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

Andrea Venturi a.venturi at cineca.it
Tue Oct 3 11:29:20 CEST 2006


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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