'Max_Rebo's guide to resizing lettebox to anamorphic pal', or 'where the values were pulled from'.
lets start by having a look at the sources:
The movie on disc 1 in anamorphic 2.35:1 PAL with Dolby Digital 5.1 at 384kbps.
The deleted/extended scenes on disc 1 in letterboxed 4:3 PAL with Dolby Digital 2.0 at 192kbps.
The deleted/extended scenes on disc 2 in anamorphic 16:9 PAL with Dolby Digital 2.0 at 224kbps.
so lets see, the easiest way is to count pixels as I suggested, for 16:9 anamorphic PAL I believe the standard is to have both black bars at 74-76 pixels e.g. from my current project:
(I hope this also explains why my photoshop font is set the way it is)
so...
Serenity main feature:
not quite what I was expecting, is this truely representative of the whole film? i.e. past the openning credits, still it's a good example because the lack of symmetry makes it a challenge.
scene from disc 2
The disc 2 scenes seem to be in the same aspect ratio as the movie (don't know how to be sure though)
so saddly this is a bit out and will need fixing if there is any hope of it fitting into the main feature else the bars will jump when these scenes begin and end.
so here is how we get the numbers, I hope you like maths!
first the virtical resolution of pal is 576, so deduct what is used by the bars in the main film (our reference)
576-74-66 = 436
do the same for the disc 2 scene: 576-80-75 = 421
so we need to stretch 421 to become 436, the ratio of these values is 436/421 = 1.036
we need to know how many pixels will, when stretched by this amount, make up the full resolution of pal so devide 576 by the ratio: 576/1.036 = 556
so the amount of pixels that need to be cropped before resizing is 576-556 = 20.
now if we were dealing with symmetric bar it's easy crop 10 off the top 10 off the bottom and resize to 576, but they're not symmetrc so it's not that easy!
now the fun begins, the ratio of the bars in the main film is 74/66 = 1.12121212
so we need the same ratio in our stretched frame, so we set up some simmultaneous equations
80-x = 1.12121212
75-y
where x is the pixel to be cropped from the top and y is the pixels to be cropped from the bottom so we know x+y = 20 the total number that need cropping.
to solve this substitute y=20-x into the first equation giving:
80-x =1.12121212
75-20+x
multiply across to give:
80-x = 1.1212(75-20+x) then rearrange:
80-x = 1.12(55) +1.12*x
80 = 1.12(55) +2.12*x
80-1.12(55) = 2.12*x
solving this for x gives x = 8.64 and since y=20-x y=11.36,
so rounding the numbers we now know we have to crop 9 pixels from the top, and 11 from the bottom, so using vdubmod resize to the same size then set these crop values so the filter line reads:
720x556 720x576 resize(lanczos3)
and the result will be:
save this as an avi and then encode as anaorphic pal this scene should now fit nicely into the main film without any change in aspect ratio.
part 2, 'letterbox to anamorphic' comming soon.