<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Things to check when writing an element</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="Appendices"
HREF="part-appendix.html"><LINK
REL="PREVIOUS"
TITLE="Appendices"
HREF="part-appendix.html"><LINK
REL="NEXT"
TITLE="Debugging"
HREF="section-checklist-debug.html"></HEAD
><BODY
CLASS="chapter"
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="part-appendix.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="section-checklist-debug.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="chapter"
><H1
><A
NAME="chapter-checklist-element"
></A
>Chapter 23. Things to check when writing an element</H1
><P
> This chapter contains a fairly random selection of things to take care
of when writing an element. It's up to you how far you're going to stick
to those guidelines. However, keep in mind that when you're writing an
element and hope for it to be included in the mainstream <SPAN
CLASS="application"
>GStreamer</SPAN
>
distribution, it <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>has to</I
></SPAN
> meet those requirements.
As far as possible, we will try to explain why those requirements are
set.
</P
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="section-checklist-states"
>23.1. About states</A
></H1
><P
></P
><UL
><LI
><P
> Make sure the state of an element gets reset when going to
<CODE
CLASS="classname"
>NULL</CODE
>. Ideally, this should set all
object properties to their original state. This function
should also be called from _init.
</P
></LI
><LI
><P
> Make sure an element forgets <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>everything</I
></SPAN
>
about its contained stream when going from
<CODE
CLASS="classname"
>PAUSED</CODE
> to <CODE
CLASS="classname"
>READY</CODE
>. In
<CODE
CLASS="classname"
>READY</CODE
>, all stream states are reset. An
element that goes from <CODE
CLASS="classname"
>PAUSED</CODE
> to
<CODE
CLASS="classname"
>READY</CODE
> and back to
<CODE
CLASS="classname"
>PAUSED</CODE
> should start reading the
stream from he start again.
</P
></LI
><LI
><P
> People that use <B
CLASS="command"
>gst-launch</B
> for testing have
the tendency to not care about cleaning up. This is
<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>wrong</I
></SPAN
>. An element should be tested using
various applications, where testing not only means to <SPAN
CLASS="QUOTE"
>"make
sure it doesn't crash"</SPAN
>, but also to test for memory leaks
using tools such as <B
CLASS="command"
>valgrind</B
>. Elements have to
be reusable in a pipeline after having been reset.
</P
></LI
></UL
></DIV
></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="part-appendix.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-checklist-debug.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Appendices</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="part-appendix.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Debugging</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
