mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-27 20:21:24 +00:00
332 lines
11 KiB
XML
332 lines
11 KiB
XML
<?xml version="1.0"?>
|
|
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
|
|
<!ENTITY % local.common.attrib "xml:base CDATA #IMPLIED">
|
|
<!ENTITY % ents SYSTEM "gst-python.ent">
|
|
%ents;
|
|
]>
|
|
|
|
<article id="gst-python">
|
|
<articleinfo>
|
|
<title>Gst-Python &version;: A Python Interface to GStreamer</title>
|
|
<publisher><publishername>The GStreamer Development Team</publishername></publisher>
|
|
<pubdate>&pubdate;</pubdate>
|
|
<copyright><year>2003</year><holder>David I. Lehn</holder></copyright>
|
|
<titleabbrev>gst-python</titleabbrev>
|
|
<authorgroup>
|
|
<author>
|
|
<firstname>David</firstname>
|
|
<othername role="mi">I.</othername>
|
|
<surname>Lehn</surname>
|
|
<email>dlehn@users.sourceforge.net</email>
|
|
</author>
|
|
</authorgroup>
|
|
<abstract>
|
|
<para>Introductory information for the GStreamer Python bindings.</para>
|
|
<para><ulink url="http://www.gstreamer.net/bindings/python/"/></para>
|
|
</abstract>
|
|
<revhistory>
|
|
<revision>
|
|
<revnumber>0.1.0</revnumber>
|
|
<date>2003-07-10</date>
|
|
<authorinitials>dil</authorinitials>
|
|
<revremark>Initial version.</revremark>
|
|
</revision>
|
|
</revhistory>
|
|
</articleinfo>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<section id="about">
|
|
<title>About</title>
|
|
<para>
|
|
|
|
<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.
|
|
|
|
</para>
|
|
</section>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<xi:include href="NEWS.xml#news" xmlns:xi="http://www.w3.org/2001/XInclude"/>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<section id="installation">
|
|
<title>Installation</title>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="requirements">
|
|
<title>Requirements</title>
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
Python 2.2 (<ulink url="http://www.python.org/"/>)
|
|
</para></listitem>
|
|
<listitem><para>
|
|
GStreamer 0.6.x (<emphasis>except</emphasis> 0.6.1) (<ulink url="http://www.gstreamer.net/"/>)
|
|
</para></listitem>
|
|
<listitem><para>
|
|
PyGTK 1.99.14 (<ulink url="http://www.daa.com.au/~james/pygtk/"/>)
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="building">
|
|
<title>Building and Installation</title>
|
|
|
|
<para>
|
|
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:
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
$ ./configure && make
|
|
</screen>
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="using">
|
|
<title>Using</title>
|
|
<para>
|
|
You either need to install the package or add the root directory to your
|
|
Python path:
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
$ export PYTHONPATH=$PYTHONPATH:`pwd`
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Try running examples:
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
$ cd examples/gstreamer/
|
|
$ python cp.py <input file> <output file>
|
|
$ cmp <input file> <output file>
|
|
$ python vorbisplay.py <an Ogg Vorbis file>
|
|
</screen>
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
</section>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<section id="programming">
|
|
<title>Programming</title>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="general-api">
|
|
<title>General API</title>
|
|
<para>
|
|
|
|
The gst-python bindings are directly generated from the GStreamer headers. Look at the GStreamer documentation at <ulink url="http://www.gstreamer.net/docs/"/> 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.
|
|
|
|
</para>
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="divergence-from-c-api">
|
|
<title>Divergence From C API</title>
|
|
|
|
<para>Due to the nature of C and Python some of the GStreamer API is handled
|
|
slightly different in Python than C. There are a few of the GStreamer C
|
|
functions that are not yet provided in gst-python. These are mostly related to
|
|
creating <xref linkend="python-elements" endterm="python-elements.title"/>. A
|
|
few others remain that return GList* or return values in their parameters.
