A Look Back Into 720 vs 704

[dellsam34]

I was reading some old threads here about 720 vs 704 and which one is better for the final encoded files after analog video capturing, The member edDV gave a good history about it here.

I capture from different sources (VHS, S-VHS, Betacam, PAL, NTSC...) and I find it hard to make a rule on which one to go for since some of the videos will loose some of the active video information if cropped all the way down to 704 with a fixed area of cropping (some videos have more black pixels on the right, some on the left). Cropping the 486 to 480 is a no brainer but I'm kind of lost when it comes to the horizontal resolution, I guess the old saying one size fits all doesn't really apply here.

Here are some of frame grabs of some projects I'm working on right now:

VHS NTSC


S-VHS NTSC


BetacamSP NTSC


VHS PAL

[petet]

More good info: https://en.wikipedia.org/wiki/Pixel_aspect_ratio

ITU-R BT.601 sampling rates at 13.5 MHz for 4:3 video gives 704 active pixels per line.

This why I personally keep raw copies and crop down to 704 and resize to 640x480 square pixels as I'm not working with any studio sources that have near that high of horizontal resolution. "NTSC VHS is roughly equivalent to 333×480" (https://en.wikipedia.org/wiki/VHS). Using a good scaling filter, you end up average out noise without needing to do any other type of noise reduction. This takes care of the black bar issue and relying on the player to respect your PAR/SAR/AR flags for distribution. You never want to throw information away if you have the space, but when you go for viewing copy, you break out all the cropping, filters, and compression for the subjectively 'best' viewing experience (I'm not making discs for anyone, file/streaming distro bias here)

[dellsam34]

I'm not sure about resizing to 640 but 704 seem to make more sense, I don't know how smart TV's and devices handle this weird resolution, I guess I will have to start trying it and see how it goes. What would be the ratio flag in the script?

[Sharc]

What capture cards actually do depends on the drivers and on the chipset, despite all standards and known PARs, DARs etc. One usually does not know the details about how the analog signal is captured, hence a general recommendation other than doing the circle test cannot be given IMHO.
Looking at your pictures I would say that the 3rd picture (BetacamNTSC) is stretched slightly horizontally. You should probably resize the active picture to 704 pixels horizontally and add left and right borders of 8 pixels width each to make it 720 overall in this case. It would also return the abc logo with a circular shape rather than an ellipse.

[dellsam34]

All images are stretched horizontally except the PAL one, that is because the aspect ratio flag is not active in jpeg picture file, But that's not the problem, The question is whether to crop the side borders to 704 or leave them alone as 720.

[Sharc]

Maybe I misunderstand the question. But I think 704 or 720 is your decision only. It will however depend on the standard you want to comply with.
720 with padding borders is compliant with the DVD and blu-ray standard and hence it is widely used. 704 width has some restrictions like not being blu-ray compliant for example, but there should be no problem with SW players, mp4 container etc. So it's entirely up to you. The rest is a matter of how you specify the PAR and DAR for the encoding.

[dellsam34]

No discs for me, being done with optical disc authoring years ago, though I have a large collection of Blu-ray and HD-DVD but that's about it, All captures are going to be HDD, memory or cloud, The master lossless copies on HDD off course.

[Sharc]

Well, in this case you are free to do what you like. You may leave the borders and keep 720 or you may crop to 704. Just keep an eye on the PAR (=SAR for x264/265) and DAR settings for the encoding process. Cropping will always preserve the PAR (Pixel Aspect Ratio, =SAR in x264/x265). Resizing will change the PAR (=SAR in x264/265). You can find tons of posts dealing with this subject.

[KarMa]

As jagabo has stated many times, according to the official DVD Video spec the entire horizontal picture should be active picture. So both 720 and 704 DVD should be considered entirely active video. Using this logic, cropping down to 704 from a 720 VHS capture would probably be the best for content destined for DVD. Obviously DVD is outdated but thought I would make the point.

I normally just leave the 720 for storage. Or crop down to 704 for distribution with a DAR of 4:3 (or even permanently resize down to 640x480).

[dellsam34]

I picked a video with a large circle for testing and I measured the circle in 720 mode with 4:3 aspect ratio flag and then from the master files I made a sample that I cropped to 704 with the same 4:3 flag (SAR 10/11) and the 704 sample gives a perfect circle with an almost identical H and V diameters to the mm precision on a 24" monitor so this confirms the ITU-Rec 601 (CCIR-601 or D1) standards is adopted by my capture device which is a good news, I will test with PAL files later.

Here is the 704x480 NTSC sample

[jjeff]

Interesting, Panasonic standalone DVDRs prior to '06 used 704x480 full D1 resolution and then in '06 and beyond switched to 720x480, are you saying the older Panasonics may have advantages for copying old analog material like VHS tapes? Personally I've preferred the 720 Panasonics thinking I get a tad bit better resolution but truthfully I'm not sure I've ever noticed any difference.....

[dellsam34]

720 resolution later in the digital production used the full 720 as active video pixels for anamorphic materials known as widescreen DVD's and 16/9 camcorders. It would have been better if they set the standard to 720(active video)+16 lines but they didn't so when we crop the captures to 704 we have to give each pixel an aspect ratio of 10/11, a slight horizontal squeeze to fit in the 4/3 frame which is the reverse action of what was done by the capture card, that's why the circle checked out.

Capturing analog video to DVD doesn't make sense anymore nowadays and it's a lossy process, Never done it, never will. But I guess it depends on how the DVD recorder handles the aspect ratio, You will have to ask someone who has one.

[KarMa]

My JVC DVD recorder will capture at 720x480 at the higher bitrate settings.