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GStreamer:GstLaunch

lastmod 2024-10-31created 2023-01-209 edits

Examples

Gstreamer is made up of a pipe and filer (also called pad) structure, and these are connected to each other with !.

Basic

The element that outputs video is called a Sink, and AutoVideoSink automatically selects the system's default Sink. Let's simply display a screen like a test pattern. 

$ gst-launch-1.0 videotestsrc ! autovideosink

Let's add a few Capabilities to this. 

$ gst-launch-1.0 videotestsrc ! video/x-raw, width=640, height=480 ! autovideosink

Connecting a webcam 

$ gst-launch-1.0 v4l2src device=/dev/video6 ! video/x-raw, width=640, height=480 ! autovideosink

Stream encoding

To send a stream over the network, it has to be compressed. Compression can be handled relatively simply by connecting a Pipe.

  • mjpeg: ! jpegenc
  • VP8: ! vp8enc
  • Mpeg2: ! avenc_mpeg4

can be connected like this.

Stream payload

Payloading is the work of packing raw or compressed data into a network protocol. GDP (Gstreamer Data Protocol) or RTP (Real Time Protocol) is usually used. The Payload pad is piped after the Encoder pad in the following form.

  • ! jpegenc ! rtpjpegpay
  • or ! vp8enc ! rtpv8pay
  • or ! avenc_mpeg4 ! rtpmp4vpay

Sending a stream 

$ gst-launch-1.0 -v v4l2src device=/dev/video6 ! video/x-raw, width=640, height=480 ! videoconvert ! jpegenc ! rtpjpegpay ! udpsink host=10.90.1.50 port=5000

Here the updsink host address is the IP address of the Receiver to send to.

Receiving a stream 

$ gst-launch-1.0 udpsrc port=5000 ! application/x-rtp,encoding-name=JPEG,payload=26 ! rtpjpegdepay ! jpegdec ! autovideosink

textoverlay

Output with pango-markup 

gst-launch-1.0 videotestsrc ! textoverlay name=text_sink text='<span foreground="blue" size="x-large">Blue text</span> is <i>cool</i>!'  ! videoconvert ! autovideosink

Branching a stream with Tee 

gst-launch-1.0 \
     videotestsrc ! video/x-raw,width=320,height=240 ! \
     timeoverlay halignment=center valignment=center font-desc="Sans, 32" ! \
     tee name=t \
     t. ! queue ! autovideosink \
     t. ! queue ! theoraenc bitrate=256 ! oggmux ! filesink location=test.ogg

Code used in answerjet-relay: 

gst-launch-1.0 videotestsrc is-live=true ! textoverlay text="1" ! videorate silent=true ! "video/x-raw,framerate=1/2" ! tee name=t t. ! answerjet_relay t. ! autovideosink

See also

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