4:3 DVDs with Different DARs

[Skiller]

@ Sharc
Hmm I don't understand. Example 5) in post #46 is already at 720x480. Why would this get resized at all by AVS2DVD or DVDStyler and how would they know if it needs resizing?

[Sharc]

@ Sharc
Hmm I don't understand. Example 5) in post #46 is already at 720x480. Why would this get resized at all by AVS2DVD or DVDStyler and how would they know if it needs resizing?

The active picture of example 5) is 704x480, PAR 10:11. It has been padded to 720x480 (using 2x8 pixels green pillars instead of the usual black), which simulates an analog mpeg4/ITU capture of 704x480 active plus 2x8 side pillars to make it 720x480 full frame. The PAR is still 10:11 though because padding does not change the PAR.
If one does not crop the green side pillars off, the DAR of the full frame including the green side pillars should be 15:11 (1.364) rather than 4:3 (1.333...) in order to display the active picture undistorted.
AVS2DVD and DVDStyler do not crop the green side pillars off for 4:3 playback or stretch the picture horizontally, but shrink it vertically and pad it top and bottom to make the full frame 720x480 again. The AR of the source picture of example 5) including the green side pillars then becomes 15:11 (1.364), and the active picture (excluding green side and black top/bottom bars) is exactly 4:3, means circle and square is undistorted.
Of course this works only if the source has the correct PAR signalling (10:11 in this case). Apparently the PAR is read by AVStoDVD and DVDStyler, either from the stream or from the container I don't know. Also I did not try for other containers. I was just curious how these DVD authoring tools would handle example 5). Snapshot of the .VOB attached; full frame including all borders is 4:3; gray part (=active picture) is 4:3 as well, no distortion.

Added: The second attachement shows the frame as stored in 720x480 full frame .vob, viewed as square pixels.

[Skiller]

Thanks for the explaination, Sharc. Now I understand what and why it's happening. And I understand it would only happen with something like an MKV that has SAR signaling.

So what this essentially does is it converts ITU PAR to Generic DAR; but in a less common way, by shrinking vertically. Personally, I consider this conversion by itself (in whichever way) as "kinda" wrong. Kinda because both can be right and wrong depending on the playback conditions. It sure would be wrong when the DVD of example 5) is played back through some analog connection (picture gets 2.5% wider, or rather vertically compressed). On the other hand, it would be an actual correction for when the DVD is played back through HDMI or most software players on a computer where for the entire 720x480 frame DAR=4:3 is used. So, yeah, the usual problem of which standard applies depends on the playback conditions.


The solution is to encode at a width of 704 and thereby removing the ambiguity and have the exact correct aspect ratio no matter where it's played. This works perfectly for titles. The problem with menus on DVD is, you really have to use a width of 720. I tried 704x576 menus but the button highlights (subpics) on some players are horizontally shifted then – so it's useless.

I make my DVD menus at 1048x576 or 786x576 and then resize that to 720x576 and encode to MPEG2 myself so that authoring softwares don't do any encoding on their own.