1 # Basic tutorial 10: GStreamer tools
5 GStreamer comes with a set of tools which range from handy to
6 absolutely essential. There is no code in this tutorial, just sit back
7 and relax, and we will teach you:
9 - How to build and run GStreamer pipelines from the command line,
10 without using C at all!
11 - How to find out what GStreamer elements you have available and their
13 - How to discover the internal structure of media files.
17 These tools are available in the bin directory of the GStreamer
18 binaries. You need to move to this directory to execute them, because
19 it is not added to the system’s `PATH` environment variable (to avoid
20 polluting it too much).
22 Just open a terminal (or console window) and go to the `bin` directory
23 of your GStreamer installation (Read again the [Installing
24 GStreamer](installing/index.md) section to find our where this is),
25 and you are ready to start typing the commands given in this tutorial.
28 > ![Information](images/icons/emoticons/information.png)
30 > On Linux, you should use the GStreamer version installed with your
31 > distribution, the tools should be installed with a package named `gstreamer1`
32 > on Fedora style distributions, or `gstreamer1.0-tools` on Debian/Ubuntu style
35 In order to allow for multiple versions of GStreamer to coexists in the
36 same system, these tools are versioned, this is, a GStreamer version
37 number is appended to their name. This version is based on
38 GStreamer 1.0, so the tools are called `gst-launch-1.0`,
39 `gst-inspect-1.0` and `gst-discoverer-1.0`
43 This tool accepts a textual description of a pipeline, instantiates it,
44 and sets it to the PLAYING state. It allows you to quickly check if a
45 given pipeline works, before going through the actual implementation
46 using GStreamer API calls.
48 Bear in mind that it can only create simple pipelines. In particular, it
49 can only simulate the interaction of the pipeline with the application
50 up to a certain level. In any case, it is extremely handy to test
51 pipelines quickly, and is used by GStreamer developers around the world
54 Please note that `gst-launch-1.0` is primarily a debugging tool for
55 developers. You should not build applications on top of it. Instead, use
56 the `gst_parse_launch()` function of the GStreamer API as an easy way to
57 construct pipelines from pipeline descriptions.
59 Although the rules to construct pipeline descriptions are very simple,
60 the concatenation of multiple elements can quickly make such
61 descriptions resemble black magic. Fear not, for everyone learns the
62 `gst-launch-1.0` syntax, eventually.
64 The command line for gst-launch-1.0 consists of a list of options followed
65 by a PIPELINE-DESCRIPTION. Some simplified instructions are given next,
66 se the complete documentation at [the reference page](tools/gst-launch.md)
71 In simple form, a PIPELINE-DESCRIPTION is a list of element types
72 separated by exclamation marks (!). Go ahead and type in the following
76 gst-launch-1.0 videotestsrc ! videoconvert ! autovideosink
79 You should see a windows with an animated video pattern. Use CTRL+C on
80 the terminal to stop the program.
82 This instantiates a new element of type `videotestsrc` (an element which
83 generates a sample video pattern), an `videoconvert` (an element
84 which does raw video format conversion, making sure other elements can
85 understand each other), and an `autovideosink` (a window to which video
86 is rendered). Then, GStreamer tries to link the output of each element
87 to the input of the element appearing on its right in the description.
88 If more than one input or output Pad is available, the Pad Caps are used
89 to find two compatible Pads.
93 Properties may be appended to elements, in the form
94 *property=value *(multiple properties can be specified, separated by
95 spaces). Use the `gst-inspect-1.0` tool (explained next) to find out the
96 available properties for an
100 gst-launch-1.0 videotestsrc pattern=11 ! videoconvert ! autovideosink
103 You should see a static video pattern, made of circles.
107 Elements can be named using the `name` property, in this way complex
108 pipelines involving branches can be created. Names allow linking to
109 elements created previously in the description, and are indispensable to
110 use elements with multiple output pads, like demuxers or tees, for
113 Named elements are referred to using their name followed by a
117 gst-launch-1.0 videotestsrc ! videoconvert ! tee name=t ! queue ! autovideosink t. ! queue ! autovideosink
120 You should see two video windows, showing the same sample video pattern.
121 If you see only one, try to move it, since it is probably on top of the
124 This example instantiates a `videotestsrc`, linked to a
125 `videoconvert`, linked to a `tee` (Remember from [](tutorials/basic/multithreading-and-pad-availability.md) that
126 a `tee` copies to each of its output pads everything coming through its
127 input pad). The `tee` is named simply ‘t’ (using the `name` property)
128 and then linked to a `queue` and an `autovideosink`. The same `tee` is
129 referred to using ‘t.’ (mind the dot) and then linked to a second
130 `queue` and a second `autovideosink`.
