4:3 video in 16:9 frame

[VideoFanatic]

I have a 720 x 576 video. It's a 4:3 video with side borders encoded to a 16:9 aspect ratio. I need to crop borders

I'm not sure if the original dimensions without the borders were 544 x 576 or 540 x 576. How can I find out? I need to know because I'm cropping 8 pixels of junk off the top and bottom so how do I know the correct width to crop to maintain the correct proportions. At the end I'm resizing to 720 x 576. This is my script. I'm cropping all the side borders and junk pixels in the width.

Crop(96,4,-104,-4)
QTGMC(Preset="Slower")
AddBorders(90,0,90,0, $000000)
Spline36Resize(720,576)

[PuzZLeR]

There are several solutions to this, but as a start, using the following equation will never fail you or distort your video:

Width/Height = DAR/PAR

DAR = Display Aspect Ratio
PAR = Pixel Aspect Ratio

Let us know if you're still stuck.

[VideoFanatic]

Sample is in my 1st post. DAR is 720 x 576. What is the PAR?

[Skiller]

I'm not sure if the original dimensions without the borders were 544 x 576 or 540 x 576. How can I find out?

720 / ((16/9) / (4/3)) = 540

544 is a broadcast resolution (544x576) and it is always padded from 540 (so it's mod16 for MPEG2 encoding), but this is not related to pillarboxing (4:3 in 16:9 frame), albeit it results in exactly the same loss of horizontal resolution (25% of horizontal resolution are lost due to the pillarboxing).

I need to know because I'm cropping 8 pixels of junk off the top and bottom so how do I know the correct width to crop to maintain the correct proportions. At the end I'm resizing to 720 x 576.

As a side note, those 540 pixels contain what would normally stretched over an entire 720 frame in a non-pillarboxed scenario. Since this is an old video it almost certainly follows ITU scaling, meaning the 4:3 picture is covered in 704x576 and the rest is padding. This means the 4:3 area is now covered in 528x576 pixels.


Personally I wouldn't bother cropping those 8 lines and resize back to 576 but if you want to crop 4 lines at the top and bottom (8 in total) this would be the math:


(576 - 8) * (540/576) = 532.5

Crop to 532.5 x 568 and resize to 720x576


Here's another approach, it's actually the same thing.

(576 - 8) * (528/576) = 520.7

Crop to 520.7 x 568 and resize to 704x576, and optionally padd to 720.

[PuzZLeR]

Edited my post as I see Skiller pretty much covered it.

But to answer your earlier question:

Sample is in my 1st post. DAR is 720 x 576. What is the PAR?

Not quite.

Width = 720
Height = 576
DAR = 16/9 (for 16:9)
PAR = currently unknown

Plugging in the values to the mentioned equation:

720/576 = (16/9)/PAR

And doing some algebra:

PAR=1.4222222... (the 2s are recurring). This just so happens to be 64/45, which is PAL's widescreen DAR=64:45.

[LMotlow]

Cool. But the image in that video should play at 4:3. it's not a 16:9 image. It's from a 16:9 PVR capture from a telecined cable broadcast, field blended and resized. Deinterlace or Bob that clip and you'll see it's field-blend progressive video encoded as interlaced.

The creativity never ends, does it?

[VideoFanatic]

Cool. But the image in that video should play at 4:3. it's not a 16:9 image. It's from a 16:9 PVR capture from a telecined cable broadcast, field blended and resized. Deinterlace or Bob that clip and you'll see it's field-blend progressive video encoded as interlaced.

The creativity never ends, does it?

Actually it IS a 16:9 video. The broadcaster has obviously lowered the resolution of the width to 544 then added side borders to get a 720 pixel width. That way they can broadcast in 16:9. Also the video is exactly as broadcast on satellite, not cable. I didn't capture it.

[johnmeyer]

Sample is in my 1st post. DAR is 720 x 576. What is the PAR?

The PAR is 1.4568, PAL widescreen. As already pointed out, even though it is encoded as interlaced, there is no temporal difference between even and odd fields, so the video should be treated as progressive. I did not see the field blending, but there is so little motion in this clip that my poor eyes may have missed it.

[LMotlow]

Cool. But the image in that video should play at 4:3. it's not a 16:9 image. It's from a 16:9 PVR capture from a telecined cable broadcast, field blended and resized. Deinterlace or Bob that clip and you'll see it's field-blend progressive video encoded as interlaced.

The creativity never ends, does it?

Actually it IS a 16:9 video. The broadcaster has obviously lowered the resolution of the width to 544 then added side borders to get a 720 pixel width. That way they can broadcast in 16:9. Also the video is exactly as broadcast on satellite, not cable. I didn't capture it.

