[gst-devel] Questions about GstBuffer in handoff fakesrc function

[René Stadler]

Am Montag, den 04.06.2007, 12:46 +0200 schrieb Riccardo Corona:
> Hi,
> I've a fakesrc handoff function like this in which I get mpeg4 packet
> from the net:
> 
> static void cb_handoff (GstElement *fakesrc,
>         GstBuffer  *buffer,
>         GstPad     *pad,
>         gpointer    user_data) 
> {
> ......
> }
> 
> 
> And here's my doubts:
> 
> 1)The buffer->caps is null, even if i set a capsfilter between my
> fakesrc and the next element in the pipeline, I think that it must be
> set but if I try something like this: 
> 
> ..........
> pad->caps= gst_caps_new_simple ("video/mpeg",
>         "width", G_TYPE_INT, 720,
>         "height", G_TYPE_INT, 288,
>         "framerate",GST_TYPE_FRACTION,1,1, 
>         "mpegversion",G_TYPE_INT,4,
>         "systemstream",G_TYPE_BOOLEAN,false);
> gst_buffer_set_caps(buffer,pad->caps);
> .........
> 
You shouldn't set pad->caps.
> 
> or like this:
> 
> 
> ......... 
> GstPad *myPad;
> myPad->caps= gst_caps_new_simple ("video/mpeg",
>         "width", G_TYPE_INT, 720,
>         "height", G_TYPE_INT, 288,
>         "framerate",GST_TYPE_FRACTION,1,1,
>         "mpegversion",G_TYPE_INT,4,
>         "systemstream",G_TYPE_BOOLEAN,false);
> gst_buffer_set_caps(buffer,myPad->caps);
> ............
> 
> My app crash at the gst_caps_new_simple execution.It's hard for me to
> say why it crash but my first problem is to understand if is necessary
> to set the cap (I think yes) and moreover what can be the utility of
> the pads into the handoff function. 

You seem to ignore an important compiler warning which tells you that
you are missing the sentinel.  Append NULL to the argument list.

> 2)In my handoff I've compressed data since I get mpeg4 packets so the
> buffer->offset would be the byte offset of the first byte in
> buffer->malloc, is it right?Is it necessary to set manually the offset
> and offset_end or is it done automatically?Offset have strange values
> since it starts from 1 but after a few cycle it increments to much
> greater values (1,2,3,4,8456,12345...) and offset_end isn't set. 
> I really can't understand these two vars.
> 
> Any help will be very appreciate.
> Thank's and best regards.
> 
> -- 
> Riccardo Corona 

Figuring out how you are supposed to interact with fakesrc is so hard
because you are not supposed to do it -- have a look at the new appsrc
element (found in gst-plugins-bad) or write your own GstBaseSrc or
GstPushSrc derived element.

-- 
Regards,
  René Stadler