Need to REMOVE an interface from a superclass.

[Stirling Westrup]

I am currently making a new element which is mostly controlling a set
of other contained elements, so we're subclassing Gst.Bin. As well, we
happen to be writing this in Python, but I think that's basically
irrelevant for my question.

GstBin has an annoying habit of treating any foo=bar parameter fed to
it as a proxy to be sent to a child named foo. As a result we just
spent several hours debugging our application, only to discover that a
misspelled element property was being silently ignored.

We would dearly love to NOT have the GstChildProxy interface active on
our GstBin as we want no external access to the contents of the bin.
However, I know of no safe way of disabling an existing interface.

Failing that, some way to intercept the property setting calls to the
GstChildProxy interface would at least allow us to issue an error in
case of a bad property.

We're actually seriously considering hacking up the source for GstBin
to produce an UnproxiedBin to derive from, but that sort of defeats
our attempts to move away from C to Python in the first place.




--
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http://www.linkedin.com/in/swestrup
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[Olivier Crête-3]

Hi,

This is a problem related to the  translation between the C and Python bindings. It's a separate interface in C. So you can either force Python to access g_object_set instead of gst_child_proxy_set .. 

Or maybe you can re-implement GstChildProxy in the subclass in a version that does nothing.

Olivier

On Fri, 2021-02-12 at 15:42 -0500, Stirling Westrup wrote:

I am currently making a new element which is mostly controlling a set

of other contained elements, so we're subclassing Gst.Bin. As well, we

happen to be writing this in Python, but I think that's basically

irrelevant for my question.

GstBin has an annoying habit of treating any foo=bar parameter fed to

it as a proxy to be sent to a child named foo. As a result we just

spent several hours debugging our application, only to discover that a

misspelled element property was being silently ignored.

We would dearly love to NOT have the GstChildProxy interface active on

our GstBin as we want no external access to the contents of the bin.

However, I know of no safe way of disabling an existing interface.

Failing that, some way to intercept the property setting calls to the

GstChildProxy interface would at least allow us to issue an error in

case of a bad property.

We're actually seriously considering hacking up the source for GstBin

to produce an UnproxiedBin to derive from, but that sort of defeats

our attempts to move away from C to Python in the first place.

-- 

Olivier Crête

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[Stirling Westrup]

On Fri, Feb 12, 2021 at 4:45 PM Olivier Crête
<[hidden email]> wrote:
>
> Hi,
>
> This is a problem related to the  translation between the C and Python bindings. It's a separate interface in C. So you can either force Python to access g_object_set instead of gst_child_proxy_set ..
>
> Or maybe you can re-implement GstChildProxy in the subclass in a version that does nothing.

Thanks, but I'm rather new to Python and haven't the slightest idea
how to do either of these things. There isn't a single Python example
I can find online where a GStreamer interface is defined, or even just
used, in a Python element.


--
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http://www.linkedin.com/in/swestrup
([phone]
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[Olivier Crête-3]

Hi,

I don't know of any GStreamer specific example, but it's the same as
GTK.. so here is a GtkTreeModel ...

https://gist.github.com/andialbrecht/4463278

You should also be able to call GObject.set_property(bin,...) to force
calling the right class

Olivier

On Tue, 2021-02-16 at 10:03 -0500, Stirling Westrup wrote:

> On Fri, Feb 12, 2021 at 4:45 PM Olivier Crête
> <[hidden email]> wrote:
> >
> > Hi,
> >
> > This is a problem related to the  translation between the C and Python bindings. It's a separate interface in C. So you can either force Python to access g_object_set instead of gst_child_proxy_set ..
> >
> > Or maybe you can re-implement GstChildProxy in the subclass in a version that does nothing.
>
> Thanks, but I'm rather new to Python and haven't the slightest idea
> how to do either of these things. There isn't a single Python example
> I can find online where a GStreamer interface is defined, or even just
> used, in a Python element.
>
>

--
Olivier Crête
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