-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>X Offset</guilabel> and <guilabel>Y
-Offset</guilabel> controls move the subtitles around within the image,
-and the <guilabel>scale</guilabel> control changes their size. The
-<guilabel>Stream</guilabel> control changes the subtitle stream that
-is used when the content has more than one.
+included in the image and not overlaid by the projector) or included
+as a separate subtitle ‘asset’ within your DCP (in which
+case the projector overlays them onto the image on playback). The
+difference between these two arrangements 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="80" fileref="diagrams/burn-in&dia;"/>
+ </imageobject>
+ </mediaobject>
+</figure>
+
+<figure id="fig-discrete">
+ <title>Separate subtitles</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata scale="80" 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>
+Note that subtitles come in two types: text and bitmap. Text
+subtitles are expressed as plain text and can be either burnt into the
+image or included as a separate subtitle asset within the DCP. Bitmap
+subtitles, on the other hand, are expressed as pre-rendered bitmaps.
+They cannot (yet) be added to the DCP as a separate asset and must be
+burnt into the image.
+</para>
+
+<para>
+Select the <guilabel>Use Subtitles</guilabel> check-box to enable
+these subtitles.
+</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.
+</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.