[linux-dvb] pid filtering

[Marcus Metzler <mocm@metzlerbros.de>]

Harald Dankworth writes:
 > I have some problems with the mpeg-2 mpts to mpeg-2 spts filtering in the
 > linux driver with a WinTV Nova card; during playback it seems like the pcr
 > is not correct. The playback is choppy if the demultiplexer does not support
 > resampling for correction of the pcr.
 > 

With what program/hardware. The av7110 does not check PCRs when doing
playback and most software player don't do that either. They just use
the PTS for synching.


 > According to ISO/IEC 13818-1 page xiii:
 > "Figure 0-3 illustrates the second case, where a transport stream containing
 > multiple programs is converted into a transport stream containing a single
 > program. In this case the remultiplexing operation may necessitate the
 > correction of program clock reference (pcr) values to account for changes in
 > the pcr locations in the bit stream."
 > 
 > Thus, if the dvb driver drops packets from the mpeg-2 mpts there pcr should
 > be restamped. There is one paper covering the problem:
 > http://cairo.cs.uiuc.edu/HD/mse2002.pdf

The kernel only does the filtering not the remultiplexing. And it is
not a multiple program TS (mpts I guess but should not have to) 
to single program TS filtering, it is a simple PID filter. The rest
has to be done in userspace. The kernel cannot be responsible for the
internals of the transport stream, because otherwise it would have to
check all the filters that are open in order to see if there is a
certain service which is filtered and than adjust the clock values for
that service. E.g. if you only filter the audio stream of a program,
you usually won`t even get a PCR.

 > 
 > Has anybody any thoughts about this?
 > 

There could be a new type of filter which filters a certain
service or as you said mpts to spts. This would require the kernel to
check the PAT and PMT and get all the PIDs belonging to the
service. Then it has to adjust the tables and clocks accordingly.
IMHO this is probably not a job for the kernel, unless there is a
hardware solution.

Marcus

-- 
/--------------------------------------------------------------------\
| Dr. Marcus O.C. Metzler        |                                   |
|--------------------------------|-----------------------------------|
| mocm@metzlerbros.de            | http://www.metzlerbros.de/        |
\--------------------------------------------------------------------/



-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.