Revision as of 00:47, 3 October 2013 by Quozl (Talk | contribs)
Jump to: navigation, search

GStreamer is our multimedia framework library.



GStreamer is a library that supports multimedia, ranging from playback to complex mixing and processing.

Adding codecs

This section describes third-party software that does not meet the OLPC standards for software freedom. The use of such software is unsupported; OLPC does not endorse or encourage its use.

On the XO laptop, start Terminal and paste this:[1]

sudo yum localinstall -y --nogpgcheck \$(rpm -E %fedora).noarch.rpm \$(rpm -E %fedora).noarch.rpm && \
sudo yum install -y gstreamer-plugins-ugly gstreamer-plugins-bad gstreamer-ffmpeg

When the prompt reappears, with "Complete!" above the prompt, it is ready to use. You may need to restart any activity using GStreamer, once.

These instructions have been tested for releases 10.1.2, 12.1.0 and 13.2.0.

For more information, see:

See also Fluendo mp3 decoder instructions.

The rest of this page is oriented towards developers using GStreamer.

Getting started programming

Getting started with GStreamer with Python



  • Have to script v4l2 via gstreamer to capture a single frame from the camera. See sugar/shell/intro/ for sample code
  • Try this from the command line: gst-launch-0.10 v4l2src ! ffmpegcolorspace ! pngenc ! filesink location=foo.png
  • See also: Programming the camera
  • You can simulate this hardware via a file source in gstreamer

Camera-as-video-camera (v4l2)

  • Is a regular v4l2 device available via gstreamer (gst module)
    • If you do not have hardware, you can simulate the camera interactively with an regular v4l2 source (many cheap web-cams provide this type of source)
    • For test-driven development, you can use any gstreamer source (such as a regular file), hooking up your code to use a file source instead of a v4l2src
  • Try this from a terminal in the developer console: gst-launch-0.10 v4l2src ! ximagesink (The image will appear behind the developer console window so you'll need to move the window aside. In addition, it will have strange colors, since you are displaying the YCrCb colorspace as though it is RGB data. Use gst-launch-0.10 v4l2src ! ffmpegcolorspace ! ximagesink to run slowly and get the right colors.)
  • See also: Programming the camera
  • You can simulate this hardware via a file source in gstreamer

GStreamer 101


v4l2src can always be replaced by videotestsrc, and alsasrc by audiotestsrc.

Beginning of a normal video pipeline:

v4l2src ! queue ! videorate ! video/x-raw-yuv,framerate=15/1 ! videoscale ! video/x-raw-yuv,width=160,height=120 ! ...

Beginning of a normal audio pipeline:

alsasrc ! audio/x-raw-int,rate=8000,channels=1,depth=8 ! ...

Video encoding:

... ! ffmpegcolorspace ! theoraenc ! ...

Audio encoding:

... ! audioconvert ! vorbisenc ! ...

Video output:

... ! ffmpegcolorspace ! videoscale ! ximagesink

Audio output:

... ! audioconvert ! alsasink sync=false


... ! fdsink fd=1

Encode video+audio as ogg:

v4l2src ! queue ! ffmpegcolorspace ! theoraenc ! queue ! \
  oggmux name=mux  alsasrc ! queue ! audioconvert ! vorbisenc ! queue ! mux. mux. ! queue ! ...

A long version of videotestsrc ! ximagesink:

videotestsrc ! theoraenc ! oggmux ! oggdemux ! theoradec ! ffmpegcolorspace ! videoscale ! ximagesink

A long version of videotestsrc ! ximagesink &; audiotestsrc ! alsasink:

videotestsrc ! ffmpegcolorspace ! theoraenc ! queue ! \
  oggmux name=mux audiotestsrc ! audioconvert ! vorbisenc ! queue ! mux. mux. ! queue ! \
  oggdemux name=demux ! queue ! theoradec ! ffmpegcolorspace ! \
    ximagesink demux. ! queue ! vorbisdec ! audioconvert ! alsasink
Hangs on current fc6. MitchellNCharity 17:43, 12 June 2007 (EDT)

