HDTV AVI aspect ratio

[cheerful]

I've downloaded a HDTV recording. MPC shows the following information.

Video Size: 1440 x 1080 (AR 20:11)

I know this is a recording of 1920x1080p broadcasting.

1. What does AR 20:11 mean?

2. What setting do I use to view it at 16:9?

Thanks!

[Krispy Kritter]

AR is the ratio of height to width. For example, assume this measurement is in inches. 1:1 would be 1 inch high by 1 inch wide. In your example above, it would be 20 inches by 11 inches. A typical TV is 4:3, most widescreen TV's are 16:9.

Since it isn't a 16:9 recording, you can't view it at 16:9 without distorting the picture or with black bars.

The real question is what type of display are you trying to use?

[cheerful]

on LCD screen. when I force it to 16:9, it changes a little (from 20:11).

1440:1080 is 4:3 with square pixel.

The recording resize the source from 1920x1080 to 1440x1080.

Can I edit the file to change AR to 16:9?

[edDV]

on LCD screen. when I force it to 16:9, it changes a little (from 20:11).

1440:1080 is 4:3 with square pixel.

TV recording is often done with non square pixel aspect ratio (PAR). The player sets the display aspect ratio by horizontally stretching the picture from 1440x1080 to square pixel 1920x1080.

This is the same issue as wide DVD or wide DV video stored as 720x480 but displayed as 853x480 in square pixel displays (720x576 to 1024x576 for PAL).

Some displays like many wide plasmas have 4:3 size screen pixels. In those cases 1024x768 or 1440x1080 displays as 16:9 aspect ratio.

[cheerful]

I know the source is 16:9. I think there is some mistake at the recording stage set it to 20:11. The question is: this AR must be saved somewhere in the AVI file. Is there any way for me edit it to 16:9?

[edDV]

A 16:9 1920x1080 display would show 20:11 as a slight letterbox (1920x1056 active) or as side cropped 1920x1080. Most monitors would probably lose the letterbox to overscan.

[turk690]

I don't think 20:11 is incorrect. This is the AR of the original material. Unlike standard DVD, not every HD program stream is only either 16:9 or 4:3. These are merely the most common display device visual ARs that there are. A true blue HD display device will read the tag of the stream, and vis-a-vis your display settings, repurpose it on screen by adding more or less pixels to the black bars left/right or top/bottom. Or none if you choose to zoom. The objective is to have a picture of correct proportions automatically all the time.

[cheerful]

Someone else did the recording so I am not sure what happened.

Do you mean the HDTV signal comes in at 1920x1080 with 24 lines used for letterbox? This AVI has no subtitle and is 1440x1080. In this case, I would think only the horizontal are re-sized to get to 4:3. When played back, the horizontal lines would be stretched to 1920 to get back to 16:9.

When I play with Media Player Classic and choose to force to 16:9, the screen did change a litte (the default is definitely not 4:3). So my guess is that it's 20:11.

So my question is:

1. why is it marked as 20:11? How does the player stretch it? Keep 1080 vertical lines?

2. Is it more correct to change it to 16:9?

3. How do I edit the AVI file to 16:9?

Thanks!

[jagabo]

1. why is it marked as 20:11?

If it's an MPEG4 AVI MPC reports the Display Aspect Ratio (DAR) flag (and displays using that flag). With MPEG4 video the frame dimensions are independent of the display aspect ratio. Any frame size can be used to encode any display aspect ratio.

How does the player stretch it? Keep 1080 vertical lines?

Depends on the player and how you're playing it. When windowed some will keep the height and adjust the width. Some will keep the width and adjust the height. If set to full screen, or in a resized window, both the width and height may be adjusted.

2. Is it more correct to change it to 16:9?

Not if the 20:11 is correct.

3. How do I edit the AVI file to 16:9?

If it's Divx/Xvid you can use MPEG4Modifier to change the DAR flag to whatever you want.

[Wile_E]

The source was probably recorded anamorphic(1440x1080) and then the player stretches it back to (1920x1080).
Same concept as anamorphic DVD's.

