About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / DocBook / media / dvb / intro.xml

Custom Search

Based on kernel version 4.7.2. Page generated on 2016-08-22 22:44 EST.

1	<title>Introduction</title>
3	<section id="requisites">
4	<title>What you need to know</title>
6	<para>The reader of this document is required to have some knowledge in
7	the area of digital video broadcasting (DVB) and should be familiar with
8	part I of the MPEG2 specification ISO/IEC 13818 (aka ITU-T H.222), i.e
9	you should know what a program/transport stream (PS/TS) is and what is
10	meant by a packetized elementary stream (PES) or an I-frame.</para>
12	<para>Various DVB standards documents are available from
13	<ulink url="http://www.dvb.org" /> and/or
14	<ulink url="http://www.etsi.org" />.</para>
16	<para>It is also necessary to know how to access unix/linux devices and
17	how to use ioctl calls. This also includes the knowledge of C or C++.
18	</para>
19	</section>
21	<section id="history">
22	<title>History</title>
24	<para>The first API for DVB cards we used at Convergence in late 1999
25	was an extension of the Video4Linux API which was primarily developed
26	for frame grabber cards. As such it was not really well suited to be
27	used for DVB cards and their new features like recording MPEG streams
28	and filtering several section and PES data streams at the same time.
29	</para>
31	<para>In early 2000, we were approached by Nokia with a proposal for a
32	new standard Linux DVB API. As a commitment to the development of
33	terminals based on open standards, Nokia and Convergence made it
34	available to all Linux developers and published it on
35	<ulink url="https://linuxtv.org" /> in September 2000.
36	Convergence is the maintainer of the Linux DVB API. Together with the
37	LinuxTV community (i.e. you, the reader of this document), the Linux DVB
38	API will be constantly reviewed and improved. With the Linux driver for
39	the Siemens/Hauppauge DVB PCI card Convergence provides a first
40	implementation of the Linux DVB API.</para>
41	</section>
43	<section id="overview">
44	<title>Overview</title>
46	<figure id="stb_components">
47	<title>Components of a DVB card/STB</title>
48	<mediaobject>
49	<imageobject>
50	<imagedata fileref="dvbstb.pdf" format="PS" />
51	</imageobject>
52	<imageobject>
53	<imagedata fileref="dvbstb.png" format="PNG" />
54	</imageobject>
55	</mediaobject>
56	</figure>
58	<para>A DVB PCI card or DVB set-top-box (STB) usually consists of the
59	following main hardware components: </para>
61	<itemizedlist>
62	 <listitem>
64	<para>Frontend consisting of tuner and DVB demodulator</para>
66	<para>Here the raw signal reaches the DVB hardware from a satellite dish
67	or antenna or directly from cable. The frontend down-converts and
68	demodulates this signal into an MPEG transport stream (TS). In case of a
69	satellite frontend, this includes a facility for satellite equipment
70	control (SEC), which allows control of LNB polarization, multi feed
71	switches or dish rotors.</para>
73	</listitem>
74	 <listitem>
76	<para>Conditional Access (CA) hardware like CI adapters and smartcard slots
77	</para>
79	<para>The complete TS is passed through the CA hardware. Programs to
80	which the user has access (controlled by the smart card) are decoded in
81	real time and re-inserted into the TS.</para>
83	</listitem>
84	 <listitem>
85	 <para>Demultiplexer which filters the incoming DVB stream</para>
87	<para>The demultiplexer splits the TS into its components like audio and
88	video streams. Besides usually several of such audio and video streams
89	it also contains data streams with information about the programs
90	offered in this or other streams of the same provider.</para>
92	</listitem>
93	<listitem>
95	<para>MPEG2 audio and video decoder</para>
97	<para>The main targets of the demultiplexer are the MPEG2 audio and
98	video decoders. After decoding they pass on the uncompressed audio and
99	video to the computer screen or (through a PAL/NTSC encoder) to a TV
