Reading frames one-by-one to python/numpy

[Hjalmar Turesson]

Perfect example. It does exactly what I wanted.

But... The seek returns false (the other part works perfectly)

    CLI='filesrc location=%s ! decodebin ! appsink name=sink' % filename
    pipeline=Gst.parse_launch(CLI)
    # get sink
    appsink=pipeline.get_by_name("sink")
    # set to PAUSED to make the first frame arrive in the sink
    pipeline.set_state(Gst.State.PAUSED)
*    pipeline.seek_simple(Gst.Format.BUFFERS, Gst.SeekFlags.FLUSH,
frame_number)*
    smp = appsink.emit('pull-preroll')
    buf = smp.get_buffer()

    data=buf.extract_dup(0, buf.get_size())[:307200] # Only 1/2 of expected
RGB size
    frame = np.fromstring(data,dtype='uint8').reshape((480,640,1))


Thanks a lot,

Hjalmar

On Mon, Dec 7, 2015 at 1:47 PM, Tim Müller <tim at centricular.com> wrote:

> On Mon, 2015-12-07 at 13:30 -0300, Hjalmar Turesson wrote:
>
> Hi Hjalmar,
>
> This (C) example shows how to retrieve frames from appsink, perhaps you
> find it useful:
>
> http://cgit.freedesktop.org/gstreamer/gst-plugins-base/tree/tests/examp
> les/snapshot/snapshot.c
>
> It uses the pull-preroll signal/API, that only works once, if you want
> to retrieve one frame, and then another one, then just use the pull-
> sample API N times.
>
> There are two ways to use appsink: one is to have it emit a signal
> (new-sample) whenever a buffer arrives, and then you pull it in the
> callback). The other is to simply set the pipeline to PLAYING and then
> do pull-sample, which will block and wait for a simple if none is
> available yet then.
>
> Note that from the "new-sample" signal callback you can also return
> GST_FLOW_EOS if you don't want to be called again.
>
> Cheers
>  -Tim
>
> > Hi,
> >
> > I would like read individual frames to python/numpy for analysis.
> > That is, I want call a function that reads and returns 1 frame. I
> > thought I could do this with appsink, but I have 2 problems. 1) I
> > cannot return a frame from the callback function 2) It doesn't just
> > read 1 frame.
> >
> > Simple example that does not do what I want:
> >
> >    import gi
> >    gi.require_version('Gst', '1.0')
> >    from gi.repository import GObject, Gst, Gtk
> >    GObject.threads_init()
> >    Gst.init(None)
> >    ##########
> >
> >     CLI='filesrc location=testVideo.mp4 ! decodebin ! appsink
> > name=sink'
> >     pipeline=Gst.parse_launch(CLI)
> >     appsink=pipeline.get_by_name("sink")
> >     appsink.set_property("max-buffers",1)
> >     appsink.set_property('emit-signals',True)
> >     appsink.set_property('sync',False)
> >
> >     def on_new_buffer(appsink):
> >         sample = appsink.emit('pull-sample')
> >         #get the buffer
> >         buf=sample.get_buffer()
> >         data=buf.extract_dup(0,buf.get_size())
> >         return False  # Here I would like to return the frame
> >
> >     appsink.connect('new-sample', on_new_buffer)
> >     pipeline.set_state(Gst.State.PLAYING)
> >     pipeline.set_state(Gst.State.NULL)
> >
> > Is it possible to do what I want to do using appsink?
> >
> > Another strategy I tried is to use fdsink and read the data from that
> > location:
> >
> >     import os
> >
> >     readfd, writefd = os.pipe()
> >     frame_size_bytes = 460800
> >
> >     CLI='filesrc location=testVideo.mp4 ! decodebin ! fdsink
> > name=sink'
> >     pipeline=Gst.parse_launch(CLI)
> >     fdsink=pipeline.get_by_name("sink")
> >     fdsink.set_property("fd", readfd)
> >
> >     pipeline.set_state(Gst.State.PLAYING)
> >     data = os.read(readfd, frame_size_bytes)
> >     pipeline.set_state(Gst.State.PAUSED)
> >
> > This does not work either. The code hang at the data = os.read...
> > line, maybe trying to play the entire file before moving on.
> >
> > How can I read only one frame?
> >
> > Thanks,
> > Hjalmar
> > _______________________________________________
> > gstreamer-devel mailing list
> > gstreamer-devel at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
> --
> Tim Müller, Centricular Ltd - http://www.centricular.com
>
>
> _______________________________________________
> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>
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