look.
+</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 scale="100" 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. You can set this amount to
+trim up to the current preview position by clicking <guilabel>Trim up
+to current position</guilabel>.
+</para>
+
+<para>
+<guilabel>Trim from end</guilabel> specifies the amount that should be
+trimmed from the end of the content. You can set this amount to trim
+after the current preview position by clicking <guilabel>Trim after to
+current position</guilabel>.
+</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. It can also be used to override the detected
+frame rate of other content if DCP-o-matic has got it wrong.
+</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>
+
+
+<!-- ============================================================== -->
+<section>
+<title>Video processing pipeline</title>
+
+<para>
+This section gives a little more detail about how DCP-o-matic process
+video as it takes it from a source and puts it into a DCP.
+</para>
+
+<para>
+Consider, as a somewhat over-the-top example, that we have a 720 x 576
+image which is letterboxed with 36 black pixels each at the top and
+bottom, and the video content within the letterbox should be presented
+in the DCP at ratio of 2.39:1 within a 1.85:1 frame (such as might
+happen with a trailer). The source image is shown in <xref
+linkend="fig-pipeline1"/>.
+</para>
+
+<figure id="fig-pipeline1">
+ <title>Example image to demonstrate video processing</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/pipeline1&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+DCP-o-matic runs through the following steps when preparing an image for a DCP:
+</para>
+
+<itemizedlist>
+<listitem>Crop</listitem>
+<listitem>Scale</listitem>
+<listitem>Place in container</listitem>
+</itemizedlist>
+
+<para>
+First, some amount of the image can be cropped. This is almost always
+used to remove black borders (letterboxing and/or pillarboxing) around
+images.
+</para>
+
+<para>
+In our example image, we would use 36 pixels of crop from the top and
+bottom. This would give the new image shown in <xref
+linkend="fig-pipeline2"/>.
+</para>
+
+<figure id="fig-pipeline2">
+ <title>Example image after cropping</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/pipeline2&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+The next step is to scale the image. Since this content should be
+presented in a 2.39:1 aspect ratio inside a 1.85:1 DCP we would select
+<guilabel>Scope</guilabel> from the <guilabel>Scale to</guilabel>
+option in the <guilabel>Video</guilabel> tab and
+<guilabel>Flat</guilabel> from the <guilabel>Container</guilabel>
+option in the <guilabel>DCP</guilabel> tab.
+</para>
+
+<para>The <guilabel>Scale to</guilabel> option should always be set to
+the aspect ratio at which the content should be seen. The
+<guilabel>Container</guilabel> option should be set to the preset that
+you want to use on the projector. Of course, these two settings will
+often be the same.
+</para>
+
+<para>
+Given the scaling and container information, DCP-o-matic will look at
+the DCP's container size, and then scale the source image up until one
+or both of its dimensions (width, height or both) fits the size of the
+container, all the while preserving the desired aspect ratio.
+</para>
+
+<para>
+In our example here, the DCP's container is specified as 1.85:1 (so
+that the DCP will play back correctly using the projector's
+‘Flat’ preset). At 2K, 1.85:1 is 1998 pixels by 1080.
+Scaling the source up whilst preserving its 1.85:1 aspect ratio will
+result in the image hitting the sides of the container first, at a
+size of 1998 x 836. This gives us a new version of the image as shown
+in <xref linkend="fig-pipeline3"/>.
+</para>
+
+<figure id="fig-pipeline3">
+ <title>Example image after cropping and scaling</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/pipeline3&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<para>
+The final step is to place the image into the DCP. In this case,
+since we have a 2.39:1 image that should be presented as a 1.85:1 DCP,
+we have set the <guilabel>container</guilabel> in the
+<guilabel>DCP</guilabel> tab to be Scope. Since the content has been
+scaled to 1998 x 836, and a Flat container is 1998 x 1080, there will
+be some black bars at the top and bottom of the image. DCP-o-matic
+shares out this black equally, as shown in <xref
+linkend="fig-pipeline3"/>.
+</para>
+
+<figure id="fig-pipeline4">
+ <title>Example image in the DCP</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="100" fileref="diagrams/pipeline4&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+</section>
+
+
+<section>
+ <title>Copy and paste settings</title>
+
+<para>
+Once you have set up a piece of content it is possible to copy the
+settings you have applied to another piece of content. To do this,
+select the content to copy from and choose <guilabel>Copy</guilabel>
+from the <guilabel>Edit</guilabel> menu. Then select the content to
+copy to and choose <guilabel>Paste</guilabel>. A dialogue box will
+open to allow you to choose which settings you want to copy. Clicking
+<guilabel>OK</guilabel> will apply the copied settings.
+</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 you want to take the ISDCF-compliant name that DCP-o-matic
+generates and modify it, click <guilabel>Copy as name</guilabel> and
+the ISDCF name will be copied into the <guilabel>Name</guilabel> box.
+You can then edit it as you wish. The DCP name should not matter (in
+that it should not affect how the DCP ingests or plays) but
+projectionists will appreciate it if you use the standard naming
+scheme as it makes it easier to identify details of the content.
+</para>
+
+<para>
+The <guilabel>Content Type</guilabel> option can be
+‘feature’, ‘trailer’ or whatever; select the
+required type from the drop-down list. On some projection systems
+this will affect where your content appears in the projector's server
+user interface, so take care to select an appropriate type.
+</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>
+If you use encryption DCP-o-matic will generate a random encryption
+key for you. To specify your own key, click the
+<guilabel>Edit..</guilabel> button next to the key.
+</para>
+
+<para>
+The <guilabel>Reels</guilabel> and <guilabel>Reel length</guilabel>
+controls specify how the DCP will be split up into
+‘reels’. See <xref linkend="sec-reels"/> below.
