Elements basics.py

From PiTiViWiKi

#!/usr/bin/env python

"""
gst.Element basics, this is a modified script of Brandon Lewis
"""

# PiTiVi does this for you, but in any stand-alone gstreamer script you need
# to do this before anything else
import gobject
gobject.threads_init()

# import gst and gtk
import gst
import gtk


class NewElement(gst.Element):
    """ A basic, buffer forwarding gstreamer element """

    #here we register our plugin details
    __gstdetails__ = (
        "NewElement plugin",
        "newelement.py",
        "gst.Element, that passes a buffer from source to sink (a filter)",
        "Stephen Griffiths <scgmk5@gmail.com>")
    
    #source pad (template): we send buffers forward through here
    _srctemplate = gst.PadTemplate ('src',
        gst.PAD_SRC,
        gst.PAD_ALWAYS,
        gst.caps_new_any())

    #sink pad (template): we recieve buffers from our sink pad
    _sinktemplate = gst.PadTemplate ('sink',
        gst.PAD_SINK,
        gst.PAD_ALWAYS,
        gst.caps_new_any())
    
    #register our pad templates
    __gsttemplates__ = (_srctemplate, _sinktemplate)

    def __init__(self, *args, **kwargs):   
        #initialise parent class
        gst.Element.__init__(self, *args, **kwargs)
        
        #source pad, outgoing data
        self.srcpad = gst.Pad(self._srctemplate)
        
        #sink pad, incoming data
        self.sinkpad = gst.Pad(self._sinktemplate)
        self.sinkpad.set_setcaps_function(self._sink_setcaps)
        self.sinkpad.set_chain_function(self._sink_chain)
        
        #make pads available
        self.add_pad(self.srcpad)
        self.add_pad(self.sinkpad)
    
    def _sink_setcaps(self, pad, caps):
        #we negotiate our capabilities here, this function is called
        #as autovideosink accepts anything, we just say yes we can handle the
        #incoming data
        return True
    
    def _sink_chain(self, pad, buf):
        #this is where we do filtering
        #and then push a buffer to the next element, returning a value saying
        # it was either successful or not.
        return self.srcpad.push(buf)

#here we register our class with glib, the c-based object system used by
#gstreamer
gobject.type_register(NewElement)





## this code creates the following pipeline, equivalent to 
## gst-launch-0.10 videotestsrc ! videoscale ! ffmpegcolorspace !
### NewElement ! autovideosink

# first create individual gstreamer elements

source = gst.element_factory_make("videotestsrc")
print "making new element"
newElement = NewElement()
print "made new element"
vscale = gst.element_factory_make("videoscale")
cspace = gst.element_factory_make("ffmpegcolorspace")
vsink  = gst.element_factory_make("autovideosink")

# create the pipeline

p = gst.Pipeline()
p.add(source, vscale, cspace, newElement,
    vsink)
gst.element_link_many(source, vscale, cspace, newElement,
    vsink)
# set pipeline to playback state

p.set_state(gst.STATE_PLAYING)

# start the main loop, pitivi does this already.

gtk.main()