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Original commit message from CVS: First draft of Chapter 1 (introduction) and Chapter 2 (basic concepts) of the GStreamer manual.
95 lines
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Text
95 lines
4 KiB
Text
<chapter id="cha-elements">
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<title>GstElement</title>
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<para>
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The most important object in GStreamer for the application programmer is
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the GstElement object.
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</para>
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<sect1 id="sec-elements-design">
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<title>What is a GstElement</title>
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<para>
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The GstElement is the basic building block for the media pipeline. All the
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different components you are going to use are derived from this GstElement.
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This means that a lot of functions you are going to use operate on this object.
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</para>
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<para>
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We will first describe the three most important types of elements that you are
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going to use. They are the Source, Filter and Sink elements.
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</para>
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<para>
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You will also see that those elements have pads. These are the elements
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connections with the 'outside' world.
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</para>
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<sect2 id="sec-elements-src">
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<title>GStreamer source elements (<classname>GstSrc</classname>)</title>
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<para>
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This element will generate data that will be used by the pipeline. It is
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typically a file or an audio source.
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</para>
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<para>
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Below you see how we will visualize the <classname>GstSrc</classname> element.
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We always draw a src pad to the right of the element.
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</para>
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<figure float="1" id="sec-element-srcimg">
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<title>Visualisation of a <classname>GstSrc</classname> element</title>
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<graphic fileref="images/src-element" format="png"></graphic>
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</figure>
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<para>
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Source elements do not accept data, they only generate data. You can see
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this in the figure because it only has a src pad. A src pad can only
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generate buffers.
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</para>
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</sect2>
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<sect2 id="sec-elements-filter">
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<title>GStreamer filter elements (<classname>GstFilter</classname>)</title>
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<para>
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Filter elements both have an input and an output pad. They operate on data
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they receive in the sink pad and send the result to the src pad.
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</para>
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<para>
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Examples of a filter element might include: an MPEG decoder, volume filter,...
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</para>
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<para>
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Filters may also contain any number of input pads and output pads. For example,
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a video mixer might have to input pads (the images of the two different video
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streams) and one output pad.
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</para>
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<figure float="1" id="sec-element-filterimg">
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<title>Visualisation of a <classname>GstFilter</classname> element</title>
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<graphic fileref="images/filter-element" format="png"></graphic>
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</figure>
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<para>
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The above figure shows the visualisation of a filter element. This element has
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one sink pad (input) and one src (output) pad. Sink pads are drawn on the left
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of the element.
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</para>
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<figure float="1" id="sec-element-multifilterimg">
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<title>Visualisation of a <classname>GstFilter</classname> element with
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more than one output pad</title>
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<graphic fileref="images/filter-element-multi" format="png"></graphic>
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</figure>
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<para>
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The above figure shows the visualisation of a filter element with more than one
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output pad. An example of such a filter is the AVI splitter. This element will
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parse the input data and extracts the audio and video data. Most of these filters
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dynamically send out a signal when a new pad is created so that the application
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programmer can connect an arbitrary element to the newly created pad.
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</para>
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</sect2>
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<sect2 id="sec-elements-sink">
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<title>GStreamer sink elements (<classname>GstSink</classname>)</title>
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<para>
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This element accepts data but will not generate any new data. A sink element
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is typically a file on disk, a soundcard, a display,... It is presented as
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below:
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</para>
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<figure float="1" id="sec-element-sinkimg">
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<title>Visualisation of a <classname>GstSink</classname> element</title>
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<graphic fileref="images/sink-element" format="png"></graphic>
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</figure>
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</sect2>
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</sect1>
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</chapter>
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