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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Communication</title><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="index.html" title="GStreamer Application Development Manual (1.8.0)"><link rel="up" href="chapter-intro-basics.html" title="Chapter 3. Foundations"><link rel="prev" href="section-intro-basics-bins.html" title="Bins and pipelines"><link rel="next" href="part-building.html" title="Part II. Building an Application"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Communication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="section-intro-basics-bins.html">Prev</a> </td><th width="60%" align="center">Chapter 3. Foundations</th><td width="20%" align="right"> <a accesskey="n" href="part-building.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="section-intro-basics-communication"></a>Communication</h2></div></div></div><p>
<span class="application">GStreamer</span> provides several mechanisms for communication and data exchange
between the <span class="emphasis"><em>application</em></span> and the <span class="emphasis"><em>pipeline</em></span>.
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
<span class="emphasis"><em>buffers</em></span> are objects for passing streaming data
between elements in the pipeline. Buffers always travel from sources
to sinks (downstream).
</p></li><li class="listitem"><p>
<span class="emphasis"><em>events</em></span> are objects sent between elements or from
the application to elements. Events can travel upstream and downstream.
Downstream events can be synchronised to the data flow.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>messages</em></span> are objects posted by elements on
the pipeline's message bus, where they will be held for collection
by the application. Messages can be intercepted synchronously from
the streaming thread context of the element posting the message, but
are usually handled asynchronously by the application from the
application's main thread. Messages are used to transmit information
such as errors, tags, state changes, buffering state, redirects etc.
from elements to the application in a thread-safe way.
</p></li><li class="listitem"><p>
<span class="emphasis"><em>queries</em></span> allow applications to request information
such as duration or current playback position from the pipeline.
Queries are always answered synchronously. Elements can also use
queries to request information from their peer elements (such as the
file size or duration). They can be used both ways within a pipeline,
but upstream queries are more common.
</p></li></ul></div><div class="figure-float" style="float: left;"><div class="figure"><a name="section-communication-img"></a><p class="title"><b>Figure 3.2. <span class="application">GStreamer</span> pipeline with different communication flows</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/communication.png" width="405" alt="GStreamer pipeline with different communication flows"></div></div></div><br class="figure-break"></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="section-intro-basics-bins.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="chapter-intro-basics.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="part-building.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Bins and pipelines </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Part II. Building an Application</td></tr></table></div></body></html>
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