Gstreamer does not sink to named pipe

问题:

I'm getting different behavior when the sink of a gst-launch pipeline is a named pipe vs a normal file.

I have a gst-launch pipeline which displays video from a camera on an OMAP embedded (linux) board and delivers the video as avi via a tee.

gst-launch -v -e omx_camera device=0 do-timestamp=1 mode=0 name=cam cam.src ! "video/x-raw-yuv, format=(fourcc)NV12, width=240, height=320, framerate=30/1" ! tee name=t1 t1. ! queue ! ducatih264enc profile=100 level=50 rate-preset=low-delay bitrate=24000 ! h264parse ! queue ! avimux ! filesink location=/tmp/camerapipe t1. ! queue ! dri2videosink sync=false

If I make

filesink location=/some/real/file t1.  

all is well

but I wish to read the output with a Java/opencv process, and when I do this I don't get anything to the java process. The gst-launch process does announc that it's changed to PLAY.

To simplify things instead of the java process I tail -f the named pipe

and also don't see any output, though in both cases the dri2videosink is displaying the video

With either tail or the java process, killing it also stops the gst-launch process, so obviously it's 'connected' in some sense.

Killing the gst-launch process with the tail running gets what looks like a few K, maybe 1 frame of data, after gst-launch exits.

I've tried saving to normal file and reading with the java process, that works, so I know it's not the data format.

回答1:

I am trying to do the same thing, I am using opencv in c and working in ubuntu though.

I did get the following to work:

I created a named pipe in /dev/ called video_stream using mkfifo make sur eyou have permissions to read/write to/from it or just use sudo.

Play with test video to a named pipe

sudo gst-launch -e videotestsrc ! video/x-raw-yuv, framerate=20/1, width=640, height=480 ! ffenc_mpeg4 ! filesink location=/dev/video_stream

Play from web cam to a named pipe:

sudo gst-launch -e v4l2src device=/dev/video0 !  ffenc_mpeg4 ! filesink location=/dev/video_stream

I then used the face detection tutorial at

http://docs.opencv.org/doc/tutorials/objdetect/cascade_classifier/cascade_classifier.html#cascade-classifier

to test everything, but changed my input from webcam 1 to the namedpipe.

  capture = cvCaptureFromCAM( -1 );

Becomes

 VideoCapture capture("/dev/video_stream");