GST cookbook

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Revision as of 13:24, 1 February 2011 by GChriss (talk | contribs) (Capture video from a v4l2 device, encode to an Ogg Theora file, mux with an ALSA audio source with delayed audio for a/v sync, then stream to IceCast: warning on loss of A/V sync)
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In addition to being a powerful multimedia infrastructure for applications Gstreamer is also a useful tool for general manipulations of multimedia data. By invoking gst-launch from the command-line with a custom pipeline many useful processing steps are possible.

Gstreamer also usually has good support for Xiph-related formats.

Unfortunately, it can be rather difficult to figure out an appropriate pipeline without a starting point.

Here are some useful examples:

Encode a .wav to Vorbis:

  • gst-launch filesrc location="INPUT.wav"  ! wavparse ! audioconvert ! vorbisenc ! oggmux ! filesink location="OUTPUT.ogg"

Dump a Theora video to PNGs:

  • gst-launch filesrc location="INPUT.ogv" ! oggdemux ! theoradec ! ffmpegcolorspace ! pngenc snapshot=false ! multifilesink location="OUTPUT%04d.png"

Transmux a MKV (containing vorbis and theora) to Ogg:

  • gst-launch filesrc location="INPUT.mkv" ! matroskademux name=d ! video/x-theora ! queue ! theoraparse ! oggmux name=mux ! filesink location="OUTPUT.ogv" d. ! audio/x-vorbis ! queue ! vorbisparse ! queue ! mux.

Encode a y4m to lossless Dirac in Ogg:

  • gst-launch filesrc location="INPUT.y4m" ! decodebin ! schroenc force-profile=vc2_main rate-control=lossless ! oggmux ! filesink location="OUTPUT.ogv"

Pull from a windows media stream, transcode to Ogg/Thera+Vorbis and send to a icecast server:

(requires purchasing fluendo plugins for decoding the encumbered codecs)

  • gst-launch uridecodebin uri=mms://SOURCE.SERVER.COM/path name=d ! queue max-size-time=100000000 ! ffmpegcolorspace ! theoraenc bitrate=800 ! oggmux name=mux ! shout2send ip=YOURICECAST.SERVER.COM port=8000 password=YOURPASSWORD mount=/OUTPUTFILENAME.ogv d. ! queue max-size-time=100000000 ! audioconvert ! vorbisenc ! mux.

Capture video from a webcam, encode to an Ogg Theora file, decode and display on screen, write to a file whose name is the current date+time, and stream to an IceCast server

  • gst-launch-0.10 --eos-on-shutdown v4l2src ! 'video/x-raw-yuv, width=640, height=480' ! videorate ! 'video/x-raw-yuv, framerate=15/1' ! queue max-size-bytes=100000000 max-size-time=0 ! theoraenc bitrate=150 ! oggmux ! tee name=ogged ! queue max-size-bytes=100000000 max-size-time=0 ! oggdemux ! theoradec ! xvimagesink sync=false force-aspect-ratio=true ogged. ! queue max-size-bytes=100000000 max-size-time=0 ! filesink location=`date +%F_%T`.ogv ogged. ! queue max-size-bytes=100000000 max-size-time=0 ! shout2send ip=YOURICECAST.SERVER.COM port=8000 password=YOURPASSWORD mount=/OUTPUTFILENAME.ogv streamname=YOURSTREAMNAME description=YOURDESCRIPTION genre=YOURGENRE url=YOURSTREAMURL ogged.

Capture video from a v4l2 device, encode to an Ogg Theora file, mux with an ALSA audio source with delayed audio for a/v sync, then stream to IceCast

gst-launch-0.10 --eos-on-shutdown v4l2src ! videoscale ! video/x-raw-yuv,width=320,height=240 ! ffmpegcolorspace ! videorate ! video/x-raw-yuv,framerate=15/1 ! queue max-size-bytes=100000000 max-size-time=0 ! theoraenc bitrate=350 ! queue max-size-bytes=100000000 max-size-time=0 ! oggmux name=mux alsasrc device=hw:1,0 latency-time=100 ! audioconvert ! vorbisenc ! queue max-size-bytes=100000000 max-size-time=0 ! mux. mux. ! queue max-size-bytes=100000000 max-size-time=0 ! shout2send password=hackme mount=/mountpoint.ogv

Note that the above pipeline will slowly lose audio/video synchronization due to hardware-level limitations in audio vs. video capture of media samples. FireWire and SDI-based capture does not have these limitations.

Create a video with an alpha channel from a sequence of PNG files

  • gst-launch-0.10 multifilesrc location=images%05d.png caps="image/png,framerate=1/1,pixel-aspect-ratio=1/1" num-buffers=95 ! pngdec ! videorate ! alphacolor ! "video/x-raw-yuv,format=(fourcc)AYUV" ! matroskamux ! filesink location=images_raw.mkv