[FFmpeg-user] Problem with vf pad ... help please

[Emre Karataşoğlu]

did you try this?
-vf="scale=x:y,pad:W:H:PadX:PadY"

2012/9/17 Mark Himsley <mark at mdsh.com>

> On 17/09/2012 17:53, Tim Nicholson wrote:
> > On 17/09/12 16:36, Nicolas George wrote:
> >> Le jour de la Vertu, an CCXX, Mark Himsley a écrit :
> >>> You are falling into the trap that the all of the pixels on a 720x576
> >>> line are part of the active 4:3 picture. Where as only 702 pixels are.
> >>>
> >>> If you wish to ignore the calculated scale and pad values I gave you
> >>> above, and insist on sticking with your calculated numbers, then you
> >>> (like many before you and many to follow) will get the will get the
> >>> images 2.5% too narrow. I'm sure that will flatter most people, being
> >>> 2.5% too thin, but it is wrong. Please believe the experience of 26
> >>> years at the BBC.
> >>
> >> Do you have any normative reference about that? It seems to contradict
> what
> >> I remember (I'll have to dig into the standards again) reading.
> >>
> >
> > You have to work it out from ITU-R BT.601-7 TABLE 4 and ITU-R BT.470-6 !
> >
> > This gives (for 625/50):-
> >
> > Number of samples per total line for each signal =864.
> >
> > Analogue total line timing 64us
> > Analogue active line timing 52us
> >
> > Therefore digital samples per active analogue line = 864*52/64 =>702.
>
> Or to put it another way.
>
> The sample frequency of an analogue 'PAL' or 'SECAM' line is:
>
> 1 / 0.000064 * 864 = 13.5 MHz exactly.
>
> Which makes the active 52 micro-seconds have exactly 702 pixels
>
> 0.000052 × 13500000 = 702
>
> I've heard people say that the size of a digital line is different to
> the size of an analogue line. But that is not how it was (is, for those
> places which have not gone all digital yet) transmitted, so is a wrong
> assumption.
>
> > The 4:3 aspect ratio dates back to analogue days and so aspect ratio
> > calculations must be based on the analogue picture width and height, i.e
> > 702x576.
>
> Exactly.
>
> > Hope this helps.
>
> Yes - it saved me a lot of typing. Thanks Tim.
>
>
> I think I'd like to submit
> http://lipas.uwasa.fi/~f76998/video/conversion/ as evidence too, as
> Jukka has a good way with words and a good selection of references.
>
> --
> Mark
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