How to capture a still image while previewing live video?

[Wesley J. Miller]

Hi,

  We need to simultaneously capture/preview video on a TI DM365 while asynchronously taking JPEG stills from the same video stream.  Playing around with gst-launch, it only seems to work correctly when v4l2src num-buffers=1. Sample working pipeline:

gst-launch -v v4l2src  num-buffers=1 always-copy=FALSE  input-src=composite \
! TIVidResize contiguousInputFrame=TRUE \
! 'video/x-raw-yuv,width=(int)736,height=(int)480' \
! queue \
! TIImgenc1  iColorSpace=UYVY oColorSpace=YUV420P qValue=75 engineName=codecServer \
! queue \
! filesink location=output.jpg



Have you considered multifilesink?  Makes a single output file for each frame that arrives in the sink. The downside of this is, of course, it makes a file for EVERY frame.  Also, because you are not keeping the entire stream you may loose (some?) timestamps and tags.  I don't know for sure.  If that information is really important to you, consider turning your stream in mjpeg and saving it into a container, Matroska is a good choice.  You will still have your individual frames that you can later extract and only one frame.

Wes



If I modify the above to remove num-buffers=1, or even just set num-buffers=2, it hangs and never produces a valid JPEG. I would have expected it to just overwrite output.jpg



If, I change this to something that is, for instance, previewing the video at thesame time, things break as well. Sample Pipeline:

gst-launch -v v4l2src always-copy=FALSE  input-src=composite \
! queue \
! tee name= t \
! 'video/x-raw-yuv,width=(int)736,height=(int)480' \
! tidisplaysink2 video-standard=vga display-output=lcd mmap-buffer=FALSE dma-copy=TRUE \
t. \
! queue \
! 'video/x-raw-yuv,width=(int)736,height=(int)480' \
! videorate \
! TIImgenc1  iColorSpace=UYVY oColorSpace=YUV420P qValue=75 engineName=codecServer \
! filesink location=output.jpg



Is it possible to create a gstreamer pipeline using “standard” parts to accomplish what I need, or will I need to modify my JPEG encoder element tomake this work?



Thanks!

Paul


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