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332 lines
11 KiB
XML
332 lines
11 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY % local.common.attrib "xml:base CDATA #IMPLIED">
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<!ENTITY % ents SYSTEM "gst-python.ent">
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%ents;
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]>
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<article id="gst-python">
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<articleinfo>
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<title>Gst-Python &version;: A Python Interface to GStreamer</title>
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<publisher><publishername>The GStreamer Development Team</publishername></publisher>
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<pubdate>&pubdate;</pubdate>
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<copyright><year>2003</year><holder>David I. Lehn</holder></copyright>
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<titleabbrev>gst-python</titleabbrev>
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<authorgroup>
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<author>
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<firstname>David</firstname>
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<othername role="mi">I.</othername>
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<surname>Lehn</surname>
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<email>dlehn@users.sourceforge.net</email>
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</author>
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</authorgroup>
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<abstract>
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<para>Introductory information for the GStreamer Python bindings.</para>
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<para><ulink url="http://gstreamer.freedesktop.org/bindings/python.html"/></para>
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</abstract>
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<revhistory>
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<revision>
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<revnumber>0.1.0</revnumber>
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<date>2003-07-10</date>
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<authorinitials>dil</authorinitials>
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<revremark>Initial version.</revremark>
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</revision>
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</revhistory>
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</articleinfo>
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<!--=====================================================================-->
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<section id="about">
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<title>About</title>
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<para>
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<application>gst-python</application>: the <ulink url="http://www.python.org/">Python</ulink> bindings for the <ulink url="http://www.gstreamer.net/">GStreamer</ulink> project. These bindings provide access to almost all of the GStreamer C API through an object oriented Python API.
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</para>
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</section>
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<!--=====================================================================-->
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<xi:include href="NEWS.xml#news" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<!--=====================================================================-->
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<section id="installation">
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<title>Installation</title>
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<!--=================-->
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<section id="requirements">
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<title>Requirements</title>
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<itemizedlist>
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<listitem><para>
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Python 2.2 (<ulink url="http://www.python.org/"/>)
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</para></listitem>
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<listitem><para>
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GStreamer 0.6.x (<emphasis>except</emphasis> 0.6.1) (<ulink url="http://www.gstreamer.net/"/>)
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</para></listitem>
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<listitem><para>
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PyGTK 1.99.14 (<ulink url="http://www.daa.com.au/~james/pygtk/"/>)
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</para></listitem>
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</itemizedlist>
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</section>
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<!--=================-->
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<section id="building">
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<title>Building and Installation</title>
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<para>
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For build and install information please refer to the "INSTALL" file. Installation is optional, gst-python can be used from the build directory. The quick instructions: build and install PyGTK and GStreamer then build gst-python:
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</para>
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<para>
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<screen>
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$ ./configure && make
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</screen>
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</para>
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</section>
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<!--=================-->
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<section id="using">
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<title>Using</title>
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<para>
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You either need to install the package or add the root directory to your
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Python path:
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</para>
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<para>
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<screen>
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$ export PYTHONPATH=$PYTHONPATH:`pwd`
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</screen>
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</para>
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<para>
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Try running examples:
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</para>
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<para>
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<screen>
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$ cd examples/gstreamer/
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$ python cp.py <input file> <output file>
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$ cmp <input file> <output file>
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$ python vorbisplay.py <an Ogg Vorbis file>
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</screen>
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</para>
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</section>
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<!--=================-->
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</section>
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<!--=====================================================================-->
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<section id="programming">
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<title>Programming</title>
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<!--=================-->
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<section id="general-api">
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<title>General API</title>
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<para>
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The gst-python bindings are directly generated from the GStreamer headers. Look at the GStreamer documentation at <ulink url="http://gstreamer.freedesktop.org/documentation/"/> for general API and programming issues. In most cases the GStreamer classes and boxed types map directly to Python classes. The function-based GObject methods also map onto Python methods.
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</para>
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</section>
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<!--=================-->
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<section id="divergence-from-c-api">
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<title>Divergence From C API</title>
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<para>Due to the nature of C and Python some of the GStreamer API is handled
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slightly different in Python than C. There are a few of the GStreamer C
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functions that are not yet provided in gst-python. These are mostly related to
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creating <xref linkend="python-elements" endterm="python-elements.title"/>. A
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few others remain that return GList* or return values in their parameters.
