[gst-devel] gst-python problem: refcount for gst.Buffer too big?

Артём Попов artfwo at gmail.com
Sat Apr 22 03:35:01 CEST 2006


21.04.06, Edward Hervey<bilboed at gmail.com> написал(а):
> Hi,
> On 4/21/06, Артём Попов <artfwo at gmail.com> wrote:
> > Hi all,
> >
> > I'm trying to write a gst element in python, based on
> > GstBaseTransform. The core of such an element would be "transform" and
> > "transform_ip" methods, with receive GstBuffer arguments. Both of
> > these methods don't work for me, due to too large reference count of
> > Buffers passed to them. By the way, the "transform" method requires
> > "get_unit_size" virtual method to be implemented, the patch is here:
> >
> > http://bugzilla.gnome.org/show_bug.cgi?id=339248
> >
> > in "transform_ip", buffer refcount is 3, and that makes the buffer unwritable
> > in "transform", both buffer refcounts are 2, what makes output buffer
> > unwritable as well...
> >
> > def transform_ip (self, outbuf):
> >     print outbuf.__grefcount__ # always prints 3
> >     return gst.FLOW_OK
> >
> > def transform (self, inbuf, outbuf):
> >     print inbuf.__grefcount__ # always prints 2
> >     print outbuf.__grefcount__ # always prints 2
> >     return gst.FLOW_OK
> >
> > "gst_buffer_is_writable" checks, that the buffer refcount should be 1,
> > and gst-python uses just that to enable or disable data writing to the
> > buffer. So, how can I solve (or maybe workaround) this problem?
> > Thanks. --Artem
>   Would it be possible to see your code ? Seeing how you name your
> methods, I doubt it'll work properly.

Ah! Of course, they're "do_transform" and "do_transform_ip", and so
they are called in my code. It does nothing useful except set_caps,
get_unit_size and the transform test methods, that's why I didn't post
the complete class :)

>   Otherwise, we did refcount once too much, the bug and patch are
> available here (I can't commit right now since cvs is frozen) :
>   http://bugzilla.gnome.org/show_bug.cgi?id=339308
>   Please comment on the bug if it doesn't solve your issues.

Yeah, now the results are a bit different: here's what I get (full
code also posted in comment for bug #339308, also posted here for

def do_get_unit_size (self, caps):
    return 32 # buffer size (currently 2048) must be divisible by this number

def do_transform_ip (self, outbuf):
    print "ip:", outbuf.size, outbuf.__grefcount__ # will print "2048 2"
    return gst.FLOW_OK

def do_transform (self, inbuf, outbuf):
    print "noip:", inbuf.size, inbuf.__grefcount__ # will print "2048 1"
    print "noip:", outbuf.size, outbuf.__grefcount__ # will print "0 1"
    return gst.FLOW_OK

So... do_transform_ip is still unusable, because refcount is now
smaller but still more than 1. The do_transform method could actually
work now if outbuf was not zero-sized. Right now do_transform only
prints values _once_ and the program is freezed (I guess GStreamer is
waiting for it to fill the output buffer or something like that?)

Well, the patch fixed the bug at least partially, but it opens another
issue: outbuf in do_transform is zeroed. What do you think can be done
to solve this?


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