<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Fixed caps</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79;charset=UTF-8"><LINK
REL="HOME"
TITLE="GStreamer Plugin Writer's Guide (0.10.36)"
HREF="index.html"><LINK
REL="UP"
TITLE="Caps negotiation"
HREF="chapter-negotiation.html"><LINK
REL="PREVIOUS"
TITLE="Caps negotiation"
HREF="chapter-negotiation.html"><LINK
REL="NEXT"
TITLE="Downstream caps negotiation"
HREF="section-nego-downstream.html"></HEAD
><BODY
CLASS="sect1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
><SPAN
CLASS="application"
>GStreamer</SPAN
> Plugin Writer's Guide (0.10.36)</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="chapter-negotiation.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 10. Caps negotiation</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="section-nego-downstream.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="section-nego-fixedcaps"
>10.2. Fixed caps</A
></H1
><P
> The simplest way in which to do caps negotiation is setting a fixed
caps on a pad. After a fixed caps has been set, the pad can not be
renegotiated from the outside. The only way to reconfigure the pad
is for the element owning the pad to set a new fixed caps on the pad.
Fixed caps is a setup property for pads, called when creating the pad:
</P
><PRE
CLASS="programlisting"
> [..]
pad = gst_pad_new_from_template (..);
gst_pad_use_fixed_caps (pad);
[..]
</PRE
><P
> The fixed caps can then be set on the pad by calling
<CODE
CLASS="function"
>gst_pad_set_caps ()</CODE
>.
</P
><PRE
CLASS="programlisting"
> [..]
caps = gst_caps_new_simple ("audio/x-raw-float",
"width", G_TYPE_INT, 32,
"endianness", G_TYPE_INT, G_BYTE_ORDER,
"buffer-frames", G_TYPE_INT, <bytes-per-frame>,
"rate", G_TYPE_INT, <samplerate>,
"channels", G_TYPE_INT, <num-channels>, NULL);
if (!gst_pad_set_caps (pad, caps)) {
GST_ELEMENT_ERROR (element, CORE, NEGOTIATION, (NULL),
("Some debug information here"));
return GST_FLOW_ERROR;
}
[..]
</PRE
><P
> Elements that could implement fixed caps (on their source pads) are,
in general, all elements that are not renegotiable. Examples include:
</P
><P
></P
><UL
><LI
><P
> A typefinder, since the type found is part of the actual data stream
and can thus not be re-negotiated.
</P
></LI
><LI
><P
> Pretty much all demuxers, since the contained elementary data
streams are defined in the file headers, and thus not
renegotiable.
</P
></LI
><LI
><P
> Some decoders, where the format is embedded in the data stream
and not part of the peercaps <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>and</I
></SPAN
> where the
decoder itself is not reconfigurable, too.
</P
></LI
></UL
><P
> All other elements that need to be configured for the format should
implement full caps negotiation, which will be explained in the next
few sections.
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="chapter-negotiation.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="section-nego-downstream.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Caps negotiation</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="chapter-negotiation.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Downstream caps negotiation</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
