write a python source plugin?

[Mathias]

Dear group,

is it possible to use the python bindings to create a source plugin?
I imagine something closely related to the imagefreeze plugin:
   - behave like imagefreeze most of the time (serve static image at
specified fps)
   - change image whenever new image arrives from somewhere else within
my (python) code.

Thanks!
   Mathias
_______________________________________________
gstreamer-devel mailing list
[hidden email]
http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[Oleksandr Lavrushchenko]

Hi,

is it possible to use the python bindings to create a source plugin?

just yesterday i faced with same question.
And i don't know how, but at first i lost from view most obvious place of getting information, this is:

- http://cgit.freedesktop.org/gstreamer/gst-python/tree/examples/filesrc.py

But fortunately i found next few very helpful links:

- http://guillaume.segu.in/blog/code/223/useful-paralellism-with-python/
- http://nullege.com/codes/search/gst.PushSrc
- http://svn.annodex.net/keystroke/trunk/textsrc.py

So basically you have to inherit from BaseSrc or PushSrc and implement do_create method. If your source support seeking than few other also.

On debian testing/unstable PushSrc seems not available in python-gst package so i inherited BaseSrc.

I imagine something closely related to the imagefreeze plugin:
  - behave like imagefreeze most of the time (serve static image at
specified fps)

Can't say something here, you may be need to give close attention to clocks in gstreamer to source at specific fps. Will be glad to hear how you do this if you will figure this out,  

  - change image whenever new image arrives from somewhere else within
my (python) code.

You just need to update you source buffer passed through do_create function.

Here is my code to push text string through udp (this like a little bit simplified version of filesrc example).

#!/usr/bin/env python
""" Source buf """
# -*- Mode: Python -*-
# vi:si:et:sw=4:sts=4:ts=4
#

import gobject
gobject.threads_init()

import pygst
pygst.require('0.10')
import gst

class Bufsrc(gst.BaseSrc):
    """ Push text """
    #here we register our plugin details
    __gstdetails__ = (
        "bufsrc test plugin",
        "bufsrc.py",
        "Source element that create a buffer",
        "Oleksandr Lavrushchenko <[e-mail]>")
 
    _src_template = gst.PadTemplate ("src",
                                     gst.PAD_SRC,
                                     gst.PAD_ALWAYS,
                                     gst.caps_new_any ())
 
    __gsttemplates__ = (_src_template,)
 
    def __init__ (self, *args, **kwargs):
        gst.BaseSrc.__init__(self)
        gst.info('creating srcpad')
        self.src_pad = gst.Pad (self._src_template)
        self.src_pad.use_fixed_caps()

        #self.add_pad (self.src_pad)

    def do_create(self, offset, length):
        buf = gst.Buffer("data\n")
        buf.timestamp = 0
        buf.duration = pow(2, 63) -1
        return gst.FLOW_OK, buf

# Register element class
gobject.type_register(Bufsrc)
gst.element_register(Bufsrc, 'bufsrc', gst.RANK_MARGINAL)

sink = gst.element_factory_make("udpsink", "sink")
sink.set_property("port", 5000)
sink.set_property("host", "127.0.0.1")

pusher = Bufsrc()

player = gst.Pipeline("player")
player.add(pusher, sink)
gst.element_link_many(pusher2, sink)

player.set_state(gst.STATE_PLAYING)

gobject.MainLoop().run()



_______________________________________________
gstreamer-devel mailing list
[hidden email]
http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[Sandino Flores Moreno]

Just out of curiosity:
Why python and not C or Vala?


On Thu, Jul 7, 2011 at 3:46 PM, Oleksandr Lavrushchenko
<[hidden email]> wrote:

