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=DVB in general=
=DVB in general=
chapter you information about DVBin general. No part of this chapter contains specifics for setting up your MythTV system as a DVB receiveris covered in the chapters.
Revision as of 09:38, 16 October 2008
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This page is up-to-date to MythTV version 0.20
DVB in general
--> You can skip this chapter if you're only interested in configuring and setting up MythTV
This chapter gives you background information about Digital Video Broadcast (DVB) in general. No part of this chapter contains specifics for setting up your MythTV system as a DVB receiver, this is covered in the following chapters.
What is DVB?
(Digital Video Broadcasting) is the most popular standard for digital TV. Other standards include ATSC, and Digicipher II (DCII). DVB is also the name of the Linux drivers used for most DTV receivers in Linux, including ATSC, DCII and other MPEG-2 and MPEG-4 based broadcast standards.
DVB was initially based on the MPEG-2 compression and packet formats, but has recently been extended to support MPEG-4 AVC/H.264 streams as well. The physical part comes in three variants:
- Terrestrial (over-the-air with an antenna) (DVB-T)
- Cable (DVB-C)
- Satellite (DVB-S)
Some channels (especially pay channels) are encrypted. There's a standardized decryption hardware slot called "Common Interface" (CI) for the decryption hardware called "Conditional Access Module" (CAM), which usually also needs a smartcard for authorization and accounting.
CI+ or Common Interface Plus
CI+ (Common Interface Plus) is a specification that extends the DVB Common Interface (DVB-CI). It was developed by consumer electronic firms Panasonic, Philips, Samsung and Sony, as well as pay-TV technology company SmarDTV and fabless chip maker NEOTION.
A first draft of the specification has been put up for review early in 2008. CI+ implements a form of copy protection between a Conditional Access Module (CAM) and the digital television receiver (DTV).
By making use of certificates and a certification authority, a trusted channel is formed between the CAM and DTV, when scrambled content is being received. In the original CI standard, decrypted content could be sent over the PCMCIA interface unscrambled.
DVB is widely used in Europe and Asia, over-the-air (DVB-T), via cable (DVB-C) and via satellite (DVB-S). There are hundreds of DVB-S channels available in Europe on the satellite fleets of Astra and Eutelsat, almost all of them "free to air" (unencrypted), including all the major free stations. DVB-C is also widely used in european cable tv networks, with different modulation schemes and also including HDTV. DVB-T is being deployed at the moment in UK, Germany, France, Australia, Spain, Netherlands, Denmark, Sweden and other countries as a replacement for the classic analog TV over antenna.
In the US, Dish Network uses standard DVB (with Nagravision 2 encryption), while DirecTV uses an earlier, incompatible system that predates DVB, sometimes called DBS (Digital Broadcast Satellite). In Canada, StarChoice uses DCII and Bell ExpressVu uses standard DVB. Most of what's available via FTA in North America is religious programming, or programming not intended for mass consumption. Still, many hobbyists enjoy receiving FTA broadcasts, and a PC with a DVB card is one of the best ways to receive these broadcasts.
Cable operators in the US were supposed to move to ATSC for by 2006 for broadcast channels but few have complied with the law. Most major TV stations in the US are now transmitting a digital signal in ATSC in addition to their analog signal. This can be received with a conventional TV antenna and an appropriate decoder, including several ATSC cards supported by MythTV.
DVB-S specifics (satellite)
In this paragraph you'll find specific information about using DVB-S
DiSEqC (Digital Satellite Equipment Control) pronounced "Die-Sec" is a special communication protocol for use between a satellite receiver and a device such as a multi-dish switch or a small dish antenna rotor. It is compatible with the actuators used to rotate large C band dishes if used with a DiSEqC positioner. It relies only on the coaxial cable to transmit both bidirectional data/signals and power.
DiSEqC is commonly used to control multiswitches and claims to be more flexible than 13/18 volt and 22 kHz tone or ToneBurst/MiniDiSEqC techniques. Despite its name, it has been used on fully analogue or only partially digital-capable (Astra Digital Radio) satellite receivers .
A number of variations of DiSEqC exist:
DiSEqC 1.0, which allows switching between up to 4 satellite sources
DiSEqC 1.1, which allows switching between up to 16 sources
DiSEqC 1.2, which allows switching between up to 16 sources, and control of a simple horizontal-panning satellite motor
DiSEqC 2.0, which adds bi-directional communications to DiSEqC 1.2
All four variations were standardised by February 1998, prior to general use of digital satellite television. They are all back compatible - a DiSEqC 2.0 receiver can control a 1.0 switch; but a 1.0 receiver cannot control motorised features. The terms DiSEqC 1.3 and 2.3 are often used by manufacturers and retailers to refer to other protocols (1.3 usually refers to USALS receivers), but these uses are not authorised by Eutelsat, the developers of the system, who now act as the protocol standards agency. Eutelsat apparently developed the system to allow satellite users in Continental Europe to switch between the more popular SES Astra 1 block of satellites and Eutelsat's own Hotbird system. As a result, the vast majority of European satellite receivers support at least DiSEqC 1.2, with the notable exception of all set top boxes manufactured under the Sky Digibox name. All supporting receivers have received certification to carry a logo specifying which variation of DiSEqC they support.
Hardware support depends on the driver availability for your operating system. For Linux, check the following pages on the linuxtv.org wiki:
- DVB-C (Cable) - http://www.linuxtv.org/wiki/index.php/DVB-C_Devices
- DVB-S (Satellite) - http://www.linuxtv.org/wiki/index.php/DVB-S_Devices
- DVB-T (Terrestrial) - http://www.linuxtv.org/wiki/index.php/DVB-T_Devices
Beginning with DVB
Many details of DVB usage differ from analogue usage, and this can cause confusion. In particular:
- Many instructions assume an analogue tuner card, and some of the details do not apply to DVB.
- Analogue cards with hardware MPEG2 encoders reduce the CPU load. DVB receives MPEG natively, so it doesn't need an encoder.
- Transcoding profiles were a little different and nonsensical for DVB, though this may have changed with 0.19 or 0.20.
- Recording profiles are not so useful, since the bit rate and frame size are defined by the received signal and can't be changed.
You can test whether DVB is working on your Linux machine (before installing MythTV) using the Dvb-apps software suite.
- Tuner cards that work
- LinuxTV DVB support - The DVB layer of Mythtv with list of supported hardware
- Dvb-apps - usefull tools when working with DVB
- Example DVB-S MythTV Setup - Useful information when using DVB-T and DVB-S.
- http://linuxtv.org/wiki - The linuxtv.org DVB Wiki (These guys created the dvb-apps tools)!
- http://www.acaciaclose.co.uk - MythTV 0.18/0.19 DVB on SUSE 9.3/10.0 setup guide
- http://www.ethics-gradient.net/myth/mythdvb.html - Martin Smiths DVB-T Setup Guide
- http://www.mythbox.co.uk - MythTV and PVR setup guide for DVB-T in the UK
- http://www.dvbstreamexplorer.com - An MPEG-2/DVB Transport Stream Analyzer for Windows
- Some utilities/sample code aimed at using radio recordings from DVB with iTunes / iPod / Podcasts