100	set.</para>
103	</listitem>
104	</itemizedlist>
106	<para><xref linkend="stb_components" /> shows a crude schematic of the control and data flow
107	between those components.</para>
109	<para>On a DVB PCI card not all of these have to be present since some
110	functionality can be provided by the main CPU of the PC (e.g. MPEG
111	picture and sound decoding) or is not needed (e.g. for data-only uses
112	like &#8220;internet over satellite&#8221;). Also not every card or STB
113	provides conditional access hardware.</para>
115	</section>
117	<section id="dvb_devices">
118	<title>Linux DVB Devices</title>
120	<para>The Linux DVB API lets you control these hardware components
121	through currently six Unix-style character devices for video, audio,
122	frontend, demux, CA and IP-over-DVB networking. The video and audio
123	devices control the MPEG2 decoder hardware, the frontend device the
124	tuner and the DVB demodulator. The demux device gives you control over
125	the PES and section filters of the hardware. If the hardware does not
126	support filtering these filters can be implemented in software. Finally,
127	the CA device controls all the conditional access capabilities of the
128	hardware. It can depend on the individual security requirements of the
129	platform, if and how many of the CA functions are made available to the
130	application through this device.</para>
132	<para>All devices can be found in the <constant>/dev</constant>
133	tree under <constant>/dev/dvb</constant>. The individual devices
134	are called:</para>
136	<itemizedlist>
137	<listitem>
139	<para><constant>/dev/dvb/adapterN/audioM</constant>,</para>
140	</listitem>
141	<listitem>
142	<para><constant>/dev/dvb/adapterN/videoM</constant>,</para>
143	</listitem>
144	<listitem>
145	<para><constant>/dev/dvb/adapterN/frontendM</constant>,</para>
146	</listitem>
147	 <listitem>
149	<para><constant>/dev/dvb/adapterN/netM</constant>,</para>
150	</listitem>
151	 <listitem>
153	<para><constant>/dev/dvb/adapterN/demuxM</constant>,</para>
154	</listitem>
155	 <listitem>
157	<para><constant>/dev/dvb/adapterN/dvrM</constant>,</para>
158	</listitem>
159	 <listitem>
161	<para><constant>/dev/dvb/adapterN/caM</constant>,</para></listitem></itemizedlist>
163	<para>where N enumerates the DVB PCI cards in a system starting
164	from&#x00A0;0, and M enumerates the devices of each type within each
165	adapter, starting from&#x00A0;0, too. We will omit the &#8220;
166	<constant>/dev/dvb/adapterN/</constant>&#8221; in the further discussion
167	of these devices.</para>
169	<para>More details about the data structures and function calls of all
170	the devices are described in the following chapters.</para>
172	</section>
174	<section id="include_files">
175	<title>API include files</title>
177	<para>For each of the DVB devices a corresponding include file exists.
178	The DVB API include files should be included in application sources with
179	a partial path like:</para>
181	<programlisting>
182		#include &#x003C;linux/dvb/audio.h&#x003E;
183	</programlisting>
184	<programlisting>
185		#include &#x003C;linux/dvb/ca.h&#x003E;
186	</programlisting>
187	<programlisting>
188		#include &#x003C;linux/dvb/dmx.h&#x003E;
189	</programlisting>
190	<programlisting>
191		#include &#x003C;linux/dvb/frontend.h&#x003E;
192	</programlisting>
193	<programlisting>
194		#include &#x003C;linux/dvb/net.h&#x003E;
195	</programlisting>
196	<programlisting>
197		#include &#x003C;linux/dvb/osd.h&#x003E;
198	</programlisting>
199	<programlisting>
200		#include &#x003C;linux/dvb/video.h&#x003E;
201	</programlisting>
203	<para>To enable applications to support different API version, an
204	additional include file
205	<constant>linux/dvb/version.h</constant> exists, which defines the
206	constant <constant>DVB_API_VERSION</constant>. This document
207	describes <constant>DVB_API_VERSION 5.10</constant>.
208	</para>
210	</section>
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.