173 lines
5.6 KiB
ReStructuredText
173 lines
5.6 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _dvb_introdution:
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************
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Introduction
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************
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.. _requisites:
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What you need to know
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=====================
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The reader of this document is required to have some knowledge in the
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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.
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Various DVB standards documents are available from http://www.dvb.org
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and/or http://www.etsi.org.
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It is also necessary to know how to access unix/linux devices and how to
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use ioctl calls. This also includes the knowledge of C or C++.
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.. _history:
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History
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=======
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The first API for DVB cards we used at Convergence in late 1999 was an
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extension of the Video4Linux API which was primarily developed for frame
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grabber cards. As such it was not really well suited to be used for DVB
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cards and their new features like recording MPEG streams and filtering
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several section and PES data streams at the same time.
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In early 2000, we were approached by Nokia with a proposal for a new
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standard Linux DVB API. As a commitment to the development of terminals
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based on open standards, Nokia and Convergence made it available to all
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Linux developers and published it on https://linuxtv.org in September
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2000. Convergence is the maintainer of the Linux DVB API. Together with
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the LinuxTV community (i.e. you, the reader of this document), the Linux
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DVB API will be constantly reviewed and improved. With the Linux driver
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for the Siemens/Hauppauge DVB PCI card Convergence provides a first
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implementation of the Linux DVB API.
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.. _overview:
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Overview
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========
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.. _stb_components:
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.. figure:: intro_files/dvbstb.*
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:alt: dvbstb.pdf / dvbstb.png
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:align: center
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Components of a DVB card/STB
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A DVB PCI card or DVB set-top-box (STB) usually consists of the
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following main hardware components:
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- Frontend consisting of tuner and DVB demodulator
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Here the raw signal reaches the DVB hardware from a satellite dish or
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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
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of a satellite frontend, this includes a facility for satellite
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equipment control (SEC), which allows control of LNB polarization,
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multi feed switches or dish rotors.
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- Conditional Access (CA) hardware like CI adapters and smartcard slots
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The complete TS is passed through the CA hardware. Programs to which
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the user has access (controlled by the smart card) are decoded in
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real time and re-inserted into the TS.
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- Demultiplexer which filters the incoming DVB stream
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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
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streams it also contains data streams with information about the
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programs offered in this or other streams of the same provider.
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- MPEG2 audio and video decoder
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The main targets of the demultiplexer are the MPEG2 audio and video
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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.
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:ref:`stb_components` shows a crude schematic of the control and data
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flow between those components.
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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 provides
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conditional access hardware.
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.. _dvb_devices:
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Linux DVB Devices
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=================
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The Linux DVB API lets you control these hardware components through
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currently six Unix-style character devices for video, audio, frontend,
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demux, CA and IP-over-DVB networking. The video and audio devices
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control the MPEG2 decoder hardware, the frontend device the tuner and
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the DVB demodulator. The demux device gives you control over the PES and
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section filters of the hardware. If the hardware does not support
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filtering these filters can be implemented in software. Finally, the CA
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device controls all the conditional access capabilities of the hardware.
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It can depend on the individual security requirements of the platform,
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if and how many of the CA functions are made available to the
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application through this device.
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All devices can be found in the ``/dev`` tree under ``/dev/dvb``. The
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individual devices are called:
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- ``/dev/dvb/adapterN/audioM``,
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- ``/dev/dvb/adapterN/videoM``,
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- ``/dev/dvb/adapterN/frontendM``,
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- ``/dev/dvb/adapterN/netM``,
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- ``/dev/dvb/adapterN/demuxM``,
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- ``/dev/dvb/adapterN/dvrM``,
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- ``/dev/dvb/adapterN/caM``,
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where N enumerates the DVB PCI cards in a system starting from 0, and M
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enumerates the devices of each type within each adapter, starting
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from 0, too. We will omit the “ ``/dev/dvb/adapterN/``\ ” in the further
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discussion of these devices.
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More details about the data structures and function calls of all the
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devices are described in the following chapters.
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.. _include_files:
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API include files
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=================
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For each of the DVB devices a corresponding include file exists. The DVB
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API include files should be included in application sources with a
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partial path like:
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.. code-block:: c
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#include <linux/dvb/ca.h>
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#include <linux/dvb/dmx.h>
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#include <linux/dvb/frontend.h>
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#include <linux/dvb/net.h>
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To enable applications to support different API version, an additional
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include file ``linux/dvb/version.h`` exists, which defines the constant
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``DVB_API_VERSION``. This document describes ``DVB_API_VERSION 5.10``.
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