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251 lines
8.1 KiB
XML
251 lines
8.1 KiB
XML
<chapter id="cha-programs">
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<title>Programs</title>
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<para>
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</para>
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<sect1>
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<title><command>gst-register</command></title>
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<para>
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<command>gst-register</command> is used to rebuild the database of plugins.
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It is used after a new plugin has been added to the system. The plugin database
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can be found, by default, in <filename>/etc/gstreamer/reg.xml</filename>.
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</para>
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</sect1>
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<sect1>
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<title><command>gst-launch</command></title>
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<para>
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This is a tool that will construct pipelines based on a command-line
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syntax.
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</para>
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<para>
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A simple commandline looks like:
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<screen>
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gst-launch filesrc location=hello.mp3 ! mad ! osssink
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</screen>
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A more complex pipeline looks like:
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<screen>
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gst-launch filesrc location=redpill.vob ! mpegdemux name=demux \
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demux.audio_00! { ac3parse ! a52dec ! osssink } \
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demux.video_00! { mpeg2dec ! xvideosink }
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</screen>
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</para>
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<para>
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You can also use the parser in you own
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code. <application>GStreamer</application> provides a function
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gst_parse_launch () that you can use to construct a pipeline.
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The following program lets you create an MP3 pipeline using the
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gst_parse_launch () function:
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</para>
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<programlisting>
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#include <gst/gst.h>
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int
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main (int argc, char *argv[])
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{
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GstElement *pipeline;
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GstElement *filesrc;
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GError *error = NULL;
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gst_init (&argc, &argv);
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if (argc != 2) {
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g_print ("usage: %s <filename>\n", argv[0]);
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return -1;
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}
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pipeline = gst_parse_launch ("filesrc name=my_filesrc ! mad ! osssink", &error);
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if (!pipeline) {
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g_print ("Parse error: %s\n", error->message);
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exit (1);
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}
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filesrc = gst_bin_get_by_name (GST_BIN (pipeline), "my_filesrc");
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g_object_set (G_OBJECT (filesrc), "location", argv[1], NULL);
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gst_element_set_state (pipeline, GST_STATE_PLAYING);
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while (gst_bin_iterate (GST_BIN (pipeline)));
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gst_element_set_state (pipeline, GST_STATE_NULL);
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return 0;
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}
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</programlisting>
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<para>
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Note how we can retrieve the filesrc element from the constructed bin using the
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element name.
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</para>
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<sect2>
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<title>Grammar Reference</title>
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<para>
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The <command>gst-launch</command> syntax is processed by a flex/bison parser. This section
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is intended to provide a full specification of the grammar; any deviations from this
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specification is considered a bug.
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</para>
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<sect3>
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<title>Elements</title>
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<screen>
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... mad ...
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</screen>
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<para>
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A bare identifier (a string beginning with a letter and containing
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only letters, numbers, dashes, underscores, percent signs, or colons)
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will create an element from a given element factory. In this example,
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an instance of the "mad" MP3 decoding plugin will be created.
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</para>
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</sect3>
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<sect3>
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<title>Links</title>
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<screen>
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... !sink ...
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</screen>
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<para>
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An exclamation point, optionally having a qualified pad name (an the name of the pad,
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optionally preceded by the name of the element) on both sides, will link two pads. If
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the source pad is not specified, a source pad from the immediately preceding element
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will be automatically chosen. If the sink pad is not specified, a sink pad from the next
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element to be constructed will be chosen. An attempt will be made to find compatible
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pads. Pad names may be preceded by an element name, as in
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<computeroutput>my_element_name.sink_pad</computeroutput>.
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</para>
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</sect3>
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<sect3>
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<title>Properties</title>
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<screen>
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... location="http://gstreamer.net" ...
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</screen>
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<para>
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The name of a property, optionally qualified with an element name, and a value,
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separated by an equals sign, will set a property on an element. If the element is not
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specified, the previous element is assumed. Strings can optionally be enclosed in
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quotation marks. Characters in strings may be escaped with the backtick
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(<literal>\</literal>). If the right-hand side is all digits, it is considered to be an
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integer. If it is all digits and a decimal point, it is a double. If it is "true",
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"false", "TRUE", or "FALSE" it is considered to be boolean. Otherwise, it is parsed as a
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string. The type of the property is determined later on in the parsing, and the value is
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converted to the target type. This conversion is not guaranteed to work, it relies on
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the g_value_convert routines. No error message will be displayed on an invalid
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conversion, due to limitations in the value convert API.
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</para>
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</sect3>
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<sect3>
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<title>Bins, Threads, and Pipelines</title>
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<screen>
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( ... )
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</screen>
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<para>
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A pipeline description between parentheses is placed into a bin. The open paren may be
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preceded by a type name, as in <computeroutput>jackbin.( ... )</computeroutput> to make
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a bin of a specified type. Square brackets make pipelines, and curly braces make
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threads. The default toplevel bin type is a pipeline, although putting the whole
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description within parentheses or braces can override this default.
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</para>
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</sect3>
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</sect2>
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</sect1>
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<sect1>
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<title><command>gst-inspect</command></title>
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<para>
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This is a tool to query a plugin or an element about its properties.
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</para>
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<para>
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To query the information about the element mad, you would specify:
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</para>
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<screen>
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gst-inspect mad
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</screen>
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<para>
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Below is the output of a query for the osssink element:
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</para>
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<screen>
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Factory Details:
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Long name: Audio Sink (OSS)
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Class: Sink/Audio
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Description: Output to a sound card via OSS
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Version: 0.3.3.1
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Author(s): Erik Walthinsen <omega@cse.ogi.edu>, Wim Taymans <wim.taymans@chello.be>
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Copyright: (C) 1999
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GObject
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+----GstObject
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+----GstElement
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+----GstOssSink
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Pad Templates:
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SINK template: 'sink'
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Availability: Always
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Capabilities:
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'osssink_sink':
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MIME type: 'audio/raw':
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format: String: int
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endianness: Integer: 1234
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width: List:
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Integer: 8
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Integer: 16
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depth: List:
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Integer: 8
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Integer: 16
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channels: Integer range: 1 - 2
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law: Integer: 0
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signed: List:
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Boolean: FALSE
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Boolean: TRUE
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rate: Integer range: 1000 - 48000
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Element Flags:
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GST_ELEMENT_THREADSUGGESTED
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Element Implementation:
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No loopfunc(), must be chain-based or not configured yet
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Has change_state() function: gst_osssink_change_state
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Has custom save_thyself() function: gst_element_save_thyself
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Has custom restore_thyself() function: gst_element_restore_thyself
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Clocking Interaction:
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element requires a clock
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element provides a clock: GstOssClock
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Pads:
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SINK: 'sink'
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Implementation:
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Has chainfunc(): 0x40056fc0
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Pad Template: 'sink'
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Element Arguments:
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name : String (Default "element")
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device : String (Default "/dev/dsp")
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mute : Boolean (Default false)
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format : Integer (Default 16)
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channels : Enum "GstAudiosinkChannels" (default 1)
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(0): Silence
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(1): Mono
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(2): Stereo
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frequency : Integer (Default 11025)
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fragment : Integer (Default 6)
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buffer-size : Integer (Default 4096)
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Element Signals:
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"handoff" : void user_function (GstOssSink* object,
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gpointer user_data);
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</screen>
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<para>
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To query the information about a plugin, you would do:
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</para>
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<screen>
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gst-inspect gstelements
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</screen>
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</sect1>
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</chapter>
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