Re: I see GStreamer Plugin Writer’s Guide PDF file, I don't understand mechanism that how do the element pad ask for (requests) sometimes and request pad on peer pad?

[Ian Davidson]

The element which creates the sometimes pad will raise a 'pad_added' signal.

Before you start your pipeline, you need to configure that element using 
a g_signal_connect so that you can detect that the pad has been added.  
In your signal handler, you will check which type of pad has been added 
(is it audio or video for example), so that you can link it to the 
appropriate flow.

On 25/12/2015 09:45, zhang007z wrote:
> I understand that the creating process of sometimes and request pad throught
> given example in this document ,but I don't understand that how to
> communicate to make this pad produce new sometimes and request pad between
> this element pad and peer element pad ?
> I don't know that when is gst_my_filter_loopfunc function invoked by what my
> code ?
>   you can specifically illustrate this communication (include query event and
> which functions does this process invoke?)between downstream pad and
> upstream pad if you know this issue . you also could enumerate some example
> to be convenient to my understand,such as demuxer or mixer
>
> if you take time for answering my stupid issue, think you in advance very
> much.