[cheerful]

If the source is 1920x1080 at 16:9, and the AVI file is 1440x1080 at 4:3, how can 20:11 be correct? I don't want to ruin the file by editing it until I understand this madness.

Thanks!

[edDV]

This ref associates 20:11 as PAR for 16:9 video for NTSC CVD (352x480) and SVCD (480x480)
http://www.mir.com/DMG/aspect.html

20:11 could also be a side cropped 2:35:1 film aspect ratio.

[jagabo]

The difference between 20/11 and 16/9 is very small. Only about 2 percent. Not worth worrying about.

MPEG4Modifier doesn't reencode. It makes a copy of the file with the PAR flags set to the new value.

[cheerful]

I know the difference is small b/w 20:11 and 16:9. However, I would really like to understand how it comes to 20:11.

The thing really confusing to me is this:

The source is 1920x1080 HDTV. The result is 1440x1080 AVI. So it seems the vertical line number is kept as it is and the horizontal lines are resized. There is no cropping during the process as the user said the AR should be 16:9. Yet it's 20:11 in the file. I don't quite understand why the letterbox comes into play when you record a TV show. If not, then there is some kind of human or software error involved to produced 20:11 instead of 16:9.

I've read the article. It has no the HDTV in it (mentioned HDTV in widescreen but example is not). I thought there would be no cropping or overscan for HDTV, right?

[jagabo]

My guess is this:

With a 720x480 DVD compatible MPEG file the 4:3 or 16:9 image appears in the inner 704x480 portion of the image. The left and right sides are padded with 8 pixels each to bring the full width up to 720.

I suspect the file you have has the 16:9 picture encoded in the inner 1408 (2 * 704) pixels and then edges of the frame are padded out to 1440 (2 * 720) pixels. Hence the full frame encodes a slightly wider than 16:9 picture, a 20:11 picture:

16 / 9 * (1440 / 1408) = 20 / 11

The proper way to display this on a 16:9 display is to crop 16 pixels off the left and right edges and display what's left as 16:9.

[cheerful]

Now that makes sense! I examine the video and there are black border on both sides. To my naked eye, it's more than 16 pixels. Maybe the broadcasting source padded it already and then it's padded again by the encoder. Maybe it's for correcting overscan for non-HD TV. Anyhow, that clarified the picture. Thanks a lot!

Then, is there a lossless way to crop an AVI with MPEG4?

[edDV]

Commercial DVD is encoded 720x480. Digital SD ATSC is broadcast 704x480. NTSC material captured to 720x480 will show a central 704x480 active picture area with 8 pixels of padding on either side.

When cable/sat/ATSC tuners downscale 1080i or 720p to S-Video NTSC and you capture that to 720x480, you get the same 704x480 active picture with 8 black pixels left and right.

What you might have is an SD or downscaled HD broadcast source that has been upscalled 2x horizontal to 1440 with 16 padding left and right.

[edDV]

For vertical, they may have upscaled 2x to 960 vertical with padding to 1080. This would appear as 60 lines ot letterbox top and bottom and a distorted horizontally squished aspect ratio.

If the 1440 is H expanded 1.3333x to 1920, the outer 1920x1080 frame would be 16:9 but the inner 1408x960 frame expanded 1.3333x horizontal is 1877x960 (1.95:1) which is a little wider than 16:9 (1/78:1) but also wider than 20:11 (1.81:1).

No cigar but getting close.

[jagabo]

Some sort of HDV camcorder is my guess.

[edDV]

Some sort of HDV camcorder is my guess.

HDV 1080i would fill the 1440x1080 frame.

[jagabo]

Some sort of HDV camcorder is my guess.

HDV 1080i would fill the 1440x1080 frame.

Even from a "broadcast" source?

[edDV]

Some sort of HDV camcorder is my guess.

HDV 1080i would fill the 1440x1080 frame.

Even from a "broadcast" source?

I'm not sure. Can any HDV camcorder record a 1920x1080i input?