|
|
These have been wrapped as needed. Please file a <link
|
|
linkend="bugs">bug</link> if you need one of the unwrapped functions.</para>
|
|
|
|
<para>API changes:</para>
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para><function>gst_props_entry_get_type</function> is accessed
|
|
through <function>PropsEntry.get_props_type</function>(). This is due to the
|
|
<function>_get_type</function> function extention being normally used for
|
|
<function>GType</function> access and is inaccessable
|
|
otherwise.</para></listitem>
|
|
|
|
<listitem><para>Special <link linkend="pipeline-iteration">pipeline
|
|
iteration</link> support through the following functions:</para>
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para><function>add_iterate_bin</function>(<parameter
|
|
class="function">bin</parameter>) -> <returnvalue>id</returnvalue>: used
|
|
to iterate a bin with a C idle loop callback instead of a Python
|
|
callback.</para></listitem>
|
|
|
|
<listitem><para><function>remove_iterate_bin</function>(<parameter
|
|
class="function">id</parameter>): used to remove the
|
|
<function>add_iterate_bin</function> idle loop callback
|
|
id.</para></listitem>
|
|
|
|
<listitem><para><function>iterate_bin_all</function>(<parameter
|
|
class="function">bin</parameter>): releases locks, calls
|
|
<function>gst_bin_iterate</function> until it returns 0, reacquires locks
|
|
and completes</para></listitem>
|
|
|
|
</itemizedlist>
|
|
</listitem>
|
|
|
|
<listitem><para><link linkend="python-elements">Python Elements</link> support through the following currently horribly inefficient functions:</para>
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem><para><function>Buffer.get_data</function>() ->
|
|
<returnvalue>string</returnvalue>: converts buffer data to a string and
|
|
returns it.</para></listitem>
|
|
|
|
<listitem><para><function>Buffer.set_data</function>(<parameter
|
|
class="function">string</parameter>): sets the buffer data from a
|
|
string.</para></listitem>
|
|
|
|
</itemizedlist>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="examples">
|
|
<title>Examples</title>
|
|
|
|
<para>The best documentation right now are the examples in <filename
|
|
class="directory">./examples/gstreamer/</filename>. Read them.</para>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="threads">
|
|
<title>Threads</title>
|
|
|
|
<para>Threading is a tricky subject for gst-python. There are a few lock you
|
|
need to be aware of:</para>
|
|
|
|
<section id="gil">
|
|
<title>GIL</title>
|
|
|
|
<para>The CPython interpreter is single threaded. Code execution in the
|
|
interpreter is protected by a Global Interpreter Lock (GIL). This means that C
|
|
code can run in other threads in parallel but only one thread will be running
|
|
Python code at any one point. Most of this is handled internally by means of
|
|
locking and unlocking the GIL at appropriate times. Callback code and other
|
|
various code paths between Python and C *should* be setup to do proper GIL
|
|
handling.</para>
|
|
|
|
<para>However, it is possible that you may encounter a situation where proper
|
|
locking is not done. This is most likely due to calling a wrapper function
|
|
that follows a sequence like this:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>Python calls wrapper function</para></listitem>
|
|
<listitem><para>wrapper function calls C GStreamer function</para></listitem>
|
|
<listitem><para>C GStreamer function calls side effect code</para></listitem>
|
|
<listitem><para>side effect code calls callback</para></listitem>
|
|
<listitem><para>callback tries to acquire Python GIL but it's already locked</para></listitem>
|
|
<listitem><para>deadlocked...</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>This has been fixed for commonly called functions that have side effects
|
|
which are likely to re-enter the interpreter. It just involves lock/unlock
|
|
around the call to the C gst function. But doing it for every function could
|
|
have performance issues and, more importantly, is not an automated
|
|
process.</para>
|
|
|
|
<para>Please file a <link linkend="bugs">bug</link> if you have problems
|
|
related to this and need other functions to be specially handled.</para>
|
|
|
|
</section>
|
|
|
|
<section id="gdk-lock">
|
|
<title>Gdk Lock</title>
|
|
|
|
<para>If you are using PyGTK you will have to deal with Gdk locking. Make sure
|
|
you're holding the Gdk lock while executing Gdk/Gtk calls. See PyGTK
|
|
documentation and FAQ list for more information.</para>
|
|
|
|
</section>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="pipeline-iteration">
|
|
<title>Pipeline Iteration</title>
|
|
|
|
<para>There are a number of ways to iterate pipelines.
|
|
<filename>./examples/gstreamer/bps.py</filename> is a small test program to
|
|
measure the performance in buffers per second of these various techniques.
|
|
Please see the example for how to use these techniques.</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para><function>Bin.iterate</function>() in Python from the gtk idle loop</para></listitem>
|
|
<listitem><para><function>gst_bin_iterate</function>() in C from gtk idle loop</para></listitem>
|
|
<listitem><para><function>Bin.iterate</function>() in a Python loop</para></listitem>
|
|
<listitem><para><function>gst_bin_iterate</function>() in a C loop</para></listitem>
|
|
</itemizedlist>
|
|
|
|
<para>The method you chose depends on your application. The idle loop methods
|
|
are slightly slower yet more flexible. Probably useful for interactive GUI
|
|
applications.</para>
|
|
|
|
<para>The basic loop methods are faster but probably more use for
|
|
non-interactive applications. A variation on these loops would be to also
|
|
check for a stop condition which may provide performance increase and some
|
|
level of control.</para>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
<section id="python-elements">
|
|
<title id="python-elements.title">Python Elements</title>
|
|
|
|
<para> It is possible to write Python subclasses of GstElement. This support
|
|
is very primitive and likely to change. See
|
|
<filename>./examples/gstreamer/rot13.py</filename> for an example.</para>
|
|
|
|
</section>
|
|
|
|
<!--=================-->
|
|
|
|
</section>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<section id="bugs">
|
|
<title>Bugs</title>
|
|
<para>
|
|
<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.
|
|
</para>
|
|
</section>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<xi:include href="TODO.xml#todo" xmlns:xi="http://www.w3.org/2001/XInclude"/>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
<xi:include href="AUTHORS.xml#authors" xmlns:xi="http://www.w3.org/2001/XInclude"/>
|
|
|
|
<!--=====================================================================-->
|
|
|
|
</article>
|