gstreamer/docs/libs/architecture.xml

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<refentry id="ges-architecture" revision="25 mar 2009">
  <refmeta>
    <refentrytitle>Overview and architecture</refentrytitle>

    <manvolnum>1</manvolnum>

    <refmiscinfo>GStreamer Editing Services</refmiscinfo>
  </refmeta>

  <!-- <refnamediv> -->

  <!-- <refname>Overview</refname> -->

  <!-- <refpurpose> -->

  <!-- Goals of the GStreamer Editing Services. -->

  <!-- </refpurpose> -->

  <!-- </refnamediv> -->

  <refsect1>
    <title>Goals of GStreamer Editing Services</title>

    <para>The GStreamer multimedia framework and the accompanying GNonLin set
    of plugins for non-linear editing offer all the building blocks for:
    <itemizedlist>
        <listitem>
          <para>Decoding and encoding to a wide variety of formats, through
          all the available GStreamer plugins.</para>
        </listitem>

        <listitem>
          <para>Easily choosing segments of streams and arranging them through
          time through the GNonLin set of plugins.</para>
        </listitem>
      </itemizedlist></para>

    <para>But all those building blocks only offer stream-level access, which
    results in developers who want to write non-linear editors to write a
    consequent amount of code to get to the level of <emphasis>non-linear
    editing</emphasis> notions which are closer and more meaningful for the
    end-user (and therefore the application).</para>

    <para>The GStreamer Editing Services <remark>(hereafter GES)</remark> aims
    to fill the gap between GStreamer/GNonLin and the application developer by
    offering a series of classes to simplify the creation of many kind of
    editing-related applications.</para>
  </refsect1>

  <refsect1>
    <title>Architecture</title>

    <refsect2>
      <title>Timeline and TimelinePipeline</title>

      <para>The most top-level object encapsulating every other object is the
      <link linkend="GESTimeline">GESTimeline</link>. It is the central object
      for any editing project.</para>

      <para>The <classname>GESTimeline</classname> is a
      <classname>GstElement</classname>. It can therefore be used in any
      GStreamer pipeline like any other object.</para>

      <para>The GESTimeline can contain two types of objects (seen in <xref
      linkend="layer_tracks_diagram" />): <itemizedlist>
          <listitem>
            <para>Layers - Corresponds to the user-visible layout of
            non-overlapping objects. A minimalistic timeline would only have
            one layer. A more complex editing application could use as many as
            needed.</para>
          </listitem>

          <listitem>
            <para>Tracks - Corresponds to the output stream formats. A typical
            GESTimeline would have a audio track and a video track. An audio
            editor would only require one single audio Track.</para>
          </listitem>
        </itemizedlist></para>

      <figure float="0" id="layer_tracks_diagram">
        <title>Layers and Tracks</title>

        <mediaobject>
          <imageobject>
            <imagedata fileref="layer_track_overview.png" scale="75" />
          </imageobject>
        </mediaobject>
      </figure>

      <para>In order to reduce even more the amount of GStreamer interaction
      the application developer has to deal with , a convenience GstPipeline
      has been made available specifically for Timelines : <link
      linkend="GESTimelinePipeline">GESTimelinePipeline</link>.</para>
    </refsect2>

    <refsect2>
      <title>Timeline layers</title>

      <para>The layers are the end-user visible part of GES.</para>
    </refsect2>

    <refsect2>
      <title>Timeline Tracks</title>

      <para>The tracks are the GStreamer-level components of a Timeline. They
      are a 1-to-1 relationship to the output streams.</para>
    </refsect2>
  </refsect1>
</refentry>