[linux-dvb] Re: ATSC/DTV question

[Daniel Schmelzer <dschmelzer@hotmail.com>]

Hi All--

Pardon me if some of this has already been addressed or it is old news.  I 
just picked up the mailing list and this thread.

There are at least three boards on the consumer market that pick up an ATSC 
stream:  Hauppauge's WinTV-D, Hauppauge's WinTV-HD, and Telemann's HiPix.  
So far, the Telemann board is the only one with accompanying Windows 
software to save an ATSC transport stream to disk.  It does so in one-minute 
files with a Telemann header attached.  Hauppauge also has a beta stream 
capture program for its WinTV-D that captures the stream raw.

Elecard's (www.elecard.com) MPEG decoder has a demuxer that can demux the 
raw ATSC stream that the WinTV-D capture program saves to disk.  The demuxer 
is in the form of a DirectShow filter and breaks out all of the program 
streams in the transport stream--most often, US TV stations include at least 
two video streams and two audio streams in one raw ATSC stream.

I suspect that the differences between the DVB and ATSC streams is *quite* 
small, because Elecard was able to modify its demuxer in one evening to 
handle the raw ATSC files.  However, as has been pointed out, I'm not sure 
about all of the multiple program streams, channel mapping and other stuff 
going on that are needed to fill out the functionality...

As for the hardware, both the HiPix and the WinTV-HD are based on the Janus 
reference design, so if you support one, you can support the other (and any 
subsequent cards) fairly easily.

Other substantial designs include Conexant's D-Stream design, which strips 
all of the hardware decoding in favor of software-only decoding.  I think 
that it uses a modified 878a chip and DMAs the ATSC stream to memory.  I 
haven't seen any consumer cards based on this yet, if only because few 
machines can handle the load on a 1080i stream.

IIRC, the bandwidth for ATSC is 6 MHz--channels can be found exactly where 
they were with UHF.  Subchannels are just different substreams within the 
raw ATSC stream.

Not surprisingly, the ATSC info can be found at www.atsc.org.

Please let me know if you need any testing done at dschmelzer@hotmail.com.  
I have the HiPix and access to digital channels that have various types of 
streams (480i, 480p, 720p, 1080i), but little coding knowledge or experience 
(and very modest experience with Linux).  I can also provide some raw ATSC 
files and HiPix headed files if you need them.

Regards--

Dan


-------
The DVB demux software works by filtering out IP packets from DSM-CC
sections, and DSM-CC sections from TS packets. (Checkout the standard  EN
101 192 (V1.2.1: 06/99) and the guidelines TR 101 202 (V1.1.1: 02/99) from
http://www.etsi.org/ or directly http://webapp.etsi.org/pda/QueryForm.asp)

First you must find out how ATSC encapsulates its IP data into the TS from
the ATSC standards (I would be interested to know when you find out). Then
modify demux.h for ATSC and demux.c for your hardware. (I suspect demux.h
changes will be small)

Next up is to find out what tuning parameters are needed for your ATSC
frontend, such as how are centre frequency, modulation parameters, bandwidth
etc. specified and which are always the same. e.g. DVB-T signals can be on
bandwidths of 6, 7 and 8 MHz, but maybe ATSC uses a fixed bandwidth. I would
also be delighted to find out what you discover for this. Then modify
frontend.h for ATSC and frontend.c for your hardware. /dev/ost/vsb8fe might
be a suitable location (but make sure you don't link into /dev/ost/qpskfe
instead)

Assuming you already know the correct tuning parameters and demux parameters
(PID, MAC etc.) - that's all you need for IP data.

However, if you need SI information (i.e. the service information tables)
then you will need to parse those to work out the demux parameters for a
particular stream. I think VDR has been doing this for DVB, and I'm pretty
sure ATSC uses DSM-CC sections to put SI in so maybe this would not be a big
task by reusing code.

Vague disclaimer: I've never done anything with ATSC (other than read a
little) so don't blame me if all goes wrong, but I hope this helps you.

Cheers,
Rod.

>-----Original Message-----
>From: ext Keith Craigie [mailto:kcraigie@mediabolic.com]
>Sent: 20 January, 2001 0:04
>To: Rod.Walsh@nokia.com
>Cc: rjkm@convergence.de; linux-dvb@linuxtv.org
>Subject: Re: [linux-dvb] Re: ATSC/DTV question
>
>
>Well probably the first course of action is to actually work
>on supporting
>an ATSC-compliant DTV receiver board for Linux.  As there
>don't seem to be
>any on the market - we're probably going to port Broadlogic's DTA-100
>driver ourselves.
>
>Our goal is to be able to receive the data IP packets from the
>transmission, muxed in with the standard DTV video, and route
>them to a
>LAN - and thereafter extract the contained data on the client
>machines.
>>From what I understand, this simply involved demuxing the MPEG TS and
>feeding it to a perhaps modified Linux TCP stack?  Is there
>support for
>this in the current version of the DVB software?
>
>Keith
>
>On Fri, 19 Jan 2001 Rod.Walsh@nokia.com wrote:
>
> > ATSC uses VSB8 modulation so you'll need a new tuning
>driver (just the same
> > for DVB-T which uses OFDM+QAM/QPSK) - note DVB-S which uses QPSK.
> > (Practically this is compiling with new or improved
>frontend.c and .h)
> >
> > Some of the DVB and ATSC SI tables are common (because they
>are both based
> > on MPEG TS) and some are different so here's another place
>for work (VDR
> > guys?).
> >
> > I am not an ATSC expert so I can't tell you exactly how
>ATSC encapsulates
> > IP, but I guess you'll be needing modifications to demux.h and more
> > significant ones to demux.c (as you might expect).
> >
> > Naturally, it would be great if the same API handled all
>DTV methods (anyone
> > interested in the Japanese system?) so thanks to those who want this
> > challenge.
> >
> > Good luck!!!
> > Rod.
> >
> > PS For those confused: ATSC is the North American
>'equivalent' for DVB-T.
> > DVB-T is the terrestrial (i.e. standard antenna) version of
>DVB - the rest
> > you can work out for fun :)
> >
> >
> > > -----Original Message-----
> > > From: ext Ralph Metzler [mailto:rjkm@convergence.de]
> > > Sent: 19 January, 2001 4:43
> > > To: Keith Craigie
> > > Cc: linux-dvb@linuxtv.org
> > > Subject: [linux-dvb] ATSC/DTV question
> > >
> > >
> > > Keith Craigie writes:
> > >  > Hi there,
> > >  >
> > >  > Now I know this is the DVB mailing-list ... but now that
> > > ATSC is more
> > >  > available, is there plans to start a parallel project on
> > > linuxtv for
> > >  > supporting the American standard?  Also, if anyone knows
> > > any links to
> > >  > projects/mailing lists for ATSC, I'd appreciate their
> > > passing them on.
> > >
> > > According to the ATSC specs, it looks similar enough to DVB
> > > that a lot of
> > > the DVB software can be reused for ATSC.
> > > There are some differences in the hardware as well as the
> > > specifications
> > > for service information. But I see no reason why the DVB
>API we are
> > > using for our driver could not be used for ATSC as well.
> > > I would welcome any discussion on this.
> > >
> > > Ralph
> > >
> > >
> > > ---
> > > Info:
> > > To unsubscribe send a mail to listar@linuxtv.org with
> > > "unsubscribe linux-dvb" as subject.
> > >
> >
> >
> > ---
> > Info:
> > To unsubscribe send a mail to listar@linuxtv.org with
>"unsubscribe linux-dvb" as subject.
> >
>
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