Calculation of Color Rate - NTSC

[dellsam34]

I don't understand your question but computers have wider compatibility with video formats than TV's and smart devices.

[chris319]

Would these numbers apply if the video is produced for a computer screen instead of a TV?

ITU BT.601 has all the timing specs.

https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-7-201103-I!!PDF-E.pdf

[dellsam34]

That's for people who do hardware and software design, Not very useful for end users.

[chris319]

The BT.709 spec might be more useful for timing data.

https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-6-201506-I!!PDF-E.pdf

[dellsam34]

I think dellsam has a camcorder he can use to shoot some 4:3 footage of a round object for a test.

To do it right you need to measure the on-screen dimensions of a round object rather than eyeball it, so his test is potentially very useful.

Ok the results are in, See for yourselves:
I used a CD on the table and I tried to be as perpendicular as possible, I used the original Video8 format and taped it, captured the tape @ 720x480 and then cropped the frame to 704x480 and encoded with a PAR of 10:11 (DAR 3:4). I measured in my computer screen with MPC-HC set to default so it uses the pixel aspect ratio flag and the circle measured perfectly to the mm scale on 16" screen, I set MPC-HC to ignore the PAR and set it to 3:4 DAR and the circle again measured perfectly. Did the same test with 720x480 and set the PAR to 8:9 and the CD was slightly horizontally squeezed.

See the attached video file and measure for yourself.

Also here is a square crop:

[jagabo]

Yes, that's a test that didn't need to be done. Anyone who's done video capture in the last 10 years knows that almost all capture devices conform to the ITU spec.

[dellsam34]

Unfortunately a lot of people need to see it. If everyone knows everything a forum like this wouldn't have existed.

[GrouseHiker]

Unfortunately a lot of people need to see it. If everyone knows everything a forum like this wouldn't have existed.

I appreciate this test, since I'm still trying to sort this out.

So a PAR of 10:11, displayed on a square-pixel monitor (set to native resolution) displays proper proportions?

[GrouseHiker]

Yes, that's a test that didn't need to be done. Anyone who's done video capture in the last 10 years knows that almost all capture devices conform to the ITU spec.

Is the ITU spec you reference H.264?

[chris319]

How was the PAR of 10:11 arrived at?

[jagabo]

It's simple algebra:

DAR = FAR * SAR

DAR = display aspect ratio (final width:height of displayed image)
FAR = frame aspect ratio (framewidth:frameheight)
SAR = sampling aspect ratio, sometimes called PAR, pixel aspect ratio

4:3 = 704:480 * SAR
4/3 = 704/480 * SAR
4/3*480/704 = SAR
10/11 = SAR
10:11 = SAR

[GrouseHiker]

It's simple algebra:

DAR = FAR * SAR

DAR = display aspect ratio (final width:height of displayed image)
FAR = frame aspect ratio (framewidth:frameheight)
SAR = sampling aspect ratio, sometimes called PAR, pixel aspect ratio

4:3 = 704:480 * SAR
4/3 = 704/480 * SAR
4/3*480/704 = SAR
10/11 = SAR
10:11 = SAR

What took me a little while to grasp was cropping actually changes SAR. Therefore, cropping also changes PAR, since DAR always remains constant - correct?

[jagabo]

Cropping does not change the sampling aspect ratio. If you trim away the edge of a sheet of graph paper the shape of the remaining grid is unchanged.

[chris319]

Nice job, dellsam, thank you.

I found the test interesting even though I'm not planning to capture hi 8 tape.

As the video shows, there are pillars on the sides which is to be expected when fitting a 4:3 image into a 16:9 frame.

Is the ITU spec you reference H.264?

No, H.264 is a compression scheme.

If you're interested in standards:

SMPTE 259M-A supports 768 x 525 (1.59 : 1)

SMPTE 259M-C supports 720 x 525 (1.49 : 1)

SMPTE 259M-D supports 960 x 525 (1.99 : 1)

The 525 figure equals 483 visible scan lines + 42 lines of vertical blanking (both fields).

16 / 9 * 483 = 858

4 / 3 * 483 = 644

[dellsam34]

I found the test interesting even though I'm not planning to capture hi 8 tape.

It has nothing to do with Hi-8 tapes, Every analog video format from 2" quad to Betacam SP including the consumer format Betamax/VHS/8mm should be captured the same way.

How was the PAR of 10:11 arrived at?

You only have to worry about PAR (Pixel Aspect Ratio) and DAR (Display Aspect Ratio), SAR (Storage Aspect Ratio) is a theoretical aspect ratio of a said resolution if the pixels were square: for example SAR = 704/480 and it is considered a PAR by most modern software.

DAR = SAR x PAR
4/3 = 704/480 x PAR
PAR = 4/3 x 480/704 = 1920/2112 = 10/11 NTSC
PAR = 4/3 x 576/704 = 2304/2112 = 12/11 PAL/SECAM

If you're interested in standards:

SMPTE 259M-A supports 768 x 525 (1.59 : 1)

SMPTE 259-M-C supports 720 x 525 (1.49 : 1)

SMPTE 259M-D supports 960 x 525 (1.99 : 1)

The 525 figure equals 483 visible scan lines + 42 lines of vertical blanking (both fields).