+</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>
+Ticking the <guilabel>Upload DCP to TMS after it is made</guilabel>
+will ask DCP-o-matic to copy the finished DCP to your configured TMS (see <xref linkend="sec-prefs-tms"/>).
+</para>
+
+<para>
+At the bottom of the DCP tab are a further two tabs, one each to
+contain the settings for the DCP's video and audio parts.
+</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>
+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>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>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).
+Most commercial DCPs use bit rates between 75 and 125 MBit/s.
+</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.
+You can only set an even number of channels here, since that is
+required by the DCI standard. If you want an odd number of channels,
+set the DCP channel count to one greater than you need and the
+unused channel will be filled with silence.
+</para>
+
+<para>
+The <guilabel>Processor</guilabel> control allows you to select a
+process to apply to the audio before it goes into the DCP. Three processes are currently provided:
+</para>
+
+<itemizedlist>
+<listitem>Mid-side decode — this will take a L/R
+stereo input and extract the common part (corresponding to the
+‘Mid’ in a mid-side signal) into the DCP's centre channel.
+The remaining L/R parts will be kept in the L/R channels of the DCP.
+This may be useful to make near-field L/R mixes more compatible with
+cinema audio systems.</listitem>
+<listitem>Stereo to 5.1 up-mixer A — this will take a stereo input and up-mix it to ‘fake’ 5.1. The input L/R are treated as follows:
+<itemizedlist>
+<listitem>DCP L is input L bandpass-filtered between 1.9kHz and 4.8kHz.</listitem>
+<listitem>DCP R is input R bandpass-filtered between 1.9kHz and 4.8kHz.</listitem>
+<listitem>DCP C is input L mixed with input R, taken down by 3dB and then bandpass-filtered between 150Hz and 1.9kHz.</listitem>
+<listitem>DCP Lfe is input L mixed with input R, taken down by 3dB and then bandpass-filtered between 20Hz and 150Hz.</listitem>
+<listitem>DCP Ls is input L bandpass-filtered between 4.8kHz and 20kHz.</listitem>
+<listitem>DCP Rs is input R bandpass-filtered between 4.8kHz and 20kHz.</listitem>
+</itemizedlist>
+<para>
+This upmixing algorithm is due to Gérald Maruccia.
+</para>
+</listitem>
+<listitem>Stereo to 5.1 up-mixer B — this uses a different approach:
+<itemizedlist>
+ <listitem>DCP L is input L.</listitem>
+ <listitem>DCP R is input R.</listitem>
+ <listitem>DCP C is input L + input R taken down by 3dB.</listitem>
+ <listitem>DCP Lfe is DCP C bandpass filtered between 20Hz and 150Hz.</listitem>
+ <listitem>DCP Ls and Rs are input L - input R with a 20ms delay.</listitem>
+</itemizedlist>
+</listitem>
+</itemizedlist>
+
+<!-- ============================================================== -->
+<section xml:id="sec-reels">
+<title>Reels</title>
+
+<para>
+A ‘reel’ in a DCP is a subsection of the DCP, in the same
+way as a 35mm reel is a section of a film. A DCP can be split up into
+any number of reels and the joins (the equivalent to 35mm splices)
+between the reels are seamless.
+</para>
+
+<para>
+There is no reason why you can't just use a single reel for the whole
+of your DCP, as there is no limit on their length. Many people choose
+to do this.
+</para>
+
+<para>
+There are, however, some possible advantages of splitting things up
+into reels:
+</para>
+
+<itemizedlist>
+<listitem>
+The picture, sound and subtitle data of the DCP will be
+split up into more smaller files on disk, rather than fewer larger
+files. This can be useful if the DCP is to be transferred on storage
+that have file size limits. The FAT32 filesystem, for example, can
+only hold files smaller than 4Gb. A 6Gb DCP with a single reel could
+not be transferred using a FAT32-formatted disk. If that DCP were
+split up into two 3Gb reels it could be transferred.
+</listitem>
+<listitem>
+It is easier to re-use DCP components if they are in reels. Consider,
+for example, a film company who wants to put a 5 second ident onto the
+beginning of DCPs that they distribute. If they receive a feature
+film DCP they can modify it to add their ident as a separate reel.
+This is easier than attaching the picture data in the DCP.
+</listitem>
+</itemizedlist>
+
+<para>
+DCP-o-matic offers three options for setting up the reels in your DCP:
+single reel, split by video content or custom.
+</para>
+
+<para>
+<guilabel>Single reel</guilabel>, as its name suggests, keeps the whole DCP as one reel.
+This is a perfectly good option if you have no particular reason to
+need reels.
+</para>
+
+<para>
+<guilabel>Split by video content</guilabel> puts each piece of source
+video content in its own reel, as shown in <xref linkend="fig-reels-by-video"/>.
+</para>
+
+<figure id="fig-reels-by-video">
+<title>Making reels using split by video content</title>
+<mediaobject><imageobject><imagedata scale="100" fileref="diagrams/reels-by-video&dia;"/></imageobject></mediaobject>
+</figure>
+
+<para>
+Here we have three video files (<code>ident.mp4</code>,
+<code>feature.ts</code> and <code>cred.mov</code>). With
+<guilabel>split by video content</guilabel> DCP-o-matic makes a new
+reel to hold each video file.
+</para>
+
+<para>
+<guilabel>Custom</guilabel> splits reels by the size of the files that
+will make up their video content. With <guilabel>Custom</guilabel>
+you must specify a reel length in Gb. Then no file in the DCP will be larger than this reel length.
+</para>
+
+</section>
+
+
+<!-- ============================================================== -->
+<section xml:id="sec-show-audio">
+<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.