[linux-dvb] TS Stream - null packets generation?

Chun Chung Lo cclo at astri.org
Tue Oct 3 11:50:18 CEST 2006


Hi,

Thanks! You are right.

The model of the modulator is PROMAX MO-170. It can be configured to
Master mode (with null packet stuffing) and Slave mode (without null
packet stuffing). But I am not sure how to make it to operate in Slave
mode.

I also found the player is operating follows the PCR. I see there is a
CBR can be set, but when I set, the modulator reports it cannot lock the
signal (or frequency?).

Please help. Thanks.

Best regards,
Lo Chun Chung

-----Original Message-----
From: Andrea Venturi [mailto:a.venturi at cineca.it]
Sent: Tuesday, 03 October, 2006 5:29 PM
To: Chun Chung Lo; linux-dvb at linuxtv.org
Subject: Re: [linux-dvb] TS Stream - null packets generation?


Chun Chung Lo wrote:
> Hi all,
>
> I am now using a STB (under development) which its hardware
> configuration is:
>
> SAA7134 + TDA10046A + TD1316
>
> When I capture the TS stream (which is stream out by a DVB-T
> modulator), and compare the file with the original one, I found tones
> of NULL packets (which its header is 0x47 0x1F, 0xFF 0x10, and remains

> are 0x00 ... Until the end of a TS packets, 188bytes).
>
> The captured TS is corrupted in a random level, sometimes seriously,
> sometimes a bit.
>
> I found these null packets wasted lots of PCI bandwidth and, may these

> cause the above error?
>
> And where are the TS null packets come from?

hi,

usually, the DVB-T modulator fills the outgoing modulated TS with null
PIDs when the bitrate of the incoming TS is lower then the expected
outgoing bitrate.

 +----------+   +----------------+
 |          |ASI|                | UHF
 | TS player|---| DVB-T modulator|-----
 |          | IN|                | OUT
 +----------+   +----------------+

with expected i mean the useful bitrate that comes from the other
parameters you put in the DVB-T modulator:

- channel BW (7/8 MHz)
- FEC
- guard interval
- modulation (QPSK/QAM16/QAM64)

there are preformatted tables about it on the net.

then you should look at the TS player, you are using; it's feeding the
modulator at a constant bit rate (CBR) or it follows the PCR?

but you need to detail more thoroughly your setup if you want us to
better understand what's going  on.

anyway, i really don't know how it can be corrupted

bye



andrea venturi

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