gstreamer/docs/manual/appendix-programs.xml
Sebastian Rasmussen 4cf6a6e086 tests: Add missing unrefs of objects after use
Unreffing the objects returned by gst_bin_get_by_name() and
gst_pipeline_get_use() were missing in several tests, so add these.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=734345
2014-08-06 13:47:11 +02:00

342 lines
13 KiB
XML

<chapter id="chapter-programs">
<title>Programs</title>
<para>
</para>
<sect1 id="section-programs-gst-launch">
<title><command>gst-launch</command></title>
<para>
This is a tool that will construct pipelines based on a command-line
syntax.
</para>
<para>
A simple commandline looks like:
<screen>
gst-launch filesrc location=hello.mp3 ! mad ! audioresample ! osssink
</screen>
A more complex pipeline looks like:
<screen>
gst-launch filesrc location=redpill.vob ! dvddemux name=demux \
demux.audio_00 ! queue ! a52dec ! audioconvert ! audioresample ! osssink \
demux.video_00 ! queue ! mpeg2dec ! videoconvert ! xvimagesink
</screen>
</para>
<para>
You can also use the parser in you own
code. <application>GStreamer</application> provides a function
gst_parse_launch () that you can use to construct a pipeline.
The following program lets you create an MP3 pipeline using the
gst_parse_launch () function:
</para>
<programlisting>
#include &lt;gst/gst.h&gt;
int
main (int argc, char *argv[])
{
GstElement *pipeline;
GstElement *filesrc;
GstMessage *msg;
GstBus *bus;
GError *error = NULL;
gst_init (&amp;argc, &amp;argv);
if (argc != 2) {
g_print ("usage: %s &lt;filename&gt;\n", argv[0]);
return -1;
}
pipeline = gst_parse_launch ("filesrc name=my_filesrc ! mad ! osssink", &amp;error);
if (!pipeline) {
g_print ("Parse error: %s\n", error->message);
exit (1);
}
filesrc = gst_bin_get_by_name (GST_BIN (pipeline), "my_filesrc");
g_object_set (filesrc, "location", argv[1], NULL);
g_object_unref (filesrc);
gst_element_set_state (pipeline, GST_STATE_PLAYING);
bus = gst_element_get_bus (pipeline);
/* wait until we either get an EOS or an ERROR message. Note that in a real
* program you would probably not use gst_bus_poll(), but rather set up an
* async signal watch on the bus and run a main loop and connect to the
* bus's signals to catch certain messages or all messages */
msg = gst_bus_poll (bus, GST_MESSAGE_EOS | GST_MESSAGE_ERROR, -1);
switch (GST_MESSAGE_TYPE (msg)) {
case GST_MESSAGE_EOS: {
g_print ("EOS\n");
break;
}
case GST_MESSAGE_ERROR: {
GError *err = NULL; /* error to show to users */
gchar *dbg = NULL; /* additional debug string for developers */
gst_message_parse_error (msg, &amp;err, &amp;dbg);
if (err) {
g_printerr ("ERROR: %s\n", err-&gt;message);
g_error_free (err);
}
if (dbg) {
g_printerr ("[Debug details: %s]\n", dbg);
g_free (dbg);
}
}
default:
g_printerr ("Unexpected message of type %d", GST_MESSAGE_TYPE (msg));
break;
}
gst_message_unref (msg);
gst_element_set_state (pipeline, GST_STATE_NULL);
gst_object_unref (pipeline);
gst_object_unref (bus);
return 0;
}
</programlisting>
<para>
Note how we can retrieve the filesrc element from the constructed bin using the
element name.
</para>
<sect2>
<title>Grammar Reference</title>
<para>
The <command>gst-launch</command> syntax is processed by a flex/bison parser. This section
is intended to provide a full specification of the grammar; any deviations from this
specification is considered a bug.
</para>
<sect3>
<title>Elements</title>
<screen>
... mad ...
</screen>
<para>
A bare identifier (a string beginning with a letter and containing
only letters, numbers, dashes, underscores, percent signs, or colons)
will create an element from a given element factory. In this example,
an instance of the "mad" MP3 decoding plugin will be created.
</para>
</sect3>
<sect3>
<title>Links</title>
<screen>
... !sink ...
</screen>
<para>
An exclamation point, optionally having a qualified pad name (an the name of the pad,
optionally preceded by the name of the element) on both sides, will link two pads. If
the source pad is not specified, a source pad from the immediately preceding element
will be automatically chosen. If the sink pad is not specified, a sink pad from the next
element to be constructed will be chosen. An attempt will be made to find compatible
pads. Pad names may be preceded by an element name, as in
<computeroutput>my_element_name.sink_pad</computeroutput>.
</para>
</sect3>
<sect3>
<title>Properties</title>
<screen>
... location="http://gstreamer.net" ...
</screen>
<para>
The name of a property, optionally qualified with an element name, and a value,
separated by an equals sign, will set a property on an element. If the element is not
specified, the previous element is assumed. Strings can optionally be enclosed in
quotation marks. Characters in strings may be escaped with the backtick
(<literal>\</literal>). If the right-hand side is all digits, it is considered to be an
integer. If it is all digits and a decimal point, it is a double. If it is "true",
"false", "TRUE", or "FALSE" it is considered to be boolean. Otherwise, it is parsed as a
string. The type of the property is determined later on in the parsing, and the value is
converted to the target type. This conversion is not guaranteed to work, it relies on
the g_value_convert routines. No error message will be displayed on an invalid
conversion, due to limitations in the value convert API.
