[linux-dvb] Re: SI_PARSER.C ISSUE

[Sheetal_Pandey <Sheetal_Pandey@Satyam.com>]

Hi Rolf,

You are correct that the EN300468 doesnot talk about adaptation field
because it is oriented towards DVB standard.Adaptation field concept comes
in MPEG2 Transport streams.I will send you the code for review once it is
ready.

I have some clips as I mentioned in my first mail, where the 5th byte after
the header gives the info about the offset of the setion.My query is that
does the real time stream has the same syntax or not because you must have
tested your code on them.Pl. find below a PAT packet which explains what I
meant.

<--------------------188
bytes------------------------------------------------------------->
47 40 00 10 00 00 B0 11 00 01 C1 00 00 00 00 E0 10 00 01 E0 64 F3 1E 15 01
FF...........FF

Regards,
Sheetal Pandey


-----Original Message-----
From: Rolf Hakenes [mailto:hakenes@hippomi.de]
Sent: Sunday, February 16, 2003 4:27 PM
To: Sheetal_Pandey@satyam.com
Cc: linux-dvb@linuxtv.org
Subject: Re: SI_PARSER.C ISSUE


Hi,

sorry for this late reply, but I have been on a business trip last week.

You are right. The si_parser.c code does not take care of adaptation
fields at the moment. As far as I know, adaptation fields are only
relevant for the MPEG stream layer (like the video, audio or SI stream),
whereas si_parser.c deals with MPEG system information (SI) layer only.
In my point of view this is another (higher) protocol layer. I think the
driver code deals with the adaptation fields during filtering the
sections out of the MPEG data stream, because I never had any problems
with that.

If I did something wrong, I would be very happy to integrate or fix that
within the code. Please send your corrected si_parser.c to me, so that I
could have a look at it.

Additionally, I do not see any adaptation fields defined in EN 300468,
beside the notice, that instead of using stuffing tables to fill unsused
data stream regions, the adaptation mechanism could be used for this
purpose as well. But that is quite obvious, as stuffing tables are the
stuffing mechanism provided by the DVB-SI protocol layer, adaptation
fields are the stuffing mechanism provided by the underlying protocol
layer, and of course you are free to use either of them to stuff your
data... 

Geetings,

Rolf

> 
> Hi Rolf,
> 
> I want to bring under your notice some of the points that I had found
out
> during the development.I am referring the document
> DVB-SI_info-en_300468v010401p for extracting various tables from TS
> clips.This document can be downloaded from etsi.org which is an
official
> site for DVB documents.
> 
> Pl. see that my findings are based on above document which talks about
the
> syntax of MPEG2 TS.
> I found that the code si_parser.c doesnot take care of the ADAPTATION
FIELD
> CONTROL bits.To explain a little further, in the header there are two
> adptation field control bits which has following options:
> 
> 1.01-no adptation field,payload only
> 2.10-adaptation field only,no payload
> 3.11-adaptation field followed by payload
> 4.00-reserved for future use.
> 
> Since the code need to be general it should take care of all the four
> options.The presence of an adaptation field is indicated by the
adaptation
> field control bits in a transport stream packet.If present,the
adaptation
> field directly follows the 4 Byte packet header,before any user
payload
> data.This is the case with the clips I have.
> 
> I had modified the si_parser.c to consider these bits.I would highly
> appreciate if you can comment on this.
> 
> Regards,
> Sheetal Pandey
> 


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