[FFmpeg-devel] [PATCH 2/3] lavd: add teletext quantizer

Marton Balint cus at passwd.hu
Thu Jan 14 21:33:36 CET 2016

On Wed, 13 Jan 2016, Michael Niedermayer wrote:

> On Wed, Jan 13, 2016 at 05:01:01AM +0300, Andrey Turkin wrote:
>> Why not use libzvbi's slicer? It should be pretty robust with
>> less-than-ideal signal.
>> Regarding your code - is there a need to calculate a frequency? I did
>> something similar a while back with VBI from TV signal and in my experience:
>> a) this kind of frequency/phase estimation doesn't work that well on a
>> noisy signal.
>>  b) there's really no need to estimate frequency - it's a known constant
>> (well it depends on a standard but in each standard it is a constant) and
>> generators usually don't deviate from it; you just need to get a good phase
>> estimation based on, say, local maxima/minima of run-in bits.
> to calculate the phase


Thank you all for the comments and suggestions, I have learned a lot from 
it. The reason why I did not use libzvbi was not licensing, I simply 
wasn't sure at first that this can be done conveniently with it, and 
instead of checking the docs, writing it from scratch was more fun.

Anyway, now I know that I can almost seamlessly replace the 
teletext_qunatizer stuff with libzvbi's vbi_bit_slicer, so I will rework 
the patch series to use that. The higher level interface of libzvbi - 
vbi_raw_decoder seems too high level (bloated) for my use case.

As for the licensing, I believe now that libzvbi is LGPL because it 
references the GNU Library General Public License wich is the predecessor 
of the LGPL, so I will submit a patch to remove the GPL depdendency from 
libzvbi as well.


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