> Hi,
>
>> is it possible to use the python bindings to create a source plugin?
>
> just yesterday i faced with same question.
> And i don't know how, but at first i lost from view most obvious place of
> getting information, this is:
>
> - http://cgit.freedesktop.org/gstreamer/gst-python/tree/examples/filesrc.py
>
> But fortunately i found next few very helpful links:
>
> - http://guillaume.segu.in/blog/code/223/useful-paralellism-with-python/
> - http://nullege.com/codes/search/gst.PushSrc
> - http://svn.annodex.net/keystroke/trunk/textsrc.py
>
> So basically you have to inherit from BaseSrc or PushSrc and implement
> do_create method. If your source support seeking than few other also.
>
> On debian testing/unstable PushSrc seems not available in python-gst package
> so i inherited BaseSrc.
>
>> I imagine something closely related to the imagefreeze plugin:
>>   - behave like imagefreeze most of the time (serve static image at
>> specified fps)
>
> Can't say something here, you may be need to give close attention to clocks
> in gstreamer to source at specific fps. Will be glad to hear how you do this
> if you will figure this out,
>
>>   - change image whenever new image arrives from somewhere else within
>> my (python) code.
>
> You just need to update you source buffer passed through do_create function.
>
> Here is my code to push text string through udp (this like a little bit
> simplified version of filesrc example).
>
> #!/usr/bin/env python
> """ Source buf """
> # -*- Mode: Python -*-
> # vi:si:et:sw=4:sts=4:ts=4
> #
>
> import gobject
> gobject.threads_init()
>
> import pygst
> pygst.require('0.10')
> import gst
>
> class Bufsrc(gst.BaseSrc):
>     """ Push text """
>     #here we register our plugin details
>     __gstdetails__ = (
>         "bufsrc test plugin",
>         "bufsrc.py",
>         "Source element that create a buffer",
>         "Oleksandr Lavrushchenko <[hidden email]>")
>
>     _src_template = gst.PadTemplate ("src",
>                                      gst.PAD_SRC,
>                                      gst.PAD_ALWAYS,
>                                      gst.caps_new_any ())
>
>     __gsttemplates__ = (_src_template,)
>
>     def __init__ (self, *args, **kwargs):
>         gst.BaseSrc.__init__(self)
>         gst.info('creating srcpad')
>         self.src_pad = gst.Pad (self._src_template)
>         self.src_pad.use_fixed_caps()
>
>         #self.add_pad (self.src_pad)
>
>     def do_create(self, offset, length):
>         buf = gst.Buffer("data\n")
>         buf.timestamp = 0
>         buf.duration = pow(2, 63) -1
>         return gst.FLOW_OK, buf
>
> # Register element class
> gobject.type_register(Bufsrc)
> gst.element_register(Bufsrc, 'bufsrc', gst.RANK_MARGINAL)
>
> sink = gst.element_factory_make("udpsink", "sink")
> sink.set_property("port", 5000)
> sink.set_property("host", "127.0.0.1")
>
> pusher = Bufsrc()
>
> player = gst.Pipeline("player")
> player.add(pusher, sink)
> gst.element_link_many(pusher2, sink)
>
> player.set_state(gst.STATE_PLAYING)
>
> gobject.MainLoop().run()
>
>
>
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
>
>

_______________________________________________
gstreamer-devel mailing list
[hidden email]
http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[Oleksandr Lavrushchenko]

Hi

On Sat, Jul 9, 2011 at 12:49 AM, Sandino Flores Moreno <[hidden email]> wrote:
>
> Just out of curiosity:
> Why python and not C or Vala?

First, this usually a question of taste.

Second, i see next reasons for me:

* it's easier to write, i love gst but usually it's C code for me a bit messy;
* easier to debug;
* less worries about memory management: pointers, memory allocation
and freeing, etc.;
* usually i want to prototype something and that's why i want see
results as much as possible, in python code usually much shorter so
faster to write.

If, when code will be working, i see some performance issues, i will
think about rewriting it from scratch in C. But at this point of time
i, at minimum, will have clean understanding how it's must work,
looking on python source.

P.S. I'm not a programmer by education, so addressing  all issues at
one time (C issues, algorithm issues, etc) may become the way to fail.
_______________________________________________
gstreamer-devel mailing list
[hidden email]
http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[Mathias]

First, thanks for the constructive comments.
I'm still busy writing my data source in python but the easiest way I have come across is to extend the videotestsource. Problem was that I cannot directly subclass it (not wrapped in python?) so I instantiated
videotestsrc via gst.element_factory_make, got its type and extended this:

xxx = gst.element_factory_make("videotestsrc", "video-source")
xclass = type(xxx)

Then, I can change the part where the data is actually created:

class yyy(xclass):
   def do_create(self, offset, length):
        try: self._cnt; # i have no custom constructor, so I have to test if its here already
        except: self._cnt = 100; self.tic = time.time() # no, instantiate this here
        origOutStat, origOutBuf = xclass.do_create(self, offset, length)     #parent output (videotestsrc)
        dat = scipy.zeros(len(origOutBuf),'uint8')   # my dummy output for testing
        dat[:] = self._cnt   # set to oscillating color, so we see something changing
        buf = gst.Buffer(dat.ravel()) # overwrite buffer
        self._cnt+=1
        return gst.FLOW_OK, buf

and register it:

gobject.type_register(yyy)
gst.element_register(yyy, 'yyy', gst.RANK_MARGINAL)


This is rather ugly, but I think I can work my way on from here.

Concerning the "why python" question:
The comments in the posting above are all correct, additionally it depends of course on my infrastructure. The data source that generates my images happens to be in python, so it is the easiest way to stay within python.

Thanks again,
   Mathias

[agrifoni]

Hi Mathias,
can you please post the full example, so it will be easier to understand for newbies, thanks!