[gst-devel] Re: v4lsrc input channels

[Stefan Kost]

hi,

you need to bring the element to paused state first that get the ifaces. Reason 
behind is, that only then the elments know, wheter they can provide the iface of 
not. Then access it via GST_IMPLEMENTS_INTERFACE:
http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstImplementsInterface.html

Stefan

amo99 at libero.it wrote:
> Hi, i'm new to gstreamer.
> I wish to use interfaces (mixer, tuner, ecc.) to change devices properties.  I can't access them. Could you tell me which is the wrong step?
> 
> -----
> int main (int argc, char *argv[])
> {
>   gst_init (&argc, &argv);
>   const char * elementName = "alsamixer";
>   GstElement *source = gst_element_factory_make (elementName, "test");
>   if (source) {
>     GstMixer *mixer = GST_MIXER (source); /* it returns NULL and prints assertion msg*/
>     g_print("GstMixer instance: 0x%08X\n",source);
> 	
>     GstMixerClass *klassMixer = GST_MIXER_GET_CLASS(source); /* should be mixer but mixer is NULL*/
>     g_print("GstMixerClass: 0x%08X\n", klassMixer);
> 
>     if (klassMixer != NULL)	{
>       const GList *channels = klassMixer->list_tracks(mixer);
>       g_print("Channels 0x%08X\n",channels);
>     }
>     gst_object_unref (GST_OBJECT (source));
>   }
> ----
> Output on gststreamer v.0.9.6
> 
> (gstreamer:9666): GStreamer-CRITICAL **: gst_implements_interface_cast: assertion `gst_element_implements_interface (GST_ELEMENT (from), iface_type)' failed
> GstMixer instance: 0x08CED0C8
> GstMixerClass: 0x08D11FC0
> 
> ** (gstreamer:9666): CRITICAL **: gst_alsa_mixer_element_list_tracks: assertion `this != NULL' failed
> Channels 0x00000000
> 
> ----
> 
> Thanks in advance
> 
>  On Fri, 2005-11-04 at 18:21 +0100, flowolf wrote:
>  > How can I do the same thing with gstreamer?
>  
>  Using the GstTuner interface (gst/tuner/tuner.h).
>  
>  Cheers,
>  Ronald
> 
> 
> 
> 
> 
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