Huh?: Gstreamer Basic Tutorial / API (3: Dynamic pipelines)

[Nicolas Dufresne]

Le mer. 15 mai 2019 23 h 25, R C <cjvijf at gmail.com> a écrit :

> so while messing with it,  I forgot to change teh second part, and even
> though it seems incosistent, can someone explain why this works?  (I am
> just putting the declarations here,  rewritting to ugly got's into
> something nicr is not the problem)
>
>
> in the main part the declarations I had are:
>
> // Create the elements
> data.source = gst_element_factory_make("uridecodebin", "source");
> data.audioconvert = gst_element_factory_make("audioconvert",
> "audioconvert");
> data.audiosink = gst_element_factory_make("autoaudiosink", "audiosink");
> data.videoconvert = gst_element_factory_make("videoconvert",
> "videoconvert");
> data.videosink = gst_element_factory_make("autovideosink", "videosink");
>
>
> and I forgot to make the changes in the second part (pad_added_handler),
> surprised it worked, and seems counter-intuitive?
>
> GstPad *audiosink_pad = gst_element_get_static_pad(data->audioconvert,
> "sink");
> GstPad *videosink_pad = gst_element_get_static_pad(data->videoconvert,
> "sink");
>
The names in the first part are the element names, while in this callback,
you are handling pad names. Pad names are chosen by the elements and follow
the pattern in the pad template (see gst-inspect-1.0 element to see the
template).



> but  ..  why??  How can it even find the right GstElement, since none of
> the are named "sink"?
>
>
> docs:
>
> ******************************************************************
> gst_element_get_static_pad ()
>
> GstPad <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstPad.html> *
> gst_element_get_static_pad (*GstElement <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstElement.html> *element*,
>                             *const gchar <https://gstreamer.freedesktop.org/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gchar> *name*);
>
> Retrieves a pad from *element* by name. This version only retrieves
> already-existing (i.e. 'static') pads.
>
> *Parameters*
>
> element a GstElement
> <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstElement.html>
> to find a static pad of.
>
> name the name of the static GstPad
> <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstPad.html>
> to retrieve.
> Returns
>
> the requested GstPad
> <https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstPad.html>
> if found, otherwise NULL
> <https://gstreamer.freedesktop.org/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS>.
> unref after usage.
>
> MT safe.
>
> ************************************************************************
>
>
>
> thanks,
>
>
> Ron
>
>
>
> On 5/15/19 8:33 PM, R C wrote:
>
> Hello,
>
> I am trying to get a little more familiar with gstreamer, and thought I'd
> do some
>
> of the "basic" programming tutorial examples.
>
>
> I did play with the 3rd example:
>
>
> https://gstreamer.freedesktop.org/documentation/tutorials/basic/dynamic-pipelines.html?gi-language=c
>
>
> If I copy the example, and compile it, it works, no surprise there. But
> when I change it and do the "exercise", I get some weirdness.
>
>
> What I noticed is (well I probably missed something)...  but the function
> call:
>
> data.sink = gst_element_factory_make ("autoaudiosink", "sink");
> According to the docs, the 2nd parameter can be 'whatever' you want to name it.
> Since I wanted to do the video part too, I figure I should change the name to
> "audio-something", and changed the second function call to:
>   data.convert = gst_element_factory_make ("audioconvert", "convert");   (original)
>   data.sink = gst_element_factory_make ("autoaudiosink", "audiosink");   (changed name)
>
> of course in the even handler (pad_added_handler), the name needs to be changed in to:
> GstPad *sink_pad = gst_element_get_static_pad (data->convert, "audiosink");
>
> Browsing through the code, that should be it, BUT it seems "sink_pad" always is NULL
>  and the pipeline elements don't/can't be linked. (see errors below)
>
> since this is supposed to be a simple example,  what am I missing?
>
> thanks,
>
> Ron
>
>
> errors:
> # ./basic-tutorial-3
> Pipeline state changed from NULL to READY:
> Received new pad 'src_0' from 'source':
>
> (basic-tutorial-3:14679): GStreamer-CRITICAL **: 20:22:54.991: gst_pad_is_linked: assertion 'GST_IS_PAD (pad)' failed
> It has type 'video/x-raw' which is not raw audio. Ignoring.
>
> (basic-tutorial-3:14679): GStreamer-CRITICAL **: 20:22:54.992: gst_object_unref: assertion 'object != NULL' failed
> Received new pad 'src_1' from 'source':
>
> (basic-tutorial-3:14679): GStreamer-CRITICAL **: 20:22:54.992: gst_pad_is_linked: assertion 'GST_IS_PAD (pad)' failed
>
> (basic-tutorial-3:14679): GStreamer-CRITICAL **: 20:22:54.992: gst_pad_link_full: assertion 'GST_IS_PAD (sinkpad)' failed
> Type is 'audio/x-raw' but link failed.
>
> (basic-tutorial-3:14679): GStreamer-CRITICAL **: 20:22:54.992: gst_object_unref: assertion 'object != NULL' failed
> Error received from element source: Internal data stream error.
> Debugging information: gstbasesrc.c(2950): gst_base_src_loop (): /GstPipeline:test-pipeline/GstURIDecodeBin:source/GstSoupHTTPSrc:source:
> streaming stopped, reason not-linked (-1)
>
>
> _______________________________________________
> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/gstreamer-devel/attachments/20190516/91c1e80d/attachment.html>