The image content in that video is 4:3. Period. It's a 4:3 piece of film inserted into a 16:9 broadcast with black added by the producer to fill the frame, yes. What did you think I meant? The owner can crop and stretch the damn thing if you want, and be as silly as the guy who made the clip. Suit yourself.

It's field-blended progressive. Bob the video and check the hand motions frame by frame. Most experienced members here do that sort of thing routinely.

[PuzZLeR]

Sample is in my 1st post. DAR is 720 x 576. What is the PAR?

The PAR is 1.4568, PAL widescreen. As already pointed out

Where did you get this number? Are you pointing out the widescreen DAR of the cropped 704 version of PAL, which is almost that number at DAR=16:11=1.4545 (endless 45s)? The actual video sample itself however, letterboxing and all, is DAR=64:45=1.422 (endless 2s).

[johnmeyer]

It is what Vegas Pro (my NLE) reports. I copy/pasted into my post. However, various people have taken issue with how Vegas calculates PAR. For instance, it shows a PAR for NTSC 4:3 DV video of 0.9091.

I've never gotten too hung up on this. As long as I end up with no borders, I figure I've done the math correctly. FWIW, this Wikipedia entry shows the PAL 4:3 PAR as 1.456790123:

Pixel aspect ratios of common video formats

[PuzZLeR]

It is what Vegas Pro (my NLE) reports. I copy/pasted into my post. However, various people have taken issue with how Vegas calculates PAR. For instance, it shows a PAR for NTSC 4:3 DV video of 0.9091.

I've never gotten too hung up on this. As long as I end up with no borders, I figure I've done the math correctly. FWIW, this Wikipedia entry shows the PAL 4:3 PAR as 1.456790123:

Pixel aspect ratios of common video formats

There goes Vegas again - going on auto-pilot and spitting out not only bad video, but wrong reports according to what I see.

The video sample is indeed PAR=64:45=1.42 (2 bar). And at 720x480 16:9 PAL it would need this value to avoid distortion. The value Vegas reports would be more accurate for the cropped version of PAL at 704x576 16:9, be it PAR=16:11=1.45 (45 bar) (or rounding value of 1.456790123 for Rec.601).

As per the value of PAR=0.9091, this should be for NTSC video that is cropped at 704x480 4:3 (which is actually 10:11=0.90 (90 bar), close enough). Vegas is wrong (again) if it reports this PAR value for 720x480 4:3, which should be truly 8:9=0.88 (8 bar).

All this is assuming no distortion, of course, with the source.

Again, small differences, and wouldn't distort the image noticeably. I'd only be concerned if such differences weren't compatible with a picky spec, like DvD, or blu-ray, video can be. Then again, blu-ray has the PAR messed up with SD video too.

[Skiller]

Vegas is wrong (again) if it reports this PAR value for 720x480 4:3, which should be truly 8:9=0.88 (8 bar).

It's not "wrong" per se, but Vegas (and I) believe in the ITU Rec.601 spec, whereas you seem to believe in the MPEG spec. That's the difference.
I would scale 4:3 NTSC with a PAR of 10/11, regardless of whether the frame is 720 or 704 pixels wide.

That means a frame of 720 pixels in width is always wider than 4:3 or anamorphic 16:9, because the inner 704 pixels would be exactly that (704 is cropped from 720, not resized). Yes, the MPEG spec says otherwise but tell that to any DAC or ADC.

Anyways, this has been discussed to death over the last 15 years or so and some people stick to one and some to the other and most probably don't know or care about the 2.5% difference.

[johnmeyer]

Vegas is wrong (again) if it reports this PAR value for 720x480 4:3, which should be truly 8:9=0.88 (8 bar).

It's not "wrong" per se, but Vegas (and I) believe in the ITU Rec.601 spec, whereas you seem to believe in the MPEG spec. That's the difference ... Anyways, this has been discussed to death over the last 15 years or so and some people stick to one and some to the other and most probably don't know or care about the 2.5% difference.

Yup.

Every NLE has its quirks, but this one is -- literally -- a roundoff error, hardly worth mentioning.

[PuzZLeR]

Any difference between PAR 8:9 or PAR 10:11 is indeed minor, and the distortion is not very noticeable.

But not to churn a debate or flamewar, the distortion is still there for the picky. But most of all, if encoding for a particular spec, the difference is even more important.

For example, blur-ray SD H.264 only accepts PAR=10:11 for 720x480 4:3. If the source you wish to encode is MPEG video, 720x480 4:3, with PAR=8:9, to comply with SD blu-ray H.264 you have to encode with PAR=10:11, and deal with the distortion. If you ignore this tiny detail in PAR it will not be blu-ray compliant. (It may still play, however, it will not have any guarantee.)

And to deal with the distortion, from MPEG 8:9 to 10:11, I just prefer to pad 8 pixels each side instead of stretch it. But that's me.

My point is that, when dealing with MPEG, as was this sample here, I still find it important to notice.