</para>
</sect3>
<sect3>
<title>Bins, Threads, and Pipelines</title>
<screen>
( ... )
</screen>
<para>
A pipeline description between parentheses is placed into a bin. The open paren may be
preceded by a type name, as in <computeroutput>jackbin.( ... )</computeroutput> to make
a bin of a specified type. Square brackets make pipelines, and curly braces make
threads. The default toplevel bin type is a pipeline, although putting the whole
description within parentheses or braces can override this default.
</para>
</sect3>
</sect2>
</sect1>
<sect1 id="section-programs-gst-inspect">
<title><command>gst-inspect</command></title>
<para>
This is a tool to query a plugin or an element about its properties.
</para>
<para>
To query the information about the element mad, you would specify:
</para>
<screen>
gst-inspect mad
</screen>
<para>
Below is the output of a query for the osssink element:
</para>
<screen>
<![CDATA[
Factory Details:
Rank: secondary (128)
Long-name: Audio Sink (OSS)
Klass: Sink/Audio
Description: Output to a sound card via OSS
Author: Erik Walthinsen <omega@cse.ogi.edu>, Wim Taymans <wim.taymans@chello.be>
Plugin Details:
Name: ossaudio
Description: OSS (Open Sound System) support for GStreamer
Filename: /home/wim/gst/head/gst-plugins-good/sys/oss/.libs/libgstossaudio.so
Version: 1.0.0.1
License: LGPL
Source module: gst-plugins-good
Source release date: 2012-09-25 12:52 (UTC)
Binary package: GStreamer Good Plug-ins git
Origin URL: Unknown package origin
GObject
+----GInitiallyUnowned
+----GstObject
+----GstElement
+----GstBaseSink
+----GstAudioBaseSink
+----GstAudioSink
+----GstOssSink
Pad Templates:
SINK template: 'sink'
Availability: Always
Capabilities:
audio/x-raw
format: { S16LE, U16LE, S8, U8 }
layout: interleaved
rate: [ 1, 2147483647 ]
channels: 1
audio/x-raw
format: { S16LE, U16LE, S8, U8 }
layout: interleaved
rate: [ 1, 2147483647 ]
channels: 2
channel-mask: 0x0000000000000003
Element Flags:
no flags set
Element Implementation:
Has change_state() function: gst_audio_base_sink_change_state
Clocking Interaction:
element is supposed to provide a clock but returned NULL
Element has no indexing capabilities.
Element has no URI handling capabilities.
Pads:
SINK: 'sink'
Implementation:
Has chainfunc(): gst_base_sink_chain
Has custom eventfunc(): gst_base_sink_event
Has custom queryfunc(): gst_base_sink_sink_query
Has custom iterintlinkfunc(): gst_pad_iterate_internal_links_default
Pad Template: 'sink'
Element Properties:
name : The name of the object
flags: readable, writable
String. Default: "osssink0"
parent : The parent of the object
flags: readable, writable
Object of type "GstObject"
sync : Sync on the clock
flags: readable, writable
Boolean. Default: true
max-lateness : Maximum number of nanoseconds that a buffer can be late before it is dropped (-1 unlimited)
flags: readable, writable
Integer64. Range: -1 - 9223372036854775807 Default: -1
qos : Generate Quality-of-Service events upstream
flags: readable, writable
Boolean. Default: false
async : Go asynchronously to PAUSED
flags: readable, writable
Boolean. Default: true
ts-offset : Timestamp offset in nanoseconds
flags: readable, writable
Integer64. Range: -9223372036854775808 - 9223372036854775807 Default: 0
enable-last-sample : Enable the last-sample property
flags: readable, writable
Boolean. Default: false
last-sample : The last sample received in the sink
flags: readable
Boxed pointer of type "GstSample"
blocksize : Size in bytes to pull per buffer (0 = default)
flags: readable, writable
Unsigned Integer. Range: 0 - 4294967295 Default: 4096
render-delay : Additional render delay of the sink in nanoseconds
flags: readable, writable
Unsigned Integer64. Range: 0 - 18446744073709551615 Default: 0
throttle-time : The time to keep between rendered buffers
flags: readable, writable
Unsigned Integer64. Range: 0 - 18446744073709551615 Default: 0
buffer-time : Size of audio buffer in microseconds, this is the minimum latency that the sink reports
flags: readable, writable
Integer64. Range: 1 - 9223372036854775807 Default: 200000
latency-time : The minimum amount of data to write in each iteration in microseconds
flags: readable, writable
Integer64. Range: 1 - 9223372036854775807 Default: 10000
provide-clock : Provide a clock to be used as the global pipeline clock
flags: readable, writable
Boolean. Default: true
slave-method : Algorithm to use to match the rate of the masterclock
flags: readable, writable
Enum "GstAudioBaseSinkSlaveMethod" Default: 1, "skew"
(0): resample - GST_AUDIO_BASE_SINK_SLAVE_RESAMPLE
(1): skew - GST_AUDIO_BASE_SINK_SLAVE_SKEW
(2): none - GST_AUDIO_BASE_SINK_SLAVE_NONE
can-activate-pull : Allow pull-based scheduling
flags: readable, writable
Boolean. Default: false
alignment-threshold : Timestamp alignment threshold in nanoseconds
flags: readable, writable
Unsigned Integer64. Range: 1 - 18446744073709551614 Default: 40000000
drift-tolerance : Tolerance for clock drift in microseconds
flags: readable, writable
Integer64. Range: 1 - 9223372036854775807 Default: 40000
discont-wait : Window of time in nanoseconds to wait before creating a discontinuity
flags: readable, writable
Unsigned Integer64. Range: 0 - 18446744073709551614 Default: 1000000000
device : OSS device (usually /dev/dspN)
flags: readable, writable
String. Default: "/dev/dsp"
]]>
</screen>
<para>
To query the information about a plugin, you would do:
</para>
<screen>
gst-inspect gstelements
</screen>
</sect1>
</chapter>