16 / 9 * 483 = 858

4 / 3 * 483 = 644

Those are SMPTE 259 digital format (Betacam digital formats and the likes) they are not ITU D1 specs.

[jagabo]

Be careful about the acronyms being used. Dellsam34 and I are using the same acronyms for different things. In my equation in post #41 SAR (sampling aspect ratio) is the same thing as PAR (pixel aspect ratio) in his equation. My FAR (frame aspect ratio) is the same thing is his SAR (storage aspect ratio).

Also note the Sample Aspect Ratio (Pixel Aspect Ratio) numbers are approximations.

https://web.archive.org/web/20160606132336/https://www.doom9.org/showthread.php?p=1058927

Beyond that there is the issue of aspect ratios on DVDs. The DVD spec refers to the MPEG 2 spec for aspect ratio information. The MPEG 2 spec uses a 4 bit number to indicate the aspect ratio. Of the 16 possible values only 4 are defined:

value  meaning
1      1:1 Sample Aspect Ratio
2      4:3 Display Aspect Ratio
3      16:9 Display Aspect Ratio
4      2.21:1 Display Aspect Ratio

The other 12 values are forbidden or reserved. Of those 4 possible values only two are allowed on DVD 4:3 and 16:9 Display Aspect Ratio.

The MPEG 2 spec also indicates the Display Aspect Ratio is comprised of the entire frame, not a 704x480 portion of a 720x480 frame. But most DVDs made from ITU rec.601 720x480 caps are not corrected for this. They just convert to 720x480 MPEG and mark it 4:3 DAR. The DVD and BD players I've tested are schizophrenic about this. They follow the ITU spec at the composite output, the DVD spec at the upscaled HDMI output.

[GrouseHiker]

Cropping does not change the sampling aspect ratio. If you trim away the edge of a sheet of graph paper the shape of the remaining grid is unchanged.

Be careful about the acronyms being used. Dellsam34 and I are using the same acronyms for different things. In my equation in post #41 SAR (sampling aspect ratio) is the same thing as PAR (pixel aspect ratio) in his equation. My FAR (frame aspect ratio) is the same thing is his SAR (storage aspect ratio).

What I was trying to say:

Cropping changes the "Storage Aspect Ratio" and the "Pixel Aspect Ratio," since "Display Aspect Ratio" is a constant until the video is resized. Is this true?

For example, sampling a 640 x 480 (4:3) Display Aspect Ratio at 720 x 480 (3:2) produces a Pixel Aspect Ratio of 8:9 (I know this includes blanking).

Cropping this capture to 704 x 480 produces a new Storage Aspect Ratio (22:15) and a new Pixel Aspect Ratio of 10:11.

Throughout this process, the Display Aspect Ratio remains 4:3.

Is this correct?

[jagabo]

Cropping does not change the sampling aspect ratio. If you trim away the edge of a sheet of graph paper the shape of the remaining grid is unchanged.

Be careful about the acronyms being used. Dellsam34 and I are using the same acronyms for different things. In my equation in post #41 SAR (sampling aspect ratio) is the same thing as PAR (pixel aspect ratio) in his equation. My FAR (frame aspect ratio) is the same thing is his SAR (storage aspect ratio).

What I was trying to say:

Cropping changes the "Storage Aspect Ratio" and the "Pixel Aspect Ratio," since "Display Aspect Ratio" is a constant until the video is resized. Is this true?

Oh, sorry, I misunderstood (hence the previous post!).

It depends on whether the final video is flagged with a Display Aspect Ratio or Pixel Aspect Ratio. If it's flagged with a DAR the PAR changes. If it's flagged with a PAR the DAR changes.

In other words, when flagged with a DAR you're saying display this picture with this DAR regardless of the frame size. When you specify the PAR you're telling the player to calculate the DAR based on the frame size and the PAR.

[GrouseHiker]

It depends on whether the final video is flagged with a Display Aspect Ratio or Pixel Aspect Ratio. If it's flagged with a DAR the PAR changes. If it's flagged with a PAR the DAR changes.

In other words, when flagged with a DAR you're saying display this picture with this DAR regardless of the frame size. When you specify the PAR you're telling the player to calculate the DAR based on the frame size and the PAR.

Is the video "flagged" DAR or PAR during processing with Avisynth? Is there a default flag?

[dellsam34]

Cropping changes the "Storage Aspect Ratio" and the "Pixel Aspect Ratio," since "Display Aspect Ratio" is a constant until the video is resized. Is this true?

For example, sampling a 640 x 480 (4:3) Display Aspect Ratio at 720 x 480 (3:2) produces a Pixel Aspect Ratio of 8:9 (I know this includes blanking).

Cropping this capture to 704 x 480 produces a new Storage Aspect Ratio (22:15) and a new Pixel Aspect Ratio of 10:11.

