AVI Aspect Ratio

[SEALs1230]

I'm not sure if this is the right place to post this...I have avi files that are pretty widescreen, what I mean is that the black borders are huge. If you buy a widescreen DVD and compare it to the avi file the professional DVD you bought would have borders about half as large as the ones on all my avi files. I want to encode these avi files using TMPGEnc and then author them with TMPGEnc DVD Author and burn with Nero. They all have ac3 audio that I have to extract prior to encoding. Is there a way to take these files and edit them in such a way that I can still have widescreen but with smaller borders? Before I started using TMPGEnc, I used DivXtoDVD and it would take care of the border problem automatically. So I'm pretty sure it can be done, I'm just not sure what guides and tools to use. Thanks.

[guns1inger]

What is the actual resolution, so we know the actual aspect ratio. If they are letterboxed 4:3 you are better off encoding them as is, and zooming with your player or TV.

If you feel the need to crop and resize, you could look at this post https://www.videohelp.com/forum/viewtopic.php?t=259618

or this one

https://www.videohelp.com/forum/viewtopic.php?t=259356

or this one

https://www.videohelp.com/forum/viewtopic.php?t=258721

[SEALs1230]

I put it through G-Spot and it said the resolution was "640x272 (2.35:1) [=40:17]" what I would like to do (if possible) is get it into a 16:9 widescreen format. I tried cropping it like the guy told me to do in the first forum post that you linked, but that just made the video have borders on all sides rather than getting ride of the borders on the top. Any suggestions?

[guns1inger]

You are always going to get borders top and bottom unless you cut the ends off. 2.35 is a very narrow format, so the borders will take up more than a third of the screen. If you read my post from the third reference, I gave the following calculations and virtualdub instructions, which work for me :

"Use the builtin resize filter. In the top section set the new resolution to the resolution of the PICTURE. Choose Lanczos3 as the resize filter.

Tick the box marked Expand frame and letterbox image and set these to be the full frame resolution (NTSC 720 x 480, PAL 720 x 576).

When calculating for NTSC, I use the following.

Divide 720 x the horizontal resolution of the clip
Multiply the results of that by the vertical resolution to get the new vertical res. Multiply that by 0.9090 to compensate for pixel resolution.

eg. Original is 608 x 256

720/608 = 1.18421
1.18421 x 256 = 303
303 x 0.9090 = 275.4 (round to 275)

therefore new resolution is 720 x 275

This will look wrong in the output window of Virtualdub if it is still set to Free Adjust or 1:1. Set it to 4:3 to see it correctly. "

I worked this out pretty much by myself, so it's not that hard.

[SEALs1230]

"Use the builtin resize filter. In the top section set the new resolution to the resolution of the PICTURE. Choose Lanczos3 as the resize filter.

When calculating for NTSC, I use the following.

Divide 720 x the horizontal resolution of the clip
Multiply the results of that by the vertical resolution to get the new vertical res. Multiply that by 0.9090 to compensate for pixel resolution.

eg. Original is 608 x 256

720/608 = 1.18421
1.18421 x 256 = 303
303 x 0.9090 = 275.4 (round to 275)

therefore new resolution is 720 x 275

This will look wrong in the output window of Virtualdub if it is still set to Free Adjust or 1:1. Set it to 4:3 to see it correctly. "
.

The PICTURE, is that the source avi file? The calculated number, do I have to do anything with that? or is that just sort of for my information. Also, I'm trying to get the 16:9 widescreen for my computer so how come I set it to 4:3, or do I have to do that regardless?

[guns1inger]

Yes, the picture resolution is the movie resolution. The cilculated number is the new vertical resolution, so yes, you need it. This calculation is for 4:3. Unless you original avi is anamorphic, there is nothing to be gained from going to 16:9 when most players and WS TVs can zoom al letterbox image correctly.

However, if you want to try it, use 1.2121 in the calculation, in place of 0.9090

If you are in PAL land, use 0.9074074 for 4:3, and 1.45679 for 16:9

[SEALs1230]

Sorry I'm being so thick but before you said to put into the new resolution, the resolution of the source. Well if i'm doing that, how can I enter the calculated resolution as the new one. I think I'm just understanding this wrong. I'm sorry

[guns1inger]

OK, lets take your clip as an example. I am assuming NTSC here.

Your movie currently has an aspect ratio of 640 x 272. You want to get a 16:9 clip out at the end.

Target horizontal resolution is 720, so 1:1 increase will be 720/640, or 1.125

Multiply your current vertical resolution by this number to get you target resolution (1:1). So, we go 272 x 1.125, which gives us 306. Now, this assumes 1:1, or square pixels, which TV is not. For 16:9, we need to add a stretch factor to counter this. For NTSC, that factor is 1.2121. So, 306 x 1.2121, which gives us 370.92. I'd round this up to 371 to be safe.

So, we have now gone from a source AR of 640 x 272 with a 1:1 pixel aspect ratio, to a 16:9 NTSC target resolution of 720 x 371.

Ah ha, I hear you cry, 371 is not a valid resolution. You're right. We need to pad this out to 480 before we can encode. If you use VirtualDub and the built in resize filter, this is simple. Put the caluclated sizes into the top (720 and 371), choose your filter (I use Lanczos3 most of the time), then tick the box marked expand frame. In the new fields that have opened up, put in 720 and 480. This will add the missing black bars required even for 16:9 material.

Now if you preview, the image should look messy until you switch your preview window to 16:9 to see it correctly. If you required PAL output, use the factors from my previous post.

One final thing. Most avi files are 1:1. When you resize, you will generally soften the image. When you resize to 16:9, you will soften if further. I'd suggest looking at at least one further filter. I use the Unsharp mask filter by Antonio Foranna and Donald Sharp, with a diameter setting of 3 (5 in a few cases). This will address the softening. You may also need the MSU block filter for some source material to address compression artifacts after the resize.

[SEALs1230]

Is the unsharp mask filter the same one as the sharpen filter?? And thanks for that last post. I understand it well now. I dunno why I was having such a hard time...sorry about that.

[guns1inger]

It uses a different algorythm, and doesn't come as part of the standard download.

I am currently writing (my first piece of code in about 10 years) a calculator to do this. I'll make it available to all once it's done.

/edit Sometime later than day . . . .
OK. If you feel brave and want to have a play, here it is.
http://users.tpg.com.au/adslrotx/Apps/aviresizecalc.zip

I take no responsibility if it eats your machine, sleeps with your partner or gives you incorrect information. Given that it has been less than 3 hours since inception, testing has been minimal, as is the error checking.

Please feel free to comment or PM me if you want.

/end edit