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312 lines
13 KiB
XML
312 lines
13 KiB
XML
<chapter id="chapter-porting">
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<title>Porting 0.8 applications to 0.10</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;-0.10, 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;-0.10 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 thread safety. 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. It is important that all objects
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derived from GstObject are ref'ed/unref'ed using gst_object_ref()
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and gst_object_unref() respectively (instead of g_object_ref/unref).
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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 a
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main loop, 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). Due to the new fully threaded
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nature of GStreamer-0.10, state changes are not always immediate,
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in particular changes including the transition from READY to PAUSED
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state. This means two things in the context of porting applications:
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first of all, it is no longer always possible to do
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<function>gst_element_set_state ()</function> and check for a return
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value of GST_STATE_CHANGE_SUCCESS, as the state change might be
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delayed (ASYNC) and the result will not be known until later. You
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should still check for GST_STATE_CHANGE_FAILURE right away, it is
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just no longer possible to assume that everything that is not SUCCESS
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means failure. Secondly, state changes might not be immediate, so
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your code needs to take that into account. You can wait for a state
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change to complete if you use GST_CLOCK_TIME_NONE as timeout interval
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with <function>gst_element_get_state ()</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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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 0.10. In 0.10, 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 -> capsfilter element (the pipeline syntax for
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gst-launch has not changed though).
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</para>
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</listitem>
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<listitem>
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<para>
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libgstgconf-0.10.la does not exist. Use the
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<quote>gconfvideosink</quote> and <quote>gconfaudiosink</quote>
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elements instead, which will do live-updates and require no library
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linking.
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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 <quote>new-pad</quote> and <quote>state-change</quote> signals on
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<classname>GstElement</classname> were renamed to
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<quote>pad-added</quote> and <quote>state-changed</quote>.
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</para>
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</listitem>
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<listitem>
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<para>
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<function>gst_init_get_popt_table ()</function> has been removed
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in favour of the new GOption command line option API that was
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added to GLib 2.6. <function>gst_init_get_option_group ()</function>
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is the new GOption-based equivalent to
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<function>gst_init_get_ptop_table ()</function>.
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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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<chapter id="chapter-porting-1.0">
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<title>Porting 0.10 applications to 1.0</title>
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<para>This section outlines some of the changes necessary to port
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applications from &GStreamer;-0.10 to &GStreamer;-1.0. For a
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comprehensive and up-to-date list, see the separate <ulink
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type="http"
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url="http://cgit.freedesktop.org/gstreamer/gstreamer/plain/docs/random/porting-to-1.0.txt">
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Porting to 1.0</ulink> document.
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</para>
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<para>
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It should be possible to port simple applications to
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&GStreamer;-1.0 in less than a day.
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</para>
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<sect1 id="section-porting-objects-1.0">
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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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All deprecated methods were removed. Recompile against 0.10 with
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GST_DISABLE_DEPRECATED defined (such as by adding
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-DGST_DISABLE_DEPRECATED to the compiler flags) and fix issues
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before attempting to port to 1.0.
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</para>
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</listitem>
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<listitem>
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<para>
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"playbin2" has been renamed to "playbin", with similar API
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</para>
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</listitem>
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<listitem>
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<para>
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"decodebin2" has been renamed to "decodebin", with similar API. Note
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that there is no longer a "new-decoded-pad" signal, just use GstElement's
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"pad-added" signal instead (but don't forget to remove the 'gboolean last'
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argument from your old signal callback functino signature).
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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 names of some "formatted" pad templates has been changed from e.g.
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"src%d" to "src%u" or "src_%u" or similar, since we don't want to see
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negative numbers in pad names. This mostly affects applications that
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create request pads from elements.
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</para>
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</listitem>
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<listitem>
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<para>
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some elements that used to have a single dynamic source pad have a
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source pad now. Example: wavparse, id3demux, iceydemux, apedemux.
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(This does not affect applications using decodebin or playbin).
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</para>
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</listitem>
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<listitem>
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<para>
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playbin now proxies the GstVideoOverlay (former GstXOverlay) interface,
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so most applications can just remove the sync bus handler where they
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would set the window ID, and instead just set the window ID on playbin
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from the application thread before starting playback.