Live video streaming to an icecast server:

v4l2src ! ffmpegcolorspace ! videoscale ! video/x-raw-yuv,width=320,height=240 ! theoraenc quality=16 ! oggmux ! shout2send ip= port=8000 password=hackme mount=olpc.ogg

Live streaming to an icecast server:

v4l2src ! queue ! ffmpegcolorspace ! theoraenc quality=16 ! queue ! oggmux name=mux  alsasrc ! audio/x-raw-int,rate=8000,channels=1,depth=8 ! queue ! audioconvert ! vorbisenc ! queue ! mux. mux. ! \
  queue ! shout2send ip=... port=... password=... mount=/whatever.ogg

Time lapse photography (1 frame every 30 seconds):

gst-launch v4l2src ! videorate ! video/x-raw-yuv,width=640,height=480,framerate=\(fraction\)1/30 ! ffmpegcolorspace ! jpegenc ! multipartmux ! filesink location=lapse1.mjpeg

press ctrl-c to stop


gst-launch filesrc location=lapse1.mjpeg ! multipartdemux ! jpegdec ! ffmpegcolorspace ! autovideosink



The video coming raw out of v4l2src is color formatted YUYV. That is, there are 4 bytes per 2 pixels. The first 8 bit Y represents the luma (brightness) of the first pixel, the second 8 bit Y is the brightness of the second, the 8 bit U is the blue chrominance of both pixels, and the 8 bit V is the red chrominance of both.

video size, framerate, and theoraenc quality

audio encoding used wav rather than vorbis. Why?



Video characteristics:

Audio characteristics:

File I/O:

Video sources:

Audio sources:

Coding video:

Coding audio:


Outputing video:

Outputting audio:

Not sure about:

Sending ogg to an icecast streaming server:

... ! shout2send ip=... port=... password=... mount=/whatever.ogg
gst-launch ... ! fdsink | oggfwd host port password mount
Regretabbly, it appears fc6, and thus olpc, does not include shout2send in gst-plugins-good-plugins. Nor does it have rpms for oggfwd, or other possible alternatives. You can grab a random binary of oggfwd from it's site, or compile shout2send from source. :( MitchellNCharity 17:43, 12 June 2007 (EDT)
Correction, shout2send is on the olpc. oggfwd is not. --Damonkohler 23:14, 13 September 2007 (EDT)

Doing live streaming video from an xo


xo sending video:

gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240,framerate=\(fraction\)5/1 ! ffmpegcolorspace ! jpegenc ! multipartmux ! tcpserversink host= port=5000

xo recieving video:

gst-launch tcpclientsrc host= port=5001 ! multipartdemux ! jpegdec ! autovideosink


xo sending video:

gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240,framerate=\(fraction\)2/1 ! ffmpegcolorspace ! smokeenc keyframe=8 qmax=40 ! udpsink host= port=5000

xo receiving video:

gst-launch udpsrc port=5000 ! smokedec ! autovideosink

Method3 Video+Audio

Sending XO:

gst-launch v4l2src ! queue ! video/x-raw-yuv,width=320,height=240,framerate=\(fraction\)4/1 ! videorate ! videoscale ! ffmpegcolorspace ! queue ! smokeenc ! queue ! udpsink host= port=5000 alsasrc ! queue ! audio/x-raw-int,rate=8000,channels=1,depth=8 ! audioconvert ! speexenc ! queue ! tcpserversink host= port=5001

Receiving XO:

gst-launch-0.10 udpsrc port=5000 ! queue ! smokedec ! queue ! autovideosink tcpclientsrc host= port=5001 ! queue ! speexdec ! queue ! alsasink sync=false

Section TODO

  • Fill in blank sections.
  • Include snapshot recipes.
  • Discuss python interfacing.

See also

Other resources

Personal tools
  • Log in
  • Login with OpenID
About OLPC
About the laptop
About the tablet
OLPC wiki