184 lines
6.1 KiB
ReStructuredText
184 lines
6.1 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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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 (Digital TV) 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 Digital TV standards documents are available for download at:
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- European standards (DVB): http://www.dvb.org and/or http://www.etsi.org.
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- American standards (ATSC): https://www.atsc.org/standards/
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- Japanese standards (ISDB): http://www.dibeg.org/
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It is also necessary to know how to access 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 Digital TV 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 Digital
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TV 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, Convergence was approached by Nokia with a proposal for a new
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standard Linux Digital TV 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. With the Linux driver for the Siemens/Hauppauge DVB PCI card,
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Convergence provided a first implementation of the Linux Digital TV API.
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Convergence was the maintainer of the Linux Digital TV API in the early
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days.
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Now, the API is maintained by the LinuxTV community (i.e. you, the reader
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of this document). The Linux Digital TV API is constantly reviewed and
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improved together with the improvements at the subsystem's core at the
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Kernel.
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.. _overview:
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Overview
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========
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.. _stb_components:
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.. kernel-figure:: dvbstb.svg
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:alt: dvbstb.svg
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:align: center
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Components of a Digital TV card/STB
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A Digital TV card or 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 digital TV demodulator
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Here the raw signal reaches the digital TV 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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.. note::
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Not every digital TV hardware provides conditional access hardware.
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Demultiplexer which filters the incoming Digital TV MPEG-TS 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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Audio and video decoder
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The main targets of the demultiplexer are 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 to a TV set.
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.. note::
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Modern hardware usually doesn't have a separate decoder hardware, as
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such functionality can be provided by the main CPU, by the graphics
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adapter of the system or by a signal processing hardware embedded on
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a Systems on a Chip (SoC) integrated circuit.
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It may also not be needed for certain usages (e.g. for data-only
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uses like "internet over satellite").
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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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.. _dvb_devices:
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Linux Digital TV Devices
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========================
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The Linux Digital TV 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 Digital TV demodulator. The demux device gives you control over the PES
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and 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 Digital TV cards in a system starting from 0, and
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``M`` 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 Digital TV devices a corresponding include file exists. The
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Digital TV 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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