Throughout this process, the Display Aspect Ratio remains 4:3.

Is this correct?

Again don't worry about the SAR, it may have weird numbers but those are just theoretical numbers to define the pixel count ratio between the H and V, What is important for getting a correct frame displayed is the PixelAR and DisplayAR.
The PAR is the same for both 704 and 720 but the advantage of using 704 over 720 is that the DAR is a perfect 4/3 for the whole frame for 704 but it is not a perfect 4/3 for 720, This is not an issue for widescreen displays but for 4/3 displays the 720 will have to be slightly squeezed horizontally. In addition some software and hardware are designed to display 720 in widescreen thinking it's a WS DVD spec, that's why you see a lot of captures on youtube videos shown as widescreen while they are not. The last advantage is you don't have to see those ugly grayish bands on the screen as demonstrated in the above clip.

[poisondeathray]

It depends on whether the final video is flagged with a Display Aspect Ratio or Pixel Aspect Ratio. If it's flagged with a DAR the PAR changes. If it's flagged with a PAR the DAR changes.

In other words, when flagged with a DAR you're saying display this picture with this DAR regardless of the frame size. When you specify the PAR you're telling the player to calculate the DAR based on the frame size and the PAR.

Is the video "flagged" DAR or PAR during processing with Avisynth? Is there a default flag?

Avisynth assumes square pixel

It depends on the format you are using (eg. MPEG2, AVC , HEVC, etc..) , but it's done usually during encoding, at the video stream level. Sometimes the container can contain aspect ratio information as well (e.g. MKV can)

[dellsam34]

Is the video "flagged" DAR or PAR during processing with Avisynth? Is there a default flag?

NTSC:

ffmpeg -i In.avi -vf "format=yuv420p,setsar=sar=10/11" -c:v libx264 -crf 10 -x264opts colorprim=smpte170m:transfer=smpte170m:colormatrix=smpte170m:force-cfr -c:a aac -b:a 192k Out.mp4

PAL:

ffmpeg -i in.avi -vf "format=yuv420p,setsar=sar=12/11" -c:v libx264 -crf 10 -x264opts colorprim=smpte170m:transfer=bt470bg:colormatrix=bt470bg:force-cfr -c:a aac -b:a 192k Out.mp4

SetSAR just means set PAR I believe. These are poisondeathray commends.

[jagabo]

Is the video "flagged" DAR or PAR during processing with Avisynth? Is there a default flag?

No, during encoding (stream level) or muxing (container level).

[Cornucopia]

Here we go again...

There is no real thing "storage aspect ratio". That is just a shortcut for H & V that non-pros have gotten use to using to cut corners, and it's come back over and over to bite people on the a$$. As seems to have happened here.
And I would venture to bet that the term NEVER appears in any professional, official engineering document either.

Display AR = Horizontal / Vertical * Pixel AR

Scott

[dellsam34]

Yep, Since the start of digital and over the years not only several names used but we've seen real consequences of lack of knowledge or careless even in the pro world such as TV channels, stretched frames, letterboxed on all sides, squeezed vertically with black bars on top and bottom....etc, Add to that the lack of knowledge of the consumer who bought those fancy TV sets but don't know how to use them. And if we talk about youtube, God help us, I literally argued with someone who posted a capture on youtube that is horribly stretched to fill 16/9 frame and he was so confident that it should look that way.

[jagabo]

There is no real thing "storage aspect ratio".

There is if you define it. These are all symbolic notations.

[GrouseHiker]

I know I'm going to catch some heat for this, but I can handle it...

I just like being able to understand the numbers. I'm sure some of the capture resolutions are way out there. I researched blanking timing of the active picture, but couldn't find it... just backed in to the 1.1 microseconds.

The black numbers are calculated in Excel.


[Attachment 53542 - Click to enlarge]

[GrouseHiker]

Is the video "flagged" DAR or PAR during processing with Avisynth? Is there a default flag?

NTSC:

ffmpeg -i In.avi -vf "format=yuv420p,setsar=sar=10/11" -c:v libx264 -crf 10 -x264opts colorprim=smpte170m:transfer=smpte170m:colormatrix=smpte170m:force-cfr -c:a aac -b:a 192k Out.mp4

SetSAR just means set PAR I believe. These are poisondeathray commends.

So in ffmpeg, "setsar" sets Pixel Aspect Ratio. In your example, it's set to 10/11. https://ffmpeg.org/ffmpeg-filters.html#setdar_002c-setsar


So this ffmpeg filter sets a flag so that the player will display properly - whatever the Pixel Aspect Ratio may be? Bottom line, I can set this flag and I don't have to resize to 640x480 to get proper portions?

Does this approach work on all players: Apple, PC, Smartphone, YouTube?

[chris319]

I see you are using the rs170m color space. Have you taken into account that your Hi-8 original is interlaced?

[dellsam34]

I de-interlace first before encoding, As far as setSAR to 10/11, I've tried it on few software players, my iPhone and LG TV and so far the 4:3 DAR is produced perfectly.