132 To learn why the queues are necessary read [](tutorials/basic/multithreading-and-pad-availability.md).
136 Instead of letting GStreamer choose which Pad to use when linking two
137 elements, you may want to specify the Pads directly. You can do this by
138 adding a dot plus the Pad name after the name of the element (it must be
139 a named element). Learn the names of the Pads of an element by using
140 the `gst-inspect-1.0` tool.
142 This is useful, for example, when you want to retrieve one particular
147 gst-launch-1.0 souphttpsrc location=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! matroskademux name=d d.video_00 ! matroskamux ! filesink location=sintel_video.mkv
150 This fetches a media file from the internet using `souphttpsrc`, which
151 is in webm format (a special kind of Matroska container, see [](tutorials/basic/concepts.md)). We
152 then open the container using `matroskademux`. This media contains both
153 audio and video, so `matroskademux` will create two output Pads, named
154 `video_00` and `audio_00`. We link `video_00` to a `matroskamux` element
155 to re-pack the video stream into a new container, and finally link it to
156 a `filesink`, which will write the stream into a file named
157 "sintel\_video.mkv" (the `location` property specifies the name of the
160 All in all, we took a webm file, stripped it of audio, and generated a
161 new matroska file with the video. If we wanted to keep only the
165 gst-launch-1.0 souphttpsrc location=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! matroskademux name=d d.audio_00 ! vorbisparse ! matroskamux ! filesink location=sintel_audio.mka
168 The `vorbisparse` element is required to extract some information from
169 the stream and put it in the Pad Caps, so the next element,
170 `matroskamux`, knows how to deal with the stream. In the case of video
171 this was not necessary, because `matroskademux` already extracted this
172 information and added it to the Caps.
174 Note that in the above two examples no media has been decoded or played.
175 We have just moved from one container to another (demultiplexing and
176 re-multiplexing again).
180 When an element has more than one output pad, it might happen that the
181 link to the next element is ambiguous: the next element may have more
182 than one compatible input pad, or its input pad may be compatible with
183 the Pad Caps of all the output pads. In these cases GStreamer will link
184 using the first pad that is available, which pretty much amounts to
185 saying that GStreamer will choose one output pad at random.
187 Consider the following
191 gst-launch-1.0 souphttpsrc location=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! matroskademux ! filesink location=test
194 This is the same media file and demuxer as in the previous example. The
195 input Pad Caps of `filesink` are `ANY`, meaning that it can accept any
196 kind of media. Which one of the two output pads of `matroskademux` will
197 be linked against the filesink? `video_00` or `audio_00`? You cannot
200 You can remove this ambiguity, though, by using named pads, as in the
201 previous sub-section, or by using **Caps
205 gst-launch-1.0 souphttpsrc location=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! matroskademux ! video/x-vp8 ! matroskamux ! filesink location=sintel_video.mkv
208 A Caps Filter behaves like a pass-through element which does nothing and
209 only accepts media with the given Caps, effectively resolving the
210 ambiguity. In this example, between `matroskademux` and `matroskamux` we
211 added a `video/x-vp8` Caps Filter to specify that we are interested in
212 the output pad of `matroskademux` which can produce this kind of video.
214 To find out the Caps an element accepts and produces, use the
215 `gst-inspect-1.0` tool. To find out the Caps contained in a particular file,
216 use the `gst-discoverer-1.0` tool. To find out the Caps an element is
217 producing for a particular pipeline, run `gst-launch-1.0` as usual, with the
218 `–v` option to print Caps information.
222 Play a media file using `playbin` (as in [](tutorials/basic/hello-world.md)):
225 gst-launch-1.0 playbin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm
228 A fully operation playback pipeline, with audio and video (more or less
229 the same pipeline that `playbin` will create
233 gst-launch-1.0 souphttpsrc location=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! matroskademux name=d ! queue ! vp8dec ! videoconvert ! autovideosink d. ! queue ! vorbisdec ! audioconvert ! audioresample ! autoaudiosink
236 A transcoding pipeline, which opens the webm container and decodes both
237 streams (via uridecodebin), then re-encodes the audio and video branches
238 with a different codec, and puts them back together in an Ogg container
239 (just for the sake of
243 gst-launch-1.0 uridecodebin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm name=d ! queue ! theoraenc ! oggmux name=m ! filesink location=sintel.ogg d. ! queue ! audioconvert ! audioresample ! flacenc ! m.
246 A rescaling pipeline. The `videoscale` element performs a rescaling
247 operation whenever the frame size is different in the input and the
248 output caps. The output caps are set by the Caps Filter to
252 gst-launch-1.0 uridecodebin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm ! queue ! videoscale ! video/x-raw-yuv,width=320,height=200 ! videoconvert ! autovideosink
255 This short description of `gst-launch-1.0` should be enough to get you
256 started. Remember that you have the [complete documentation available
257 here](tools/gst-launch.md).
261 This tool has three modes of operation:
263 - Without arguments, it lists all available elements types, this is,
264 the types you can use to instantiate new elements.
