Video aspect ratio conversion

[cd090580]

Hi,

I have a divx file with a resolution of 640*352 (so about 1.85:1 ratio).
This file is 23.976 fps.

I am converting it to a pal dvd. But i have a problem for keeping the right aspect ratio. I want to encode it as 16:9 dvd anamorphic.

Here is the avisynth script generated by fitcd.

LanczosResize(704,560,0,1,640,350)
AddBorders(8,8,8,8)
AssumeFPS(25.000, true)

What I think strange is that there is no black bars at all. A true 16/9 is about 1.77:1 ratio but my movie is 1.85:1. So I think the horizontal bars are not correct. What are the right values ?

Source: 640x352 23.976 fps progressive
Target: PAL DVD 720*576 25 fps anamorphic.

I encode with CCE. SO what are the settings for the encoder too. It's the first time I encode to anamorphic.

[manono]

What I think strange is that there is no black bars at all

What do you think the AddBorders(8,8,8,8) does? It puts an 8 pixel border all the way around the video. Open the script in VDub(Mod) and you'll see the black. I'm assuming you're using a 1 block overscan on purpose.

A true 16/9 is about 1.77:1 ratio but my movie is 1.85:1.

It's closer to 1.82:1.

[cd090580]

Ok, So it's correct with that 8 pixels black bars added in top and bottom ?????

[jagabo]

LanczosResize(704,560,0,1,640,350)

If your source is YV12 you're blurring the chroma channels by doing this. Keep your crops on mod2 boundaries to avoid it.

[cd090580]

ok,

so could you give me the script with the right values for addborders and lanczosresize ?

Thanks a lot

[manono]

If you don't need the 1 block overscan, then:

LanczosResize(720,576)

or:

LanczosResize(720,560)
AddBorders(0,8,0,8)

Take your pick. The second one is based more on ITU resizing and has the black bars above and below you were asking about. If you really did want the 1 block overscan (why?), then:

LanczosResize(704,560)
AddBorders(8,8,8,8)

[guns1inger]

If you really did want the 1 block overscan (why?) . . . . . . .

I can think of two reasons

1. Hardcoded subtitles that have been poorly placed and would fall into a standard overscan black hole

2. I often used to add 1 - 2 blocks of overscan to reduce the actual amount the image had to be resized up. As these areas weren't going to be seen anyway, anything that helped improve image quality during processing was worth trying.

[manono]

As these areas weren't going to be seen anyway, anything that helped improve image quality during processing was worth trying.

Very true. I keep forgetting that I don't reencode AVIs (but watch them as-is on my player), and only reencode DVDs. In addition, as near as I can tell my TV doesn't overscan.

But we don't know for sure that's the case with cd090580, who may have left it at 1-block overscan from a previous encode or from just playing around, and may not be aware of the fact. Or not.

[guns1inger]

My old TV used to overscan approx 4% top and bottom, and around 3% on one side, and 5% on the other (i.e. not centred). I haven't looked at the overscan on the LCD TV yet.

[minidv2dvd]

overscan is an old tube tv trick to make them last longer. as the magnets in tube tvs age they weaken and the picture will shrink, so manufacturers used overscan to make the picture fill the whole screen for a longer period of time.

newer type lcd and plasma tv formats have no overscan area as the picture area doesn't shrink over time.

[jagabo]

newer type lcd and plasma tv formats have no overscan area

Yes, they do. Some have non-overscan modes but usually the default is to overscan. They continue to do this because there is often junk at the edges of the frame -- left there by broadcasters, cable/sat retransmissions, cable/sat boxes, etc.

[manono]

Could it be that some of these new sets overscan broadcasts and not DVDs? I don't have any special non-overscan mode that I can find in my Sony LCD, but when watching DVDs it doesn't seem to overscan, not on the top and bottom anyway. I'm not positive about the sides. How do I know this? Say I'm filtering with a bobber and repal or a bobber and mrestore to remove blends. You know how sometimes you'll get that 1 pixel of "flickering" at the top and/or bottom after a bob. Sometimes I forget to mask it out or crop it away and resize, and I can see it clearly doing that flicker thing when watching the finished DVD on the TV set.

[jagabo]

Make yourself a DVD with an overscan test pattern:



Actually, that pattern may not work well because the overscan is typically more than 20 pixels.

[manono]

I apologize for being late with my reply. I was busy for awhile, then I forgot for awhile, and then I was busy again. Anyway, I finally burned it as a 16:9 DVD and had a look. The pic was taken with my wife's cell phone camera of the DVD being played on the TV set. I apologize for the crummy pic, but didn't realize until later that the camera was moving as I took the picture. I don't guess you have any trouble seeing there's no overscan.



Costco and Sam's Club call the TV the Sony Bravia KDL-46VL130. At most other places it's called the Sony Bravia KDL-46V3000. The DVD player is an Oppo DV-981HD feeding the TV set over an HDMI cable. My guess is that no overscan is common when viewing DVDs over HDMI to LCD sets. One factor often neglected is the fact that the majority of DVD players crop some pixels before sending the picture to the TV set. Some of the lost picture that gets blamed on the overscan might not be because of overscan at all.

In case others might want to find out how much, if any, their overscan is, I've prepared 2 DVDs, one for 4:3 video and the other for 16:9 video, each 30 seconds long. Zipped up they're each 52 KB. Unzipped they're each just under a MB. Unzip them and you'll find the IFOs, BUPs, and VOB in the VIDEO_TS folder, along with the AUDIO_TS folder, ready to burn using ImgBurn to a DVD-RW (or a CD, if your player can play Mini-DVDs).

crop_test_16_9.zip

crop_test_4_3.zip

[cd090580]

Thanks a lot for your test patterns but I noticed it's an NTSC dvd, will it work for a PAL tv and dvd player ????????

[manono]

I apologize, cd090580. I completely forgot about the majority of the world that's PAL. I think all it will show in PAL players is the amount of overscan when playing an NTSC DVD. Better would be to test using a PAL DVD.

I'll be back with a couple of those...

pal_overscan_test_4_3.zip

pal_overscan_test_16_9.zip

Even though the pic itself still says 720x480, I resized it to 720x576 before making the 2 PAL DVDs. I just tried the PAL 16:9 one in my own player and it still shows no overscan. Maybe PAL people playing both the NTSC version and the PAL version will have the same amount of overscan, I don't know. And as jagabo mentioned earlier, the 20 pixel max that the picture shows may not be enough for a lot of people, especially those using composite cables to connect their player to a CRT television set.

Also, if you play just the 16:9 DVD VOBs, they'll play as 4:3. That's because I used the same VOBs for both the 4:3 and 16:9 DVDs, but changed the DAR for the 16:9 DVDs in the IFOs. Played as DVDs they should play as 16:9. Most (but apparently not all) DVD players get the DAR information from the IFOs and not the VOBs themselves.