[M4IF Technotes] confusion about modulo_time_base, vop_time_increment, ...

[Arcin Bozkurt]

> -----Original Message-----
> From: technotes-admin   lists.m4if.org
> [mailto:technotes-admin   lists.m4if.org]On Behalf Of Christoph Lampert
> Sent: Wednesday, August 07, 2023 10:53 AM
> To: technotes   lists.m4if.org
> Subject: RE: [M4IF Technotes] confusion about modulo_time_base,
> vop_time_increment, ...
>
>
> Hello,
>
> thank you for your answer. I have one small additional
> clarification to
> ask for:
>
> On Wed, 7 Aug 2002, Arcin Bozkurt wrote:
> > I will be answering your questions in a different order and
> hopefully will
> > be clear. I will write my interpretation and how I am doing it.
> >
> > You are right, modulo_time_base in normal circumstances
> will never be two.
> > You can create a setup where it will be, but it would not
> be very realistic
> > I believe.
> >
> > The only time modulo_time_base is non-zero, is when the
> real time completes
> > a one full second from the previous time a modulo_time_base
> was non-zero.
> >
> > Assume the simple fixed rate case: 30 fps. And the
> > vop_time_increment_resolution is 300. 300 means each tick
> is 1/300 seconds
> > long and the vop_time_increment is given as number of ticks in this
> > resolution.
> >
> > Your display times will be 0, 1/30, 2/30, 3/30, .... 29/30,
> 1, 31/30, etc.
> > In this case the values for modulo_time_base will be
> > 0, 0, (repeat 29 times), 1, 0 repeat 30 times), 1, 0
> (repeat 30 tiems)
> > and the Vop_time_increment will be
> > 0 10, 20, ... 290, 0 (this corresponds to a "1" in
> modulo_time_base), 10,
> > 20, ... 290, 0 , etc...
>
> That is what I expected, fine. However, this is just for
> I/P/S-VOPs, not
> for B-VOPs. Consider almost a sequence encoded with IBBPBBPBBP...
> and only 12fps to keep the lines shorter (vop_time_incr_res=120),
> I understand it would be (display order):
>
>  I   B   B   P   B   B   P   B   B   P   B   B   P   B   B   P
>  0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0
> 000 010 020 030 040 050 060 070 080 090 100 110 000 010 020 030
>
> now with 11fps (vop_time_incr_res=110) things get complicated.
> Would it be:
>
>  I   B   B   P   B   B   P   B   B   P   B   B   P   B   B   P
>  0   0   0   0   0   0   0   0   0   0   0   1   1   0   0   0
> 000 010 020 030 040 050 060 070 080 090 100 000 010 020 030 040
                                              ^^^
The Marked "B" is based on the P at 90. I would say what you wrote is
correct.
for the next one which is a P, it is also based on the same P at 90.