gstreamer/docs/manual/appendix-porting.xml

<chapter id="chapter-porting">
  <title>Porting 0.8 applications to 0.10</title>
  <para>
    This section of the appendix will discuss shortly what changes to
    applications will be needed to quickly and conveniently port most
    applications from &GStreamer;-0.8 to &GStreamer;-0.10, with references
    to the relevant sections in this Application Development Manual
    where needed. With this list, it should be possible to port simple
    applications to &GStreamer;-0.10 in less than a day.
  </para>

  <sect1 id="section-porting-objects">
    <title>List of changes</title>
    <itemizedlist>
      <listitem>
        <para>
          Most functions returning an object or an object property have
          been changed to return its own reference rather than a constant
          reference of the one owned by the object itself. The reason for
          this change is primarily thread safety. This means, effectively,
          that return values of functions such as
          <function>gst_element_get_pad ()</function>,
          <function>gst_pad_get_name ()</function> and many more like these
          have to be free'ed or unreferenced after use. Check the API
          references of each function to know for sure whether return
          values should be free'ed or not. It is important that all objects
          derived from GstObject are ref'ed/unref'ed using gst_object_ref()
          and gst_object_unref() respectively (instead of g_object_ref/unref).
        </para>
      </listitem>
      <listitem>
        <para>
          Applications should no longer use signal handlers to be notified
          of errors, end-of-stream and other similar pipeline events.
          Instead, they should use the <classname>GstBus</classname>, which
          has been discussed in <xref linkend="chapter-bus"/>. The bus will
          take care that the messages will be delivered in the context of a
          main loop, which is almost certainly the application's main thread.
          The big advantage of this is that applications no longer need to
          be thread-aware; they don't need to use <function>g_idle_add
          ()</function> in the signal handler and do the actual real work
          in the idle-callback. &GStreamer; now does all that internally.
        </para>
      </listitem>
      <listitem>
        <para>
          Related to this, <function>gst_bin_iterate ()</function> has been
          removed. Pipelines will iterate in their own thread, and applications
          can simply run a <classname>GMainLoop</classname> (or call the
          mainloop of their UI toolkit, such as <function>gtk_main
          ()</function>).
        </para>
      </listitem>
      <listitem>
        <para>
          State changes can be delayed (ASYNC). Due to the new fully threaded
          nature of GStreamer-0.10, state changes are not always immediate,
          in particular changes including the transition from READY to PAUSED
          state. This means two things in the context of porting applications:
          first of all, it is no longer always possible to do
          <function>gst_element_set_state ()</function> and check for a return
          value of GST_STATE_CHANGE_SUCCESS, as the state change might be
          delayed (ASYNC) and the result will not be known until later. You
          should still check for GST_STATE_CHANGE_FAILURE right away, it is
          just no longer possible to assume that everything that is not SUCCESS
          means failure. Secondly, state changes might not be immediate, so
          your code needs to take that into account. You can wait for a state
          change to complete if you use GST_CLOCK_TIME_NONE as timeout interval
          with <function>gst_element_get_state ()</function>.
        </para>
      </listitem>
      <listitem>
        <para>
          In 0.8, events and queries had to manually be sent to sinks in
          pipelines (unless you were using playbin). This is no longer
          the case in 0.10. In 0.10, queries and events can be sent to
          toplevel pipelines, and the pipeline will do the dispatching
          internally for you. This means less bookkeeping in your
          application. For a short code example, see <xref
          linkend="chapter-queryevents"/>. Related, seeking is now
          threadsafe, and your video output will show the new video
          position's frame while seeking, providing a better user
          experience.
        </para>
      </listitem>
      <listitem>
        <para>
          The <classname>GstThread</classname> object has been removed.
          Applications can now simply put elements in a pipeline with
          optionally some <quote>queue</quote> elements in between for
          buffering, and &GStreamer; will take care of creating threads
          internally. It is still possible to have parts of a pipeline
          run in different threads than others, by using the
          <quote>queue</quote> element. See <xref linkend="chapter-threads"/>
          for details.
        </para>
      </listitem>
      <listitem>
        <para>
          Filtered caps -> capsfilter element (the pipeline syntax for
          gst-launch has not changed though).
        </para>
      </listitem>
      <listitem>
        <para>
          libgstgconf-0.10.la does not exist. Use the
          <quote>gconfvideosink</quote> and <quote>gconfaudiosink</quote>
          elements instead, which will do live-updates and require no library
          linking.
        </para>
      </listitem>
      <listitem>
        <para>
          The <quote>new-pad</quote> and <quote>state-change</quote> signals on
          <classname>GstElement</classname> were renamed to
          <quote>pad-added</quote> and <quote>state-changed</quote>.
        </para>
      </listitem>
      <listitem>
        <para>
          <function>gst_init_get_popt_table ()</function> has been removed
          in favour of the new GOption command line option API that was
          added to GLib 2.6. <function>gst_init_get_option_group ()</function>
          is the new GOption-based equivalent to
          <function>gst_init_get_ptop_table ()</function>.
        </para>
      </listitem>
    </itemizedlist>
  </sect1>
</chapter>
<chapter id="chapter-porting-1.0">
  <title>Porting 0.10 applications to 1.0</title>
  <para>
    This section of the appendix will discuss shortly what changes to
    applications will be needed to quickly and conveniently port most
    applications from &GStreamer;-0.10 to &GStreamer;-1.0, with references
    to the relevant sections in this Application Development Manual
    where needed. With this list, it should be possible to port simple
    applications to &GStreamer;-1.0 in less than a day.
  </para>

