How to make v4l2src reload buffer in PAUSED state

[Nicolas Dufresne]

Le jeudi 13 août 2020 à 14:53 -0500, dlw a écrit :
> I'm a bit of a gstreamer noob, so please bear with me...
> 
> I am trying to capture single images in a pipeline with that looks like the
> following:
> 
> v4l2src num-buffers=1 ! jpegenc quality=100 ! multifilesink
> location="/tmp/IMG%06d.jpg"
> 
> In my code I create the pipeline elements, link them and then set the
> pipeline to GST_STATE_PAUSED.
> 
> When I receive a "capture_image" command I then set the GST_STATE_PLAYING.
> 
> This works fantastic and I get an EOS and image written.  I then set the
> pipeline to GST_STATE_PAUSED waiting for the next "capture_image" command.
> 
> /The problem is that now the v4l2src buffer is empty and nothing will get
> written to the multifilesink on subsequent "capture_image" commands./
> 
> *Is there a way to make v4l2src send another image to its buffer and send it
> down to multifilesink?*  I can only get this to work if I set the pipeline
> to GST_STATE_READY, but timing is critical - it takes 600ms to capture the
> images from GST_STATE_READY, but only 300ms to capture from GST_STATE_PAUSED
> (multiple cameras and other processing happening that I've excluded for
> simplicity).

To follow your design, you'd simply need to send two events into the
pipeline, flush-start followed by flush-stop event. You'll have to bump
multifilesink index each time othewise the index is also reset by the
flush (and file will 

Now, why this is not idea is because while streaming, cameras run
algorithm to improve image quality. Meaning that the very first image
is not always in the best possible shape of what you camera can do.

What applications open do, is build a pipeline with a "view finder" / a
live preview of the image. And then can capture images on demand using
"last-sample" property and gst_video_convert_sample() API. Or, for more
advance usage, mais use a tee and other sinks, notably appsink.

Nicolas