Add bindings for gst_element_class*() and similar class functions

[fengalin]

I'm following this tutorial in order to implement a tee in my audio pipeline.

To get the src pads from the tee, the tutorial proposes using:

  tee_src_pad_template = gst_element_class_get_pad_template (GST_ELEMENT_GET_CLASS (tee), "src_%d");
  tee_audio_pad = gst_element_request_pad (tee, tee_src_pad_template, NULL, NULL);

ElementClass is not generated, but I found get_compatible_pad_template on Element. So I tried this in the connect_pad_added callback (my source is a uridecodebin):

    [...]
    let tee = gst::ElementFactory::make("tee", None).unwrap();
    pipeline.add(&tee).unwrap();

    let tee_sink = tee.get_static_pad("sink").unwrap();
    assert_eq!(src_pad.link(&tee_sink), gst::PadLinkReturn::Ok);

    let pad_tmpl = PadTemplate::new("src_%d",
        PadDirection::Src,
        PadPresence::Request,
        &Caps::new_any()
    );
    let tee_src_pad_tmpl = tee.get_compatible_pad_template(&pad_tmpl).unwrap();
    let tee_src_pad = tee.request_pad(&tee_src_pad_tmpl, None, None)
        .expect("Couldn't get src pad from gst tee");

Which fails on tee.request_pad() with the following message:

(.:8073): GStreamer-CRITICAL **: gst_element_request_pad: assertion 'templ->presence == GST_PAD_REQUEST' failed

I can continue investigating, but if you tell me that this isn't going to work, I'd implement the binding to ElementClass instead.

[sdroege]

You can use tee.get_request_pad("src_%u") for example. But not having the gst_element_class_* functions is indeed problematic. Should add them

[sdroege]

Also for your code with get_compatible_pad_template to work, you need to create a sink pad template IIRC. It gets a pad template that can be linked to yours, so of the opposite direction.

[fengalin]

Thank you! Using tee.get_request_pad("src_%u") works indeed! I tried it before, but with "src_%d", like in the C example and it failed.

[sdroege]

Thanks, fixed in the docs (and simplified the tutorial): http://cgit.freedesktop.org/gstreamer/gst-docs/commit/?id=1a9f0541be419798eacc6fedf50cadadebca352b