1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Chapter 18. Media Controller</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API"><link rel="up" href="media_common.html" title="Part IV. Media Controller API"><link rel="prev" href="media_common.html" title="Part IV. Media Controller API"><link rel="next" href="media-controller-model.html" title="Media device model"></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 18. Media Controller</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="media_common.html">Prev</a> </td><th width="60%" align="center">Part IV. Media Controller API</th><td width="20%" align="right"> <a accesskey="n" href="media-controller-model.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="media_controller"></a>Chapter 18. Media Controller</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="media_controller.html#media-controller-intro">Introduction</a></span></dt><dt><span class="section"><a href="media-controller-model.html">Media device model</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="media-controller-intro"></a>Introduction</h2></div></div></div><p>Media devices increasingly handle multiple related functions. Many USB 2 cameras include microphones, video capture hardware can also output video, 3 or SoC camera interfaces also perform memory-to-memory operations similar to 4 video codecs.</p><p>Independent functions, even when implemented in the same hardware, can 5 be modelled as separate devices. A USB camera with a microphone will be 6 presented to userspace applications as V4L2 and ALSA capture devices. The 7 devices' relationships (when using a webcam, end-users shouldn't have to 8 manually select the associated USB microphone), while not made available 9 directly to applications by the drivers, can usually be retrieved from 10 sysfs.</p><p>With more and more advanced SoC devices being introduced, the current 11 approach will not scale. Device topologies are getting increasingly complex 12 and can't always be represented by a tree structure. Hardware blocks are 13 shared between different functions, creating dependencies between seemingly 14 unrelated devices.</p><p>Kernel abstraction APIs such as V4L2 and ALSA provide means for 15 applications to access hardware parameters. As newer hardware expose an 16 increasingly high number of those parameters, drivers need to guess what 17 applications really require based on limited information, thereby 18 implementing policies that belong to userspace.</p><p>The media controller API aims at solving those problems.</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="media_common.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="media_common.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="media-controller-model.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Part IV. Media Controller API </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Media device model</td></tr></table></div></body></html> 19