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1) playing DVD on 4:3 screen
PAL DVD:
- video size in pixels: 720x576
- intended physical aspect ratio: 4/3
- pixel aspect ratio: 16/15
normal 4:3 computer screen:
- screen size in pixels: 1024x768
- physical aspect ratio: 4/3
- pixel aspect ratio: 1/1
-> scale to video size 720 . 16 / 576 . 15 = 11520 / 8640 = 144 / 108
= 4 / 3
2) playing PAL DVD on PAL TV
PAL DVD:
- video size in pixels: 720x576
- pixel aspect ratio: 16/15
=> intended display aspect ratio: 4/3
w/h = DAR/PAR (with w and h of pixel video size)
DirectFB PAL TV output:
- screen size in pixels: 720x576
- pixel aspect ratio: 16/15
=> display aspect ratio: 4/3
(v = video, source material - d = display)
DARv = DARd <=> wv / hv * PARv = wd / hd * PARd
<=> wd / hd = wv / hv * (PARv / PARd)
no scaling necessary
4) playing an NTSC vob on PAL TV
NTSC VOB (4/3):
- video size: 720x480
- pixel aspect ratio: 8/9
=> intended DAR: DAR = 720/480 * 8/9 = 80 / 60 = 4 /3
wd / hd = wv / hv * PARv / PARd
= 720/480 * 8/9 / (16/15)
= 720 * 8 * 15 / (480 * 9 * 16)
= 120 * 1 * 5 / (80 * 3 * 2)
= 15 / 12
= 5 / 4
--> 720 x ( 720 * 4 / 5) = 720 x 576
5) other examples
- 720 x 480, 32/27 on a square display
-> intended DAR: DAR = 720/480 * 32/27 = 80/3 * 1/15 = 16/9
keeping w constant:
720/h * 1/1 = 16/9 -> h = 720/16 * 9 = 45 * 9 = 405
keeping h constant:
w/480 * 1/1 = 16/9 -> w = 480 * 16 / 9 = 160 / 3 * 16 = 853.33
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