Is 704x480 with a 16:9 DAR valid for DVD?

[intracube]

I think that with the sequence_display_extension it might be the case that if it is not set the entire frame is taken as the picture area -- we knew this for sure already -- but if it is set, then it is set to 720x480 (for NTSC widescreen)

I'm not sure what the purpose of that would be. The theory put forward on this thread (based on iso13818-2) is that the sequence_display_extension would be used only if the active picture area differed from the total frame area.

if it is not set the entire frame is taken as the picture area -- we knew this for sure already

My own view is that this isn't confirmed - there's still conflicting information.

This whole area feels 'messy'. For example, as most digital video systems use 704x480 as the 'active' picture area - if the DVD standard really is different, then broadcast recordings would have to be:
- Rescaled to 720x480
- Encoded to a 704x480 mpeg stream
Resizing/re-sampling should be avoided wherever possible - it often introduces artifacts/softens the image or both. Why would the people who defined the DVD standard break away from established standards?

Or you can argue that the producers of DVDs ignore the MPEG 2 spec

It's a shame the official spec. is so hard to come by. The 'DVD-Video Book' costs thousands, and it has a non-disclosure agreement attached. I think it's pretty poor that an organization would make it that difficult for people to understand the spec. and share the information with others.

I haven't yet found a 720x480 disc that has a sequence_display_extension of 704x480. Would you let me know if you find one that does?

GSpot works with wine - so I can quickly go through my DVDs.

BTW, this topic has already been discussed:
https://forum.videohelp.com/threads/236536-720-vs-704

[Anonymous344]

I'm not sure what the purpose of that would be.

I'm not sure either. I'm just trying to make sense of what I see.

GSpot works with wine - so I can quickly go through my DVDs.

Thanks for that! I agree with what you wrote about the DVD spec.

[intracube]

Here are some of the DVDs I've tried tonight.

Ripped the beginning of each DVD to disk with:
mplayer -dumpstream dvd://1

then analysed with GSpot.

Note: a significant number of the DVDs don't fill the full width of the frame.

Star Trek Generations
16:9 720x576
no sequence_display_extension

Star Trek Insurrection
16:9 720x576
no sequence_display_extension

The Fast Show Series 2
4:3 720x576
sequence_display_extension = 720x576

From Russia With Love
16:9 720x576
sequence_display_extension = 720x576
* GSpot reports aspect ratio as 4:3

Goldeneye
16:9 720x576
no sequence_display_extension

The World Is Not Enough
16:9 720x576
sequence_display_extension = 720x576
* GSpot reports aspect ratio as 4:3

Jurassic Park: The Lost World
4:3 720x480
sequence_display_extension = 720x480

Flightplan
4:3 720x480
sequence_display_extension = 720x480

Terminator 2: Judgement Day
16:9 720x576
sequence_display_extension = 540x576

[jagabo]

Note that 540x480 or 540x576 4:3 pan and scan implies the full frame is 16:9. 4:3 * 720 / 540 = 16:9

[Anonymous344]

Note: a significant number of the DVDs don't fill the full width of the frame.

Thanks for the list! That is what I meant before: the DVDs do not fill the frame, from which one might deduce that the picture is contained in the 704x480 area, but they are flagged 720x480 in sequence_display_extension. If there is no extension, then the whole 720x480 frame is image, but if there is an extension, it is written as 720x480 rather than 704x480 (for NTSC widescreen). I do not think we will find a 720x480 DVD with a sequence_display_extension of 704x480. (I could of course be wrong though.)

[jagabo]

I do not think we will find a 720x480 DVD with a sequence_display_extension of 704x480. (I could of course be wrong though.)

I haven't seen any out of the few dozen I've checked since learning about the SDE. I've also never seen a commercial DVD at 704x480/576.

[Anonymous344]

Thanks, Jagabo!

HC Enc 0.25 writes 704x480 as the sequence_display_extension for actual 704x480 DVDs, if you specify colorimetry. I will have to check some commerical 704x480 DVDs and see if they have 704x480 for sequence_display_extension too.

[Alex_ander]

One more tool dealing with SDE: ReStream utility.

[Anonymous344]

Thank you, Alex_ander. Restream has already been discussed.

What I don't understand is if 704x480 is valid for DVD why commercial DVDs are padded to 720 rather than just authored as 704x480 DVDs.

[manono]

What I don't understand is if 704x480 is valid for DVD why commercial DVDs are padded to 720 rather than just authored as 704x480 DVDs.

They aren't all. I've seen dozens of them at 704x480.

[Anonymous344]

They aren't all. I've seen dozens of them at 704x480.

I agree. There certainly are some, but most I've seen are 720x480 with blanking. It would seem more logical not to encode the blanking at the sides.

[Alex_ander]

I haven't yet found a 720x480 disc that has a sequence_display_extension of 704x480.

Did you look for it with GSpot? It was a big surprise for me when it displayed 720 in extension instead of 704 written in ReStream. Imported back into Restream, it read 704!
Considering pan & scan usage (540), which is only activated by a player at AR conversion for different display type (4:3), the SD extension is unlikely used by DVD in common case. So it looks like the player must always use actual pixel numbers for written AR (by H.262, without following BT.601).

[Cornucopia]

That's why I've been saying for a while now that Gspot has flaws.

<rant>(Doesn't anybody get that there is NO SUCH THING as "Storage Aspect Ratio"? It's just stored vertical & horizontal resolution - that's all!! You'll never see SAR refered to in any SMPTE or Broadcast specs or whitepapers, just DAR or PAR.)</rant>

Scott

[jagabo]

<rant>(Doesn't anybody get that there is NO SUCH THING as "Storage Aspect Ratio"? It's just stored vertical & horizontal resolution - that's all!!

They are the same thing, just different terminology. It's much easier to write/read "SAR" than "stored vertical & horizontal resolution". Especially when you're writing it as a mathematical equation:

DAR = PAR * SAR

It's unfortunate that some people use SAR to mean storage (frame size) aspect ratio (as above) and others use it to mean pixel aspect ratio (as in x264). I usually specify which I mean when I use the term.

[Gavino]

(Doesn't anybody get that there is NO SUCH THING as "Storage Aspect Ratio"? It's just stored vertical & horizontal resolution - that's all!!

Personally, it's PAR (and talk of 'square' and 'non-square' pixels) that annoys me, although I recognise it's a lost battle now.

See Alvy Ray Smith's classic 1995 paper: A Pixel Is Not A Little Square.
(In summary, a pixel is a point sample - it exists only at a point, so the 'correct' terminology is pixel spacing ratio.)

[jagabo]

a pixel is a point sample

That's really only true in certain theoretical and abstract circumstances, like ray tracing. In the real world photo receptors have a finite size and geometry, they are not infinitely small points. And it still makes sense to talk about pixel aspect ratios when you instantiate a pixel, on paper or on a monitor where the pixel will have a size and aspect ratio. DAR = PAR * SAR is still useful.

[Gavino]

In the real world photo receptors have a finite size and geometry, they are not infinitely small points. And it still makes sense to talk about pixel aspect ratios when you instantiate a pixel, on paper or on a monitor where the pixel will have a size and aspect ratio.

Yes, but even then, the physical shape of sensors and display elements is rarely rectangular.
In terms of sampling theory (necessary to properly understand how resizing works), the pixel values represent point samples.

DAR = PAR * SAR is still useful.

Certainly, but "pixel spacing ratio" would be a more accurate name.
However, the terminology is now so widespread it's pointless arguing about it.