[vdr] Re: [PATCH] (DVB-T) statmux fix vbr tagging for pic header

["Wiljo Heinen" <wiljo@offeryn.de>]

Hi !

>
> How do you detect whether a stream is VBR in PVAStrumento? Do you look at
> bitrate changes between headers - but then again those could be set to CBR
> as you point out in the helpfile. Does this mean when "Flag Stream as
> variable Bitrate stream" is set it always sets the vbv_delay to 0xFFFF
even
> for proper CBR files? I take it, it can't have a negative impact for the
> decoder then (as underflows are allowed but not overflows)?
>

If the option is set, PVAStrumento sets the vbv_delay to 0xFFF -
it does not inspect the data.

Anyway - the concept of CBR is really not easily applicable to
MPEG2. See for instance what the standard (13818-2) says
in section D.9.11 ("Bit_rate and vbv_delay" - difference between
MPEG1 and MPEG2):

"MPEG-2 - The semantics for bit_rate are changed. In variable bitrate
operation, vbv_delay may be set to FFFF (hex), but a different value does
not necessarily mean that the bitrate is constant. Constant bitrate
operation is simply a special case of variable bitrate operation. There is
no way to tell that a bitstream is constant bitrate without examining all of
the vbv_delay values and making complicated computations.
Even if the bitrate is constant the value of bit_rate may not be the actual
bitrate since bit_rate need only be an upper bound to the actual bitrate."

So - I just guess, setting all vbv_delay values to 0xFFFF should do no
harm....

Regards

    Wiljo




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