Difference between revisions of "Gstreamer cheat sheet"

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== Network Streaming ==
== Encoding and Muxing ==
== Encoding and Muxing ==
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== Network Streaming ==
== Compositing ==
== Compositing ==

Revision as of 12:51, 20 June 2010

This page contains various shortcuts to achieving specific functionality using Gstreamer. These functionalities are mostly related to my Digital Video Transmission experiments. There is no easy to read "user manual" for gstreamer but the online the plugin documentation[1] often contains command line examples in addition to the API docs. Other sources of documentation:

  • The manual page for gst-launch
  • The gst-inspect tool
  • Online tutorials

The Gstreamer documentation is also available in Devhelp.

Video Test Source

To generate a test video stream use videotestsrc[2]:

 gst-launch videotestsrc ! ximagesink

Use the pattern property to select a specific pattern:

 gst-launch videotestsrc pattern=snow ! ximagesink

pattern can be both numeric [0,16] and symbolic. Some patterns can be adjusted using additional parameters.

To generate a test pattern of a given size and at a given rate a "caps filter" can be used:

 gst-launch videotestsrc ! video/x-raw-rgb, framerate=25/1, width=640, height=360 ! ximagesink

TODO: I'd like to add more about "caps filter" but I can not find any comprehensive documentation.

Webcam Capture

In its simplest form a v4l2src[3] can be connected directly to a video display sink:

 gst-launch v4l2src ! xvimagesink

This will grab the images at the highest possible resolution, which for my Logitech QuickCam Pro 9000 is 1600x1200. Adding a "caps filter" in between we can select the size and the desired frametrate:

 gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240,framerate=20/1 ! xvimagesink

If the supported framerates are not good use videorate[4] to either insert or drop frames. This can also be used to deliver a fixed framerate in case the framerate from the camera varies.

The "caps filter" is also used to select a specific pixel format. The Logitech QuickCam Pro 9000 supports MJPG, YUYV, RGB3, BGR3, YU12 and YV12. The pixel format in the "caps filter" can be specified using fourcc[5] labels:

 gst-launch v4l2src ! video/x-raw-yuv,format=\(fourcc\)YUY2,width=320,height=240 ! xvimagesink

YUY2 is the standard YUYV 4:2:2 pixel format and corresponds to the YUYV format on the Logitech QuickCam Pro 9000.

Resizing and Cropping


For quick cropping from 4:3 to 16:9, the aspectratiocrop[6] plugin can be used:

 gst-launch v4l2src ! video/x-raw-yuv,width=640,height=480,framerate=15/1 ! aspectratiocrop aspect-ratio=16/9 ! ffmpegcolorspace ! xvimagesink







Encoding and Muxing

Single Stream

Encode video H.264 using x264 and put it into MPEG-TS transport stream:

 gst-launch -e videotestsrc ! video/x-raw-yuv, framerate=25/1, width=640, height=360 ! x264enc ! flutsmux ! filesink location=test.ts

Note that it requires the Fluendo TS Muxer gst-fluendo-mpegmux for muxing and gst-fluendo-mpegdemux. We can use the playbin plugin to play the recorded video:

 gst-launch -v playbin uri=file:///path/to/test.ts

The -v option allows us to see which blocks gstreamer decides to use. In this case it will automatically select flutsdemux for demuxing the MPEG-TS and ffdec_h264 for decoding the H.264 video.

Multiple Streams


Decoding and Demuxing


Network Streaming



Picture in Picture



four videos combined into one video matrix

Text Overlay

The texoverlay[8] plugin can be used to add text to the video stream:

 gst-launch videotestsrc ! video/x-raw-yuv,width=640,height=480,framerate=15/1 ! textoverlay text="Hello" ! ffmpegcolorspace ! ximagesink

It has many options for text positioning and alignment. User can also specify font properties as a Pango font description string, e.g. "Sans Italic 24".

TODO: A few font description examples.

Time Overlay

Elapsed time can be added using the timeoverlay[9] plugin:

 gst-launch videotestsrc ! timeoverlay ! xvimagesink

Timeoverlay inherits the properties of textoverlay so the text properties can be set using the same properties:

 gst-launch videotestsrc ! timeoverlay halign=right valign=bottom text="Stream time:" shaded-background=true ! xvimagesink

Alternatively, cairotimeoverlay[10] can be used but it doesn't seem to have any properties:

 gst-launch videotestsrc ! cairotimeoverlay ! xvimagesink

Instead of elapsed time, the system date and time can be added using the clockoverlay[11] plugin:

 gst-launch videotestsrc ! clockoverlay ! xvimagesink

Clockloverlay also inherits the properties of textoverlay. In addition to that clockoverlay also allows setting the time format:

 gst-launch videotestsrc ! clockoverlay halign=right valign=bottom shaded-background=true time-format="%Y.%m.%D" ! ffmpegcolorspace ! ximagesink

Complete Examples



  1. Gstreamer documentation http://gstreamer.freedesktop.org/documentation/
  2. GStreamer Base Plugins 0.10 Plugins Reference Manual – videotestsrc
  3. GStreamer Good Plugins 0.10 Plugins Reference Manual – v4l2src
  4. GStreamer Base Plugins 0.10 Plugins Reference Manual – videorate
  5. FOURCC websiteYUV formats
  6. GStreamer Good Plugins 0.10 Plugins Reference Manual – aspectratiocrop
  7. GStreamer Good Plugins 0.10 Plugins Reference Manual – videomixer
  8. GStreamer Base Plugins 0.10 Plugins Reference Manual – textoverlay
  9. GStreamer Base Plugins 0.10 Plugins Reference Manual – timeoverlay
  10. GStreamer Good Plugins 0.10 Plugins Reference Manual – cairotimeoverlay
  11. GStreamer Base Plugins 0.10 Plugins Reference Manual - clockoverlay