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192 lines
6.7 KiB
XML
192 lines
6.7 KiB
XML
<title>Introduction</title>
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<section id="requisites">
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<title>What you need to know</title>
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<para>The reader of this document is required to have some knowledge in
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the area of digital video broadcasting (DVB) and should be familiar with
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part I of the MPEG2 specification ISO/IEC 13818 (aka ITU-T H.222), i.e
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you should know what a program/transport stream (PS/TS) is and what is
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meant by a packetized elementary stream (PES) or an I-frame.</para>
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<para>Various DVB standards documents are available from
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<ulink url="http://www.dvb.org" /> and/or
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<ulink url="http://www.etsi.org" />.</para>
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<para>It is also necessary to know how to access unix/linux devices and
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how to use ioctl calls. This also includes the knowledge of C or C++.
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</para>
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</section>
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<section id="history">
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<title>History</title>
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<para>The first API for DVB cards we used at Convergence in late 1999
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was an extension of the Video4Linux API which was primarily developed
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for frame grabber cards. As such it was not really well suited to be
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used for DVB cards and their new features like recording MPEG streams
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and filtering several section and PES data streams at the same time.
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</para>
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<para>In early 2000, we were approached by Nokia with a proposal for a
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new standard Linux DVB API. As a commitment to the development of
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terminals based on open standards, Nokia and Convergence made it
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available to all Linux developers and published it on
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<ulink url="http://www.linuxtv.org/" /> in September 2000.
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Convergence is the maintainer of the Linux DVB API. Together with the
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LinuxTV community (i.e. you, the reader of this document), the Linux DVB
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API will be constantly reviewed and improved. With the Linux driver for
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the Siemens/Hauppauge DVB PCI card Convergence provides a first
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implementation of the Linux DVB API.</para>
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</section>
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<section id="overview">
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<title>Overview</title>
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<figure id="stb_components">
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<title>Components of a DVB card/STB</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="dvbstb.pdf" format="PS" />
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</imageobject>
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<imageobject>
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<imagedata fileref="dvbstb.png" format="PNG" />
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</imageobject>
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</mediaobject>
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</figure>
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<para>A DVB PCI card or DVB set-top-box (STB) usually consists of the
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following main hardware components: </para>
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<itemizedlist>
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<listitem>
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<para>Frontend consisting of tuner and DVB demodulator</para>
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<para>Here the raw signal reaches the DVB hardware from a satellite dish
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or antenna or directly from cable. The frontend down-converts and
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demodulates this signal into an MPEG transport stream (TS). In case of a
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satellite frontend, this includes a facility for satellite equipment
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control (SEC), which allows control of LNB polarization, multi feed
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switches or dish rotors.</para>
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</listitem>
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<listitem>
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<para>Conditional Access (CA) hardware like CI adapters and smartcard slots
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</para>
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<para>The complete TS is passed through the CA hardware. Programs to
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which the user has access (controlled by the smart card) are decoded in
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real time and re-inserted into the TS.</para>
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</listitem>
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<listitem>
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<para>Demultiplexer which filters the incoming DVB stream</para>
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<para>The demultiplexer splits the TS into its components like audio and
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video streams. Besides usually several of such audio and video streams
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it also contains data streams with information about the programs
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offered in this or other streams of the same provider.</para>
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</listitem>
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<listitem>
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<para>MPEG2 audio and video decoder</para>
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<para>The main targets of the demultiplexer are the MPEG2 audio and
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video decoders. After decoding they pass on the uncompressed audio and
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video to the computer screen or (through a PAL/NTSC encoder) to a TV
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set.</para>
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</listitem>
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</itemizedlist>
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<para><xref linkend="stb_components" /> shows a crude schematic of the control and data flow
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between those components.</para>
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<para>On a DVB PCI card not all of these have to be present since some
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functionality can be provided by the main CPU of the PC (e.g. MPEG
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picture and sound decoding) or is not needed (e.g. for data-only uses
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like “internet over satellite”). Also not every card or STB
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provides conditional access hardware.</para>
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</section>
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<section id="dvb_devices">
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<title>Linux DVB Devices</title>
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<para>The Linux DVB API lets you control these hardware components
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through currently six Unix-style character devices for video, audio,
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frontend, demux, CA and IP-over-DVB networking. The video and audio
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devices control the MPEG2 decoder hardware, the frontend device the
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tuner and the DVB demodulator. The demux device gives you control over
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the PES and section filters of the hardware. If the hardware does not
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support filtering these filters can be implemented in software. Finally,
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the CA device controls all the conditional access capabilities of the
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hardware. It can depend on the individual security requirements of the
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platform, if and how many of the CA functions are made available to the
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application through this device.</para>
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<para>All devices can be found in the <emphasis role="tt">/dev</emphasis>
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tree under <emphasis role="tt">/dev/dvb</emphasis>. The individual devices
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are called:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/audioM</emphasis>,</para>
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</listitem>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/videoM</emphasis>,</para>
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</listitem>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/frontendM</emphasis>,</para>
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</listitem>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/netM</emphasis>,</para>
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</listitem>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/demuxM</emphasis>,</para>
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</listitem>
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<listitem>
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<para><emphasis role="tt">/dev/dvb/adapterN/caM</emphasis>,</para></listitem></itemizedlist>
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<para>where N enumerates the DVB PCI cards in a system starting
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from 0, and M enumerates the devices of each type within each
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adapter, starting from 0, too. We will omit the “<emphasis
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role="tt">/dev/dvb/adapterN/</emphasis>” in the further dicussion
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of these devices. The naming scheme for the devices is the same wheter
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devfs is used or not.</para>
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<para>More details about the data structures and function calls of all
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the devices are described in the following chapters.</para>
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</section>
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<section id="include_files">
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<title>API include files</title>
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<para>For each of the DVB devices a corresponding include file exists.
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The DVB API include files should be included in application sources with
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a partial path like:</para>
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<programlisting>
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#include <linux/dvb/frontend.h>
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</programlisting>
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<para>To enable applications to support different API version, an
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additional include file <emphasis
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role="tt">linux/dvb/version.h</emphasis> exists, which defines the
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constant <emphasis role="tt">DVB_API_VERSION</emphasis>. This document
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describes <emphasis role="tt">DVB_API_VERSION 3</emphasis>.
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</para>
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</section>
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