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><H1
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><A
NAME="section-elements-types"
>4.2. Types of elements</A
></H1
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="section-elements-src"
>4.2.1. Source elements</A
></H2
><P
> Source elements generate data for use by a pipeline, for example
reading from disk or from a sound card.
</P
><P
> <A
HREF="section-elements-types.html#section-element-srcimg"
>Figure 4-1</A
> shows how we will visualise
a source element.
We always draw a source pad to the right of the element.
</P
><DIV
CLASS="figure"
><A
NAME="section-element-srcimg"
></A
><P
><B
>Figure 4-1. Visualisation of a source element</B
></P
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="images/src-element.png"></P
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><P
> Source elements do not accept data, they only generate data. You can
see this in the figure because it only has a source pad. A source
pad can only generate data.
</P
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CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="section-elements-filter"
>4.2.2. Filters and codecs</A
></H2
><P
> Filter elements have both input and output pads. They operate on
data they receive in their sink pads and produce data on their source
pads. For example, MPEG decoders and volume filters would fall into
this category.
</P
><P
> Elements are not constrained as to the number of pads they might have;
for example, a video mixer might have two input pads (the images of
the two different video streams) and one output pad.
</P
><DIV
CLASS="figure"
><A
NAME="section-element-filterimg"
></A
><P
><B
>Figure 4-2. Visualisation of a filter element</B
></P
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="images/filter-element.png"></P
></DIV
></DIV
><P
> <A
HREF="section-elements-types.html#section-element-filterimg"
>Figure 4-2</A
> shows how we will visualise
a filter element.
This element has one sink (input) pad and one source (output) pad.
Sink pads are drawn on the left of the element.
</P
><DIV
CLASS="figure"
><A
NAME="section-element-multifilterimg"
></A
><P
><B
>Figure 4-3. Visualisation of a filter element with
more than one output pad</B
></P
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="images/filter-element-multi.png"></P
></DIV
></DIV
><P
> <A
HREF="section-elements-types.html#section-element-filterimg"
>Figure 4-2</A
> shows the visualisation of a filter element with
more than one output pad. An example of such a filter is the AVI
demultiplexer. This element will parse the input data and
extract the audio and video data. Most of these filters dynamically
send out a signal when a new pad is created so that the application
programmer can link an arbitrary element to the newly created pad.
</P
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><H2
CLASS="sect2"
><A
NAME="section-elements-sink"
>4.2.3. Sink elements</A
></H2
><P
> Sink elements are end points in a media pipeline. They accept
data but do not produce anything. Disk writing, soundcard playback,
and video output would all be implemented by sink elements.
<A
HREF="section-elements-types.html#section-element-sinkimg"
>Figure 4-4</A
> shows a sink element.
</P
><DIV
CLASS="figure"
><A
NAME="section-element-sinkimg"
></A
><P
><B
>Figure 4-4. Visualisation of a sink element</B
></P
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><IMG
SRC="images/sink-element.png"></P
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