Latest revision as of 15:15, 11 May 2015

The osd_subtitle.xml file governs the formatting of the font and background for text-based subtitles and captions. Two common uses are to change the font and to customize the background, such as using no background or a translucent background. This applies to text, teletext, CEA-608, and CEA-708 captions.

Basics

Definitions must appear within the osd_subtitle window. The only relevant MythUI objects are fontdef (for the text font attributes) and shape (for the background attributes). The name of each fontdef and shape corresponds to the subtitle type. Each fontdef and shape should ultimately inherit from a special object named "provider", which represents the default formatting of a particular subtitle, and the fontdef or shape can override any of the provider attributes with custom values.

All elements and attributes of fontdef and shape are supported, except that the area and size elements are explicitly ignored, as they are determined by the subtitle drawing code.

Subtitle types

Example

The following example forces .srt subtitles to be rendered in yellow text, FreeSans font, black shadow, with a translucent black background. The fontdef and shape names are "text" since the subtitles come from a .srt file. Note that in this example, color formatting controls in the .srt file will be ignored due to the explicit setting of yellow text.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE mythuitheme SYSTEM "http://www.mythtv.org/schema/mythuitheme.dtd">
<mythuitheme>
  <window name="osd_subtitle">
    <fontdef name="text" face="FreeSans" from="provider">
      <color>#FFFF00</color>
      <shadowoffset>2,2</shadowoffset>
      <shadowcolor>#000000</shadowcolor>
    </fontdef>
    <shape name="text" from="provider">
      <fill color="#000000" alpha="100" />
    </shape>
  </window>
</mythuitheme>

Reference implementation

The themes/default/osd_subtitle.xml file contains a "reference implementation" that explicitly describes the implicit defaults for the various subtitle types in the case that the theme does not provide any specification. As such, these definitions are redundant, but they are provided as documentation and as a template for the theme writer to extend.

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE mythuitheme SYSTEM "http://www.mythtv.org/schema/mythuitheme.dtd">
<mythuitheme>
    <window name="osd_subtitle">
        <!--
            This is a reference implementation of the system/provider
            defaults specified in
            SubtitleFormat:CreateProviderDefault().

            Note that if all attributes/elements are simply inherited
            from provider, then the specification is optional.  E.g.,
            the following could be omitted:

            <fontdef name="sample" from="provider"></fontdef>
            <shape   name="sample" from="provider"></shape>

            Also note that these specific definitions are unnecessary
            since they are the same as the defaults in the code.  A
            theme only needs to include the definitions that it wants
            to change/override.
          -->

        <shape name="black_background" from="provider">
          <type>box</type>
          <fill color="#000000" alpha="255" />
          <line color="#000000" alpha="255" width="0" />
        </shape>


        <!--
            Subtitle type "text" generally comes from external text
            files like .srt or .txt files.
           -->
        <fontdef name="text" face="Droid Sans" from="provider">
        </fontdef>

        <shape   name="text" from="black_background">
        </shape>


        <!--
            Digital teletext text-based subtitles.  Not to be confused
            with bitmap teletext subtitles, or CEA-608 teletext
            captions.  A monospaced font should be used.
           -->
        <fontdef name="teletext" face="FreeMono" from="provider">
        </fontdef>

	<!--
	    This allows overriding the alpha (transparency) value of
	    non-transparent subtitles.  Note that the parser requires
	    some color to be specified here, but it will be ignored
	    and the provider's value will be used instead.
	   -->
        <shape   name="teletext" from="provider">
          <fill color="#000000" alpha="255" />
        </shape>


        <!--
            CEA-608 closed captions.  These also apply to CEA-608 VBI
            teletext captions.  A monospaced font should be used.
           -->
        <fontdef name="608" face="FreeMono" from="provider">
        </fontdef>

        <shape   name="608" from="black_background">
        </shape>


        <!--
            CEA-708 closed captions.  The spec defines 8 different
            font tags, but in practice (at least in the U.S.), only
            tags 0 and 3 are used by broadcasters.
           -->
        <!-- Font tag 0: "Default" -->
        <fontdef name="708_0" face="FreeMono"        from="provider">
        </fontdef>

        <!-- Font tag 1: "Monospaced Serif" -->
        <fontdef name="708_1" face="FreeMono"        from="provider">
        </fontdef>

        <!-- Font tag 2: "Proportional Serif" -->
        <fontdef name="708_2" face="Droid Serif"     from="provider">
        </fontdef>

        <!-- Font tag 3: "Monospaced Sans Serif" -->
        <fontdef name="708_3" face="Droid Sans Mono" from="provider">
        </fontdef>

        <!-- Font tag 4: "Proportional Sans Serif" -->
        <fontdef name="708_4" face="Droid Sans"      from="provider">
        </fontdef>

        <!-- Font tag 5: "Casual" -->
        <fontdef name="708_5" face="Purisa"          from="provider">
        </fontdef>

        <!-- Font tag 6: "Cursive" -->
        <fontdef name="708_6" face="TeX Gyre Chorus" from="provider">
        </fontdef>

        <!-- Font tag 7: "Small Capitals" -->
	<!-- Note: The Qt property QFont::SmallCaps is automatically
	     applied to this font. -->
        <fontdef name="708_7" face="Droid Serif"     from="provider">
        </fontdef>

    </window>
</mythuitheme>