  <sect1 id="section-porting-objects-1.0">
    <title>List of changes</title>
    <itemizedlist>
      <listitem>
        <para>
          All deprecated methods were removed. Recompile against 0.10 with
          DISABLE_DEPRECATED and fix issues before attempting to port to 1.0.
        </para>
      </listitem>
      <listitem>
        <para>
          "playbin2" has been renamed to "playbin", with similar API
        </para>
      </listitem>
      <listitem>
        <para>
          "decodebin2" has been renamed to "decodebin", with similar API. Note
          that there is no longer a "new-decoded-pad" signal, just use GstElement's
          "pad-added" signal instead (but don't forget to remove the 'gboolean last'
          argument from your old signal callback functino signature).
        </para>
      </listitem>
      <listitem>
        <para>
          the names of some "formatted" pad templates has been changed from e.g.
          "src%d" to "src%u" or "src_%u" or similar, since we don't want to see
          negative numbers in pad names. This mostly affects applications that
          create request pads from elements.
        </para>
      </listitem>
      <listitem>
        <para>
          some elements that used to have a single dynamic source pad have a
          source pad now. Example: wavparse, id3demux, iceydemux, apedemux.
          (This does not affect applications using decodebin or playbin).
        </para>
      </listitem>
      <listitem>
        <para>
          playbin now proxies the GstVideoOverlay (former GstXOverlay) interface,
          so most applications can just remove the sync bus handler where they
          would set the window ID, and instead just set the window ID on playbin
          from the application thread before starting playback.
        </para>
        <para>
          playbin also proxies the GstColorBalance and GstNavigation interfaces,
          so applications that use this don't need to go fishing for elements
          that may implement those any more, but can just use them unconditionally.
        </para>
      </listitem>
      <listitem>
        <para>
          multifdsink, tcpclientsink, tcpclientsrc, tcpserversrc the protocol property
          is removed, use gdppay and gdpdepay.
        </para>
      </listitem>
      <listitem>
        <para>
          XML serialization was removed.
        </para>
      </listitem>
      <listitem>
        <para>
          Probes and pad blocking was merged into new pad probes.
        </para>
      </listitem>
      <listitem>
        <para>
          Position, duration and convert functions no longer use an inout parameter
          for the destination format.
        </para>
      </listitem>
      <listitem>
        <para>
          Video and audio caps were simplified. audio/x-raw-int and audio/x-raw-float
          are now all under the audio/x-raw media type. Similarly, video/x-raw-rgb
          and video/x-raw-yuv are now video/x-raw.
        </para>
      </listitem>
      <listitem>
        <para>
          ffmpegcolorspace was removed and replaced with videoconvert.
        </para>
      </listitem>
      <listitem>
        <para>
          GstMixerInterface / GstTunerInterface were removed without replacement.
        </para>
      </listitem>
      <listitem>
        <para>
          The GstXOverlay interface was renamed to GstVideoOverlay, and now part
          of the video library in gst-plugins-base, as the interfaces library
          no longer exists.
        </para>
        <para>
          The name of the GstXOverlay "prepare-xwindow-id" message has changed
          to "prepare-window-handle" (and GstXOverlay has been renamed to
          GstVideoOverlay). Code that checks for the string directly should be
          changed to use gst_is_video_overlay_prepare_window_handle_message(message)
          instead.
        </para>
      </listitem>
      <listitem>
        <para>
          The GstPropertyProbe interface was removed. the is no replacement yet,
          but a more featureful replacement for device discovery and feature
          querying is planned, see https://bugzilla.gnome.org/show_bug.cgi?id=678402
        </para>
      </listitem>
      <listitem>
        <para>
          gst_uri_handler_get_uri() and the get_uri vfunc now return a copy of
          the URI string
        </para>
        <para>
          gst_uri_handler_set_uri() and the set_uri vfunc now take an additional
          GError argument so the handler can notify the caller why it didn't
          accept a particular URI.
        </para>
        <para>
          gst_uri_handler_set_uri() now checks if the protocol of the URI passed
          is one of the protocols advertised by the uri handler, so set_uri vfunc
          implementations no longer need to check that as well.
        </para>
      </listitem>
      <listitem>
        <para>
          GstTagList is now an opaque mini object instead of being typedefed to a
          GstStructure. While it was previously okay (and in some cases required because of
          missing taglist API) to cast a GstTagList to a GstStructure or use
          gst_structure_* API on taglists, you can no longer do that. Doing so will
          cause crashes.
        </para>
        <para>
          Also, tag lists are refcounted now, and can therefore not be freely
          modified any longer. Make sure to call gst_tag_list_make_writable (taglist)
          before adding, removing or changing tags in the taglist.
        </para>
        <para>
          GST_TAG_IMAGE, GST_TAG_PREVIEW_IMAGE, GST_TAG_ATTACHMENT: many tags that
          used to be of type GstBuffer are now of type GstSample (which is basically
          a struct containing a buffer alongside caps and some other info).
        </para>
      </listitem>
      <listitem>
        <para>
          GstController has now been merged into GstObject. It does not exists as an
          individual object anymore. In addition core contains a GstControlSource base
          class and the GstControlBinding. The actual control sources are in the controller
          library as before. The 2nd big change is that control sources generate
          a sequence of gdouble values and those are mapped to the property type and
          value range by GstControlBindings.
        </para>
        <para>
          The whole gst_controller_* API is gone and now available in simplified form
          under gst_object_*. ControlSources are now attached via GstControlBinding
          to properties. There are no GValue arguments used anymore when programming
          control sources.
        </para>
      </listitem>
    </itemizedlist>
  </sect1>
</chapter>