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Commit 192f8bc1 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
Browse files

media: dvb/intro: adjust the notices about optional hardware 



Both CA and decoders are optional. Also, the presence or
absence has nothing to do on being a PCI card or not.

Nowadays, most hardware leaves the decoders to either the
GPU or to some ISP inside the SoC, instead of implementing
it inside the Digital TV part of the device.

So, change the wording to reflect the hardware changes.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 9a9bf230

Documentation/media/uapi/dvb/intro.rst

+17 −12
Original line number Diff line number Diff line
@@ -71,8 +71,7 @@ Overview 
A Digital TV card or set-top-box (STB) usually consists of the

following main hardware components:



-  Frontend consisting of tuner and digital TV demodulator



Frontend consisting of tuner and digital TV demodulator

   Here the raw signal reaches the digital TV hardware from a satellite dish or

   antenna or directly from cable. The frontend down-converts and

   demodulates this signal into an MPEG transport stream (TS). In case
@@ -80,34 +79,40 @@ following main hardware components: 
   equipment control (SEC), which allows control of LNB polarization,

   multi feed switches or dish rotors.



-  Conditional Access (CA) hardware like CI adapters and smartcard slots



Conditional Access (CA) hardware like CI adapters and smartcard slots

   The complete TS is passed through the CA hardware. Programs to which

   the user has access (controlled by the smart card) are decoded in

   real time and re-inserted into the TS.



-  Demultiplexer which filters the incoming DVB stream

   .. note::



      Not every digital TV hardware provides conditional access hardware.



Demultiplexer which filters the incoming DVB stream

   The demultiplexer splits the TS into its components like audio and

   video streams. Besides usually several of such audio and video

   streams it also contains data streams with information about the

   programs offered in this or other streams of the same provider.



-  MPEG2 audio and video decoder



MPEG2 audio and video decoder

   The main targets of the demultiplexer are the MPEG2 audio and video

   decoders. After decoding they pass on the uncompressed audio and

   video to the computer screen or (through a PAL/NTSC encoder) to a TV

   set.



   .. note::



      Modern hardware usually doesn't have a separate decoder hardware, as

      such functionality can be provided by the main CPU, by the graphics

      adapter of the system or by a signal processing hardware embedded on

      a Systems on a Chip (SoC) integrated circuit.



      It may also not be needed for certain usages (e.g. for data-only

      uses like “internet over satellite”).



:ref:`stb_components` shows a crude schematic of the control and data

flow between those components.



On a DVB PCI card not all of these have to be present since some

functionality can be provided by the main CPU of the PC (e.g. MPEG

picture and sound decoding) or is not needed (e.g. for data-only uses

like “internet over satellite”). Also not every card or STB provides

conditional access hardware.





.. _dvb_devices: