Downconversion to non-widescreen NTSC DVD?

[striker9]

Let's say that I start with 720p video (square pixels) and I want to crop it then convert to 4:3 NTSC DVD. Should I crop to 960x720 or 1080x720 before conversion? The 960x720 has the correct 4:3 display aspect ratio but incorrect storage aspect ratio for a DVD. The 1080x720 has the correct storage aspect ratio (3:2) but incorrect display aspect ratio.

I know you can't get both the correct SAR and DAR for the source when converting from square to non-square pixels, but which one should I have correct before conversion to get the best quality?

The problem is that I don't know how conversion programs deal with the pixels. Can they just shrink a square pixel to a non-square pixel? I'm pretty sure that if I were making a 16:9 DVD that I would want to start with a source that has 16:9 DAR rather than "elongating" a 3:2 DAR. But because 4:3 is so close to 3:2, it seems it might be better to just start with a source with a 3:2 DAR (with square pixels) and "shrink" the pixels down.

Any help would be appreciated.

Thanks

[edDV]

Why crop to 4:3 when you could preserve the 16:9 by resizing 1280x720 to 720x480 and make a wide DVD?

To do a 4:3 crop correctly you would crop to 960x720, then resize that to 704x480. For 720x480 you would crop 982x720 (720/704x960 = 982) before downsize to 720x480.

[manono]

...but which one should I have correct before conversion to get the best quality?

You get the best quality by making a 16:9 DVD out of it, leaving it uncropped.

But because 4:3 is so close to 3:2, it seems it might be better to just start with a source with a 3:2 DAR (with square pixels) and "shrink" the pixels down.

When resizing you do it all in one step with no intermediate resizing done.

[striker9]

Why crop to 4:3 when you could preserve the 16:9 by resizing 1280x720 to 720x480 and make a wide DVD?

It's just a theoretical question to help me understand it better. I haven't included all the details of what I plan to do.

To do a 4:3 crop correctly you would crop to 960x720, then resize that to 704x480. For 720x480 you would crop 982x720 (720/704x960 = 982) before downsize to 720x480.

I don't understand. Why would a 960x720 crop be properly resized to a 704x480 but not a 720x480 DVD? Both 720x480 and 704x480 DVD have a 4:3 DAR. It's just the pixel aspect ratio (pixel shape) that differs. Perhaps you could provide a reference or explain further.

Thanks

[striker9]

When resizing you do it all in one step with no intermediate resizing done.

If I want to crop a specific portion of the video (that has action going) then I have to do it manually. In some instances, I may want to crop different sections of the video at different times. I'm mostly talking about stuff I might shoot myself.

[manono]

If I want to crop a specific portion of the video (that has action going) then I have to do it manually. In some instances, I may want to crop different sections of the video at different times. I'm mostly talking about stuff I might shoot myself.

Yeah, so? I said nothing about cropping, only resizing. Crop each part any way you like followed by the final resize. But if you have to do much cropping, it seems to me you'd have been better off getting a video camera that shoots 4:3 in the first place.

I don't understand. Why would a 960x720 crop be properly resized to a 704x480 but not a 720x480 DVD? Both 720x480 and 704x480 DVD have a 4:3 DAR. It's just the pixel aspect ratio (pixel shape) that differs. Perhaps you could provide a reference or explain further.

3.2.1 640×480 "industry standard" square pixels to 720×480 ITU-R BT.601 pixels (Edit: Or your same ratio 960x720 example)

Let's say I have captured a video clip from 525/59.94 source using an old M-JPEG card that only allows sampling in "industry standard" (12 + 3/11 MHz) square pixel format. The resolution of the clip is 640×480. Now I would like to incorporate this into a DV project that uses ITU-R BT.601 pixels and a resolution of 720×480.

The first step is to look up the correct source and target formats from the table.
In this case, the source format is 640×480 in a 525/59.94 system, using the sampling rate of 12 + 3/11 MHz and a pixel aspect ratio of 4752/4739.
The target format is 720×480 (likewise in 525/59.94 system), using the sampling rate of 13.5 MHz and a pixel aspect ratio of 4320/4739.
The second step is to calculate the vertical conversion factor. In our case, it is 486/486 = 1
Now we need a horizontal rescaling factor, which in this case is (4752/4739) / (4320/4739) * 1 which equals to 11/10.
Then we can calculate the new image width from the old one: 11/10 * 640 = 704 pixels
The image height will stay unchanged, since 1 * 480 is still 480.
Thus, we need to resample the 640×480 image to 704×480.
However, our original target resolution was 720×480. Now we need to pad the image (with black vertical bars on the side) so that the frame width will become 720 pixels. A natural conclusion is that we need to add 8 pixels black to both side edges.

http://lipas.uwasa.fi/~f76998/video/conversion/

[striker9]

Strangely enough, I remember reading that link before. It's still a little over my head.

This is what I'm getting from your responses though. If I want to convert ANY video with square pixels (regardless of whether it's SD or HD) to 4:3 NTSC DVD at 720x480, then I want to actually have a DAR in the source material of approximately 4.09:3. And this holds true regardless of which converter I'm using?

Thanks.

[edDV]

Strangely enough, I remember reading that link before. It's still a little over my head.

This is what I'm getting from your responses though. If I want to convert ANY video with square pixels (regardless of whether it's SD or HD) to 4:3 NTSC DVD at 720x480, then I want to actually have a DAR in the source material of approximately 4.09:3. And this holds true regardless of which converter I'm using?

Thanks.

PAR for 704x480 and 720x480 is the same 0.9091. 720x480 is just wider by 16 pixels.

Many ignore this for wide DVD and just resize 1280x720 directly to 720x480. The aspect ratio distortion is slight.

If this was intended for ATSC broadcast 480i/p wide, you would resize to 704x480. All ASTC SD video is 704x480, even wide.

[manono]

As edTV showed, there are ways to crop your 1280x720 source so that you can resize to 4:3 720x480 correctly. But yes, if starting with some square pixel 1.33:1 source, for DVD it should be resized to 704x480. This isn't to say that all DVD production companies do it correctly. This isn't even to say that if you convert to a full 720x480 you'll be able to tell the difference. It's just to say that if you want to do it correctly you should resize to 704x480, maybe padding out to a 720 width with black bars.

[striker9]

Okay, thank you. I think I understand.

My initial question had to do with whether I should have source material with a 3:2 or 4:3 DAR. You've answered that.

I doubt whether a small percentage variation from 4:3 will make much of a difference in the appearance of the final product anyway. I do want to create 720x480 video to make sure that my mpeg-2 videos are also compatible with Blu-ray specs. 704x480 is not compatible.

My only concern is whether the converter I'm using would "prefer" to have a specific DAR ratio in the source material to create the best appearing video. My guess would be no.

I'm open to any more discussion on the topic, but my take is that somewhere in the neighborhood of 4:3 source video will create the best results, but it doesn't have to be exact.

Thanks again.

[edDV]

If you intend SD Blu-Ray, or DVD release, use the 982x720 crop downsized to 720x480. That would be correct after a 704x480 ATSC crop as well.

[striker9]

If you intend SD Blu-Ray, or DVD release, use the 982x720 crop downsized to 720x480. That would be correct after a 704x480 ATSC crop as well.

Okay.

Thank you.