265 - With a file name as an argument, it treats the file as a GStreamer
266 plugin, tries to open it, and lists all the elements described
268 - With a GStreamer element name as an argument, it lists all
269 information regarding that element.
271 Let's see an example of the third mode:
274 gst-inspect-1.0 vp8dec
278 Long-name On2 VP8 Decoder
279 Klass Codec/Decoder/Video
280 Description Decode VP8 video streams
281 Author David Schleef <ds@entropywave.com>, Sebastian Dröge <sebastian.droege@collabora.co.uk>
285 Description VP8 plugin
286 Filename /usr/lib64/gstreamer-1.0/libgstvpx.so
289 Source module gst-plugins-good
290 Source release date 2016-04-14
291 Binary package Fedora GStreamer-plugins-good package
292 Origin URL http://download.fedoraproject.org
295 +----GInitiallyUnowned
302 SINK template: 'sink'
312 width: [ 1, 2147483647 ]
313 height: [ 1, 2147483647 ]
314 framerate: [ 0/1, 2147483647/1 ]
320 Element Implementation:
321 Has change_state() function: gst_video_decoder_change_state
323 Element has no clocking capabilities.
324 Element has no URI handling capabilities.
333 name : The name of the object
334 flags: readable, writable
335 String. Default: "vp8dec0"
336 parent : The parent of the object
337 flags: readable, writable
338 Object of type "GstObject"
339 post-processing : Enable post processing
340 flags: readable, writable
341 Boolean. Default: false
342 post-processing-flags: Flags to control post processing
343 flags: readable, writable
344 Flags "GstVP8DecPostProcessingFlags" Default: 0x00000403, "mfqe+demacroblock+deblock"
345 (0x00000001): deblock - Deblock
346 (0x00000002): demacroblock - Demacroblock
347 (0x00000004): addnoise - Add noise
348 (0x00000400): mfqe - Multi-frame quality enhancement
349 deblocking-level : Deblocking level
350 flags: readable, writable
351 Unsigned Integer. Range: 0 - 16 Default: 4
352 noise-level : Noise level
353 flags: readable, writable
354 Unsigned Integer. Range: 0 - 16 Default: 0
355 threads : Maximum number of decoding threads
356 flags: readable, writable
357 Unsigned Integer. Range: 1 - 16 Default: 0
360 The most relevant sections are:
362 - Pad Templates: This lists all the kinds of Pads this
363 element can have, along with their capabilities. This is where you
364 look to find out if an element can link with another one. In this
365 case, it has only one sink pad template, accepting only
366 `video/x-vp8` (encoded video data in VP8 format) and only one source
367 pad template, producing `video/x-raw` (decoded video data).
368 - Element Properties: This lists the properties of the
369 element, along with their type and accepted values.
371 For more information, you can check the [documentation
372 page](tools/gst-inspect.md) of `gst-inspect-1.0`.
374 ## `gst-discoverer-1.0`
376 This tool is a wrapper around the `GstDiscoverer` object shown in [](tutorials/basic/media-information-gathering.md).
377 It accepts a URI from the command line and prints all information
378 regarding the media that GStreamer can extract. It is useful to find out
379 what container and codecs have been used to produce the media, and
380 therefore what elements you need to put in a pipeline to play it.
382 Use `gst-discoverer-1.0 --help` to obtain the list of available options,
383 which basically control the amount of verbosity of the output.
389 gst-discoverer-1.0 https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm -v
391 Analyzing https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm
392 Done discovering https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm
394 container: video/webm
395 audio: audio/x-vorbis, channels=(int)2, rate=(int)48000
397 audio/x-vorbis, channels=(int)2, rate=(int)48000
407 taglist, language-code=(string)en, container-format=(string)Matroska, audio-codec=(string)Vorbis, application-name=(string)ffmpeg2theora-0.24, encoder=(string)"Xiph.Org\ libVorbis\ I\ 20090709", encoder-version=(uint)0, nominal-bitrate=(uint)80000, bitrate=(uint)80000;
408 video: video/x-vp8, width=(int)854, height=(int)480, framerate=(fraction)25/1
410 video/x-vp8, width=(int)854, height=(int)480, framerate=(fraction)25/1
417 Pixel aspect ratio: 1/1
422 taglist, video-codec=(string)"VP8\ video", container-format=(string)Matroska;
425 Duration: 0:00:52.250000000
428 video codec: VP8 video
430 container format: Matroska
431 application name: ffmpeg2theora-0.24
432 encoder: Xiph.Org libVorbis I 20090709
435 nominal bitrate: 80000
441 This tutorial has shown:
443 - How to build and run GStreamer pipelines from the command line using
444 the `gst-launch-1.0` tool.
445 - How to find out what GStreamer elements you have available and their
446 capabilities, using the `gst-inspect-1.0` tool.
447 - How to discover the internal structure of media files, using
448 `gst-discoverer-1.0`.
450 It has been a pleasure having you here, and see you soon!