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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 16. Types and Properties</title><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="index.html" title="GStreamer Plugin Writer's Guide (1.10.4)"><link rel="up" href="part-advanced.html" title="Part III. Advanced Filter Concepts"><link rel="prev" href="section-allocation-query.html" title="GST_QUERY_ALLOCATION"><link rel="next" href="section-types-typefind.html" title="Typefind Functions and Autoplugging"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 16. Types and Properties</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="section-allocation-query.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Filter Concepts</th><td width="20%" align="right"> <a accesskey="n" href="section-types-typefind.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="chapter-building-types"></a>Chapter 16. Types and Properties</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="sect1"><a href="chapter-building-types.html#section-types-test">Building a Simple Format for Testing</a></span></dt><dt><span class="sect1"><a href="section-types-typefind.html">Typefind Functions and Autoplugging</a></span></dt><dt><span class="sect1"><a href="section-types-definitions.html">List of Defined Types</a></span></dt></dl></div><p>
There is a very large set of possible types that may be used to pass data
between elements. Indeed, each new element that is defined may use a new
data format (though unless at least one other element recognises that
format, it will be most likely be useless since nothing will be able to
link with it).
</p><p>
In order for types to be useful, and for systems like autopluggers to
work, it is necessary that all elements agree on the type definitions,
and which properties are required for each type. The <span class="application">GStreamer</span> framework
itself simply provides the ability to define types and parameters, but
does not fix the meaning of types and parameters, and does not enforce
standards on the creation of new types. This is a matter for a policy to
decide, not technical systems to enforce.
</p><p>
For now, the policy is simple:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
Do not create a new type if you could use one which already exists.
</p></li><li class="listitem"><p>
If creating a new type, discuss it first with the other <span class="application">GStreamer</span>
developers, on at least one of: IRC, mailing lists.
</p></li><li class="listitem"><p>
Try to ensure that the name for a new format is as unlikely to
conflict with anything else created already, and is not a more
generalised name than it should be. For example: "audio/compressed"
would be too generalised a name to represent audio data compressed
with an mp3 codec. Instead "audio/mp3" might be an appropriate name,
or "audio/compressed" could exist and have a property indicating the
type of compression used.
</p></li><li class="listitem"><p>
Ensure that, when you do create a new type, you specify it clearly,
and get it added to the list of known types so that other developers
can use the type correctly when writing their elements.
</p></li></ul></div><p>
</p><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="section-types-test"></a>Building a Simple Format for Testing</h2></div></div></div><p>
If you need a new format that has not yet been defined in our <a class="xref" href="section-types-definitions.html" title="List of Defined Types">List of Defined Types</a>, you will want to have some general
guidelines on media type naming, properties and such. A media type would
ideally be equivalent to the Mime-type defined by IANA; else, it should
be in the form type/x-name, where type is the sort of data this media type
handles (audio, video, ...) and name should be something specific for
this specific type. Audio and video media types should try to support the
general audio/video properties (see the list), and can use their own
properties, too. To get an idea of what properties we think are useful,
see (again) the list.
</p><p>
Take your time to find the right set of properties for your type. There
is no reason to hurry. Also, experimenting with this is generally a good
idea. Experience learns that theoretically thought-out types are good,
but they still need practical use to assure that they serve their needs.
Make sure that your property names do not clash with similar properties
used in other types. If they match, make sure they mean the same thing;
properties with different types but the same names are
<span class="emphasis"><em>not</em></span> allowed.
</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="section-allocation-query.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="part-advanced.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="section-types-typefind.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">GST_QUERY_ALLOCATION </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Typefind Functions and Autoplugging</td></tr></table></div></body></html>
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