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GStreamer
Some simple GStreamer examples (assuming that the v4l2loopback-device is /dev/video1).
$ gst-launch-1.0 v4l2src device=/dev/video1 ! xvimagesink
gst-launch-1.0 videotestsrc ! v4l2sink device=/dev/video1
Different videotestsrc patterns with different resolutions:
gst-launch-1.0 -v videotestsrc pattern=snow ! "video/x-raw,width=640,height=480,framerate=15/1,format=YUY2" ! v4l2sink device=/dev/video1
gst-launch-1.0 -v videotestsrc pattern=ball ! "video/x-raw,width=800,height=600,framerate=30/1,format=YUY2" ! v4l2sink device=/dev/video1
gst-launch-1.0 -v videotestsrc pattern=smpte horizontal-speed=1 ! "video/x-raw,width=1280,height=720,framerate=30/1,format=YUY2" ! v4l2sink device=/dev/video1
gst-launch-1.0 -v ximagesrc startx=1 starty=1 endx=320 endy=240 ! videoconvert ! "video/x-raw,format=YUY2" ! v4l2sink device=/dev/video1
gst-launch-1.0 -v filesrc location=test.avi ! avidemux ! decodebin ! videoconvert ! "video/x-raw,format=YUY2" ! v4l2sink device=/dev/video1
This producer is not infinite: when the file ends, the producer will stop.
Create frames, by splitting the input AVI into multiple PNG-files.
mkdir test
gst-launch-1.0 -v filesrc location=test.avi ! avidemux ! decodebin ! videoconvert ! pngenc snapshot=false ! multifilesink location=test/%05d.png
Use frames as infinite producer:
gst-launch-1.0 -v multifilesrc location=test/%05d.png loop=1 caps="image/png,framerate=30/1" ! pngdec ! videoconvert ! "video/x-raw,format=YUY2" ! v4l2sink device=/dev/video1
When sending frames to v4l2sink, the framerate can differ from framerate of the original video file. It can be set freely (60, 30, 15, 10, 5 or any other). This allows one to produce different framerates with the same frame set.
Decoding PNG can consume much CPU time. To reduce the load on the processor use raw YUV frames (see next example).
Create frames, by splitting the video.
When consuming the frames, we must know their dimension.
For the sake of making this example work, the video file "test.avi" is therefore scaled to 640x480@30.
In real life, you probably want to use the original dimension, rather than scale.
mkdir test
gst-launch-1.0 -v filesrc location=test.avi ! avidemux ! decodebin ! videoconvert ! videoscale ! videorate ! "video/x-raw,width=640,height=480,framerate=30/1,format=YUY2" ! multifilesink location=test/%05d.yuv
Use frames as infinite producer:
gst-launch-1.0 -v multifilesrc location=test/%05d.yuv loop=1 caps="video/x-raw,width=640,height=480,framerate=30/1,format=YUY2" ! videoconvert ! v4l2sink device=/dev/video1
When producing frames to v4l2sink, the framerate can differ from framerate of the original video file. It can be set freely (60, 30, 15, 10, 5 or any other). This allows to produce different framerates with the same frame set.
Decoding YUV frames does not consume much CPU time. But YUV frames consume much disk space and memory.
This last example (raw YUV-frames) doesn't really work yet with Gstreamer-1.0 ...
If you get the famous Internal data flow error when using GStreamer as a producer, you might want to add a tee element (to work around a bug in the current v4l2loopback (as of writing 0.10.0):
gst-launch-1.0 -v videotestsrc ! tee ! v4l2sink device=/dev/video1
With even newer GStreamer (>=1.14), this is supposed to no longer work and you could try this instead:
gst-launch-1.0 -v videotestsrc ! identity drop-allocation=1 ! v4l2sink device=/dev/video1
See also issue #83