Update
This commit is contained in:
Akkariin Meiko
@@ -0,0 +1,334 @@
|
||||
---
|
||||
title: Programs
|
||||
...
|
||||
|
||||
# Programs
|
||||
|
||||
## `gst-launch`
|
||||
|
||||
This is a tool that will construct pipelines based on a command-line
|
||||
syntax.
|
||||
|
||||
A simple commandline looks like:
|
||||
|
||||
```
|
||||
gst-launch filesrc location=hello.mp3 ! mad ! audioresample ! osssink
|
||||
|
||||
```
|
||||
|
||||
A more complex pipeline looks like:
|
||||
|
||||
```
|
||||
gst-launch filesrc location=redpill.vob ! dvddemux name=demux \
|
||||
demux.audio_00 ! queue ! a52dec ! audioconvert ! audioresample ! osssink \
|
||||
demux.video_00 ! queue ! mpeg2dec ! videoconvert ! xvimagesink
|
||||
|
||||
```
|
||||
|
||||
You can also use the parser in you own code. GStreamer 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:
|
||||
|
||||
``` c
|
||||
#include <gst/gst.h>
|
||||
|
||||
int
|
||||
main (int argc, char *argv[])
|
||||
{
|
||||
GstElement *pipeline;
|
||||
GstElement *filesrc;
|
||||
GstMessage *msg;
|
||||
GstBus *bus;
|
||||
GError *error = NULL;
|
||||
|
||||
gst_init (&argc, &argv);
|
||||
|
||||
if (argc != 2) {
|
||||
g_print ("usage: %s <filename>\n", argv[0]);
|
||||
return -1;
|
||||
}
|
||||
|
||||
pipeline = gst_parse_launch ("filesrc name=my_filesrc ! mad ! osssink", &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, &err, &dbg);
|
||||
if (err) {
|
||||
g_printerr ("ERROR: %s\n", err->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;
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Note how we can retrieve the filesrc element from the constructed bin
|
||||
using the element name.
|
||||
|
||||
### Grammar Reference
|
||||
|
||||
The `gst-launch` 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.
|
||||
|
||||
#### Elements
|
||||
|
||||
```
|
||||
... mad ...
|
||||
|
||||
```
|
||||
|
||||
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.
|
||||
|
||||
#### Links
|
||||
|
||||
```
|
||||
... !sink ...
|
||||
|
||||
```
|
||||
|
||||
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
|
||||
`my_element_name.sink_pad`.
|
||||
|
||||
#### Properties
|
||||
|
||||
```
|
||||
... location="http://gstreamer.net" ...
|
||||
|
||||
```
|
||||
|
||||
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 (`\`). 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.
|
||||
|
||||
#### Bins, Threads, and Pipelines
|
||||
|
||||
```
|
||||
( ... )
|
||||
|
||||
```
|
||||
|
||||
A pipeline description between parentheses is placed into a bin. The
|
||||
open paren may be preceded by a type name, as in `jackbin.( ... )` 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.
|
||||
|
||||
## `gst-inspect`
|
||||
|
||||
This is a tool to query a plugin or an element about its properties.
|
||||
|
||||
To query the information about the element mad, you would specify:
|
||||
|
||||
```
|
||||
gst-inspect mad
|
||||
|
||||
```
|
||||
|
||||
Below is the output of a query for the osssink element:
|
||||
|
||||
```
|
||||
|
||||
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"
|
||||
|
||||
|
||||
```
|
||||
|
||||
To query the information about a plugin, you would do:
|
||||
|
||||
```
|
||||
gst-inspect gstelements
|
||||
|
||||
```
|
||||
Reference in New Issue
Block a user