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Original commit message from CVS: * docs/manual/advanced-clocks.xml: * docs/manual/advanced-interfaces.xml: * docs/manual/advanced-metadata.xml: * docs/manual/advanced-position.xml: * docs/manual/advanced-schedulers.xml: * docs/manual/advanced-threads.xml: * docs/manual/appendix-porting.xml: * docs/manual/basics-bins.xml: * docs/manual/basics-bus.xml: * docs/manual/basics-elements.xml: * docs/manual/basics-helloworld.xml: * docs/manual/basics-pads.xml: * docs/manual/highlevel-components.xml: * docs/manual/manual.xml: * docs/manual/thread.fig: Update (until threads/scheduling) Application Development Manual; remove GstThread, add GstBus, add simple porting checklist, add documentation for tag writing, clocks, make all examples until this part compile and run. * examples/manual/Makefile.am: Update from changes to Application Development Manual; add bus example, remove thread example.
90 lines
4 KiB
XML
90 lines
4 KiB
XML
<chapter id="chapter-porting">
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<title>Porting 0.8 applications to 0.9</title>
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<para>
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This section of the appendix will discuss shortly what changes to
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applications will be needed to quickly and conveniently port most
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applications from &GStreamer;-0.8 to &GStreamer;-0.9, with references
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to the relevant sections in this Application Development Manual
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where needed. With this list, it should be possible to port simple
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applications to &GStreamer;-0.9 in less than a day.
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</para>
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<sect1 id="section-porting-objects">
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<title>List of changes</title>
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<itemizedlist>
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<listitem>
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<para>
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Most functions returning an object or an object property have
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been changed to return its own reference rather than a constant
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reference of the one owned by the object itself. The reason for
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this change is primarily threadsafety. This means, effectively,
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that return values of functions such as
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<function>gst_element_get_pad ()</function>,
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<function>gst_pad_get_name ()</function> and many more like these
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have to be free'ed or unreferenced after use. Check the API
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references of each function to know for sure whether return
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values should be free'ed or not.
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</para>
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</listitem>
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<listitem>
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<para>
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Applications should no longer use signal handlers to be notified
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of errors, end-of-stream and other similar pipeline events.
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Instead, they should use the <classname>GstBus</classname>, which
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has been discussed in <xref linkend="chapter-bus"/>. The bus will
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take care that the messages will be delivered in the context of
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mainloop, which is almost certainly the application's main thread.
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The big advantage of this is that applications no longer need to
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be thread-aware; they don't need to use <function>g_idle_add
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()</function> in the signal handler and do the actual real work
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in the idle-callback. &GStreamer; now does all that internally.
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</para>
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</listitem>
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<listitem>
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<para>
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Related to this, <function>gst_bin_iterate ()</function> has been
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removed. Pipelines will iterate in their own thread, and applications
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can simply run a <classname>GMainLoop</classname> (or call the
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mainloop of their UI toolkit, such as <function>gtk_main
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()</function>).
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</para>
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</listitem>
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<listitem>
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<para>
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State changes can be delayed; ASYNC.
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</para>
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</listitem>
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<listitem>
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<para>
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In 0.8, events and queries had to manually be sent to sinks in
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pipelines (unless you were using playbin). This is no longer
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the case in 0.9. In 0.9, queries and events can be sent to
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toplevel pipelines, and the pipeline will do the dispatching
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internally for you. This means less bookkeeping in your
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application. For a short code example, see <xref
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linkend="chapter-queryevents"/>. Related, seeking is now
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threadsafe, and your video output will show the new video
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position's frame while seeking, providing a better user
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experience.
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</para>
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</listitem>
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<listitem>
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<para>
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The <classname>GstThread</classname> object has been removed.
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Applications can now simply put elements in a pipeline with
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optionally some <quote>queue</quote> elements in between for
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buffering, and &GStreamer; will take care of creating threads
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internally. It is still possible to have parts of a pipeline
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run in different threads than others, by using the
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<quote>queue</quote> element. See <xref linkend="chapter-threads"/>
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for details.
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</para>
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</listitem>
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<listitem>
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<para>
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Filtered caps -> caps-filter.
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</para>
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</listitem>
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</itemizedlist>
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</sect1>
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</chapter>
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