GStreamer/Developers

From OLPC

Jump to: navigation, search

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


Contents

Getting started programming

Getting started with GStreamer with Python

Recipes

Camera

  • Have to script v4l2 via gstreamer to capture a single frame from the camera. See sugar/shell/intro/glive.py 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 may 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

Examples

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

Stdout:

... ! 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=192.168.1.100 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

Playback:

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

Notes

Colorspace

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

glive.py used wav rather than vorbis. Why?

Elements

Adapters:

Video characteristics:

Audio characteristics:

File I/O:

Video sources:

Audio sources:

Coding video:

Coding audio:

Wrapping:

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

Method1

xo sending video:

gst-launch v4l2src ! video/x-raw-yuv,width=320,height=240,framerate=\(fraction\)5/1 ! ffmpegcolorspace ! jpegenc ! multipartmux ! tcpserversink host=192.168.2.1 port=5000

xo recieving video:

gst-launch tcpclientsrc host=192.168.2.2 port=5001 ! multipartdemux ! jpegdec ! autovideosink

Method2

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=192.168.1.1 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=192.168.2.129 port=5000 alsasrc ! queue ! audio/x-raw-int,rate=8000,channels=1,depth=8 ! audioconvert ! speexenc ! queue ! tcpserversink host=192.168.2.129 port=5001

Receiving XO:

gst-launch-0.10 udpsrc port=5000 ! queue ! smokedec ! queue ! autovideosink tcpclientsrc host=192.168.2.129 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
Projects
OLPC wiki
Toolbox
In other languages