[linux-dvb] Re: Section Filters

[Rolf Hakenes <hakenes@hippomi.de>]

Hi,

many thanks for your additional documentation, but after experimenting a
bit with this type of filter you described I found, that not only byte 1
and 2 are uncovered by the filter, but byte 3 and 4 are ignored as well.
Therefore byte 2 of the filter array means the section number and byte 1
contains current/next indicator at bit position 0. Is this
interpretation correct, or am I tricked by a strange behaviour of the
datastream ?

Best regards,

Rolf Hakenes

Johannes Stezenbach wrote:
>
> Rolf Hakenes wrote:
> >
> > I'm experimenting with the DVB-SI datastream for quite a long time now in
> > order to extract useful information out of it. Dealing with this some
> > questions came up concerning the meaning and usage of the API built-in
> > section filter mechanism. Both APIs provide (theoretically)  the possibility
> > to define a mask value on a specified TID as well as multiple TIDs (up to 16
> > AFAIK) per filter. Unfortunately I was not able to get any working setup for
> > a filter using these (undocumented) features. Therefore I'd like to ask
> > someone (who possibly knows) about the meaning and implementation status of
> > the described fields of the filter structures.
> 
> Here's what's missing from the documentation of the demux device
> of the new API:
> 
> --------
> The dmxFilter structure defines a section filter, i.e. a bit pattern
> and a mask for the first bytes of a section. The filter comprises
> 16 bytes covering byte 0 and bytes 3..17 in a section, thus excluding
> bytes 1 and 2 (the length field of a section).
> 
> The mask states which bits to be used for filtering, and the filter
> states the actual value of these bits. Only the value of the bits
> where the corresponding mask bit is 1 will be checked.
> --------
> 
> Byte 0 in the filter is the table id.
> 
> 
> Johannes
>


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