You do yourself no favours by only quoting part of the relevant section. For the benefit of all, here is the whole relevant quote:
The EBU recommends that:
· In 625-line television systems sampled to ITU-R Rec. BT.601 part A, only the central 702 luminance
samples of the digital active line (samples 9-710 inclusive) and their associated chrominance samples
should be used to carry the active picture.
Note that this is not actually specific to DVD. More so that from what I read elsewhere DVD is based on 601. There is, as far as I am aware, no reference in 601 to 470 which, as the full page confirms that 601 only mentions 720 samples (pixels) and no reference whatsoever to 702/704.
And is there actually an ITU for DV ? The articles I read state that DV 'closely follows' 601 but since it is already a digital medium it can be independent of it. But the spec for DV, just like that for DVD, costs $$$$ so most have not read it and might even simply speculate as to what it contains.
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Like I mentioned earlier, 601 is an extension to 470, not made to superceed, but to extend it to digital realm.
601 mentions 720 samples, yes, but it mentions sampling rate of 13,5MHz. Now if we take 52 microseconds of active image line from 470 and sample it 13,5MHz, how many samples do we get? 702. Everything adds up.
There is no need for ITU for DV video, because DV video follows the ITU standard, just shoot BBC test pattents and transfer them to PC. DV follows ITU, as does DVD, for in order to be backwards compatible with analog systems based on 470 the DVD must be based on 601, which in practice means that it does everything specified in that attached EBU recommendation. Unless someone deliberetely authors DVD outside of those specs.
Because who sane would digitize a video tape that follows 470 with 601 specifications only to crop it to 702 and stretch to 720 to make a TV series DVD box-set? Noone at BBC for sure.
Ok. I get it. But for the sake of clarity I sought out some 'PAL Video for Morons' text:
But for me, and I guess most on here, life is too short to worry that dvds no longer STRICTLY follow ITU 601 (or at least the vertical blanking part of analogue PAL). The difference between 720 and 702/704 is so small that, as pointed out, most, without full knowledge of the original, would not see the difference. My own eyes (I do not have 20/20 vision) could not actually determine which of those circles were true - they both looked fine to me.
But if you want to spend your time creating ITU 601 strict dvds then it's your baby. But if you share these with people who have more 'modern' means to play and display them and spot some 'abnormality' do not think you were not warned.
Creating the ITU-compliant SD video is the easiest part, the tricky one is to modisy sequence display extension so that it would play properly on modern devices that were not properly engineered to be ITU/601 compliant, even if they are 709 compliant.
The most curious part is, when I make DVD from DV video, it uses the full 720 pixels, while still having 128:117 / 512:351 SAR, as per REC.601.
Another option would be to slightly crop top/bottom of the image to attain the corresponding DAR, which would result in modern devices playing it so that it does not have black bars and fills the display entirely, yet not wide enough and true image wold be displayed on ITU-compliant devices.
Out of curiosity: Have you been successful with manipulating the 'sequence_display_extension'?