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</para>
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<para>
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playbin also proxies the GstColorBalance and GstNavigation interfaces,
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so applications that use this don't need to go fishing for elements
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that may implement those any more, but can just use on playbin
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unconditionally.
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</para>
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</listitem>
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<listitem>
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<para>
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multifdsink, tcpclientsink, tcpclientsrc, tcpserversrc the protocol property
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is removed, use gdppay and gdpdepay.
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</para>
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</listitem>
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<listitem>
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<para>
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XML serialization was removed.
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</para>
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</listitem>
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<listitem>
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<para>
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Probes and pad blocking was merged into new pad probes.
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</para>
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</listitem>
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<listitem>
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<para>
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Position, duration and convert functions no longer use an inout parameter
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for the destination format.
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</para>
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</listitem>
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<listitem>
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<para>
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Video and audio caps were simplified. audio/x-raw-int and audio/x-raw-float
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are now all under the audio/x-raw media type. Similarly, video/x-raw-rgb
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and video/x-raw-yuv are now video/x-raw.
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</para>
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</listitem>
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<listitem>
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<para>
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ffmpegcolorspace was removed and replaced with videoconvert.
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</para>
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</listitem>
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<listitem>
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<para>
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GstMixerInterface / GstTunerInterface were removed without replacement.
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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 GstXOverlay interface was renamed to GstVideoOverlay, and now part
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of the video library in gst-plugins-base, as the interfaces library
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no longer exists.
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</para>
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<para>
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The name of the GstXOverlay "prepare-xwindow-id" message has changed
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to "prepare-window-handle" (and GstXOverlay has been renamed to
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GstVideoOverlay). Code that checks for the string directly should be
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changed to use gst_is_video_overlay_prepare_window_handle_message(message)
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instead.
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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 GstPropertyProbe interface was removed. the is no replacement yet,
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but a more featureful replacement for device discovery and feature
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querying is planned, see https://bugzilla.gnome.org/show_bug.cgi?id=678402
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</para>
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</listitem>
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<listitem>
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<para>
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gst_uri_handler_get_uri() and the get_uri vfunc now return a copy of
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the URI string
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</para>
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<para>
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gst_uri_handler_set_uri() and the set_uri vfunc now take an additional
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GError argument so the handler can notify the caller why it didn't
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accept a particular URI.
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</para>
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<para>
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gst_uri_handler_set_uri() now checks if the protocol of the URI passed
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is one of the protocols advertised by the uri handler, so set_uri vfunc
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implementations no longer need to check that as well.
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</para>
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</listitem>
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<listitem>
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<para>
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GstTagList is now an opaque mini object instead of being typedefed to a
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GstStructure. While it was previously okay (and in some cases required because of
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missing taglist API) to cast a GstTagList to a GstStructure or use
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gst_structure_* API on taglists, you can no longer do that. Doing so will
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cause crashes.
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</para>
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<para>
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Also, tag lists are refcounted now, and can therefore not be freely
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modified any longer. Make sure to call gst_tag_list_make_writable (taglist)
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before adding, removing or changing tags in the taglist.
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</para>
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<para>
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GST_TAG_IMAGE, GST_TAG_PREVIEW_IMAGE, GST_TAG_ATTACHMENT: many tags that
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used to be of type GstBuffer are now of type GstSample (which is basically
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a struct containing a buffer alongside caps and some other info).
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</para>
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</listitem>
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<listitem>
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<para>
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GstController has now been merged into GstObject. It does not exists as an
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individual object anymore. In addition core contains a GstControlSource base
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class and the GstControlBinding. The actual control sources are in the controller
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library as before. The 2nd big change is that control sources generate
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a sequence of gdouble values and those are mapped to the property type and
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value range by GstControlBindings.
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</para>
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<para>
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The whole gst_controller_* API is gone and now available in simplified form
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under gst_object_*. ControlSources are now attached via GstControlBinding
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to properties. There are no GValue arguments used anymore when programming
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control sources.
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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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