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These have been wrapped as needed. Please file a <link
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linkend="bugs">bug</link> if you need one of the unwrapped functions.</para>
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<para>API changes:</para>
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<itemizedlist>
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<listitem><para><function>gst_props_entry_get_type</function> is accessed
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through <function>PropsEntry.get_props_type</function>(). This is due to the
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<function>_get_type</function> function extention being normally used for
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<function>GType</function> access and is inaccessable
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otherwise.</para></listitem>
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<listitem><para>Special <link linkend="pipeline-iteration">pipeline
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iteration</link> support through the following functions:</para>
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<itemizedlist>
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<listitem><para><function>add_iterate_bin</function>(<parameter
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class="function">bin</parameter>) -> <returnvalue>id</returnvalue>: used
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to iterate a bin with a C idle loop callback instead of a Python
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callback.</para></listitem>
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<listitem><para><function>remove_iterate_bin</function>(<parameter
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class="function">id</parameter>): used to remove the
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<function>add_iterate_bin</function> idle loop callback
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id.</para></listitem>
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<listitem><para><function>iterate_bin_all</function>(<parameter
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class="function">bin</parameter>): releases locks, calls
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<function>gst_bin_iterate</function> until it returns 0, reacquires locks
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and completes</para></listitem>
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</itemizedlist>
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</listitem>
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<listitem><para><link linkend="python-elements">Python Elements</link> support through the following currently horribly inefficient functions:</para>
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<itemizedlist>
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<listitem><para><function>Buffer.get_data</function>() ->
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<returnvalue>string</returnvalue>: converts buffer data to a string and
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returns it.</para></listitem>
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<listitem><para><function>Buffer.set_data</function>(<parameter
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class="function">string</parameter>): sets the buffer data from a
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string.</para></listitem>
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</itemizedlist>
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</listitem>
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</itemizedlist>
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</section>
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<!--=================-->
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<section id="examples">
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<title>Examples</title>
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<para>The best documentation right now are the examples in <filename
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class="directory">./examples/gstreamer/</filename>. Read them.</para>
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</section>
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<!--=================-->
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<section id="threads">
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<title>Threads</title>
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<para>Threading is a tricky subject for gst-python. There are a few lock you
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need to be aware of:</para>
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<section id="gil">
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<title>GIL</title>
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<para>The CPython interpreter is single threaded. Code execution in the
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interpreter is protected by a Global Interpreter Lock (GIL). This means that C
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code can run in other threads in parallel but only one thread will be running
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Python code at any one point. Most of this is handled internally by means of
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locking and unlocking the GIL at appropriate times. Callback code and other
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various code paths between Python and C *should* be setup to do proper GIL
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handling.</para>
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<para>However, it is possible that you may encounter a situation where proper
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locking is not done. This is most likely due to calling a wrapper function
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that follows a sequence like this:</para>
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<orderedlist>
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<listitem><para>Python calls wrapper function</para></listitem>
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<listitem><para>wrapper function calls C GStreamer function</para></listitem>
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<listitem><para>C GStreamer function calls side effect code</para></listitem>
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<listitem><para>side effect code calls callback</para></listitem>
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<listitem><para>callback tries to acquire Python GIL but it's already locked</para></listitem>
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<listitem><para>deadlocked...</para></listitem>
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</orderedlist>
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<para>This has been fixed for commonly called functions that have side effects
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which are likely to re-enter the interpreter. It just involves lock/unlock
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around the call to the C gst function. But doing it for every function could
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have performance issues and, more importantly, is not an automated
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process.</para>
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<para>Please file a <link linkend="bugs">bug</link> if you have problems
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related to this and need other functions to be specially handled.</para>
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</section>
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<section id="gdk-lock">
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<title>Gdk Lock</title>
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<para>If you are using PyGTK you will have to deal with Gdk locking. Make sure
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you're holding the Gdk lock while executing Gdk/Gtk calls. See PyGTK
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documentation and FAQ list for more information.</para>
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</section>
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</section>
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<!--=================-->
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<section id="pipeline-iteration">
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<title>Pipeline Iteration</title>
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<para>There are a number of ways to iterate pipelines.
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<filename>./examples/gstreamer/bps.py</filename> is a small test program to
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measure the performance in buffers per second of these various techniques.
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Please see the example for how to use these techniques.</para>
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<itemizedlist>
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<listitem><para><function>Bin.iterate</function>() in Python from the gtk idle loop</para></listitem>
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<listitem><para><function>gst_bin_iterate</function>() in C from gtk idle loop</para></listitem>
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<listitem><para><function>Bin.iterate</function>() in a Python loop</para></listitem>
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<listitem><para><function>gst_bin_iterate</function>() in a C loop</para></listitem>
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</itemizedlist>
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<para>The method you chose depends on your application. The idle loop methods
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are slightly slower yet more flexible. Probably useful for interactive GUI
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applications.</para>
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<para>The basic loop methods are faster but probably more use for
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non-interactive applications. A variation on these loops would be to also
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check for a stop condition which may provide performance increase and some
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level of control.</para>
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</section>
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<!--=================-->
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<section id="python-elements">
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<title id="python-elements.title">Python Elements</title>
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<para> It is possible to write Python subclasses of GstElement. This support
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is very primitive and likely to change. See
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<filename>./examples/gstreamer/rot13.py</filename> for an example.</para>
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</section>
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<!--=================-->
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</section>
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<!--=====================================================================-->
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<section id="bugs">
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<title>Bugs</title>
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<para>
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<emphasis>Please</emphasis> submit gst-python bugs, patches, or suggestions to GNOME Bugzilla (<ulink url="http://bugzilla.gnome.org/"/>). Product: GStreamer, Component: gst-python. Or alternatively send a message to the gstreamer-devel list or the maintainer. Thank you.
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</para>
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</section>
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<!--=====================================================================-->
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<xi:include href="TODO.xml#todo" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<!--=====================================================================-->
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<xi:include href="AUTHORS.xml#authors" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<!--=====================================================================-->
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</article>
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