Seeking To Understand Aspect Ratios & XVid Encoding,

[Tom Saurus]

I am new to encoding XVid files from my existing mpeg2 files. Here is a link to a topic I launched yesterday.

https://forum.videohelp.com/viewtopic.php?t=318776

What I am trying to understand is for me other than the original mpeg2 file the XVid file that avi.net exported which was 640x432 looks much better than the one that Womble exported at a dimension of 720x480. The Womble file looks like a wide screen file and I don't have a wide screen television. What seems to have happened was the picture was stretched out by womble and the black bars on top and bottom take up more of the tv screen. I am curious as to why this happened.

Here are some sample pictures:

Picture 01, is from a mpeg2 files recorded at 720x480. It is a British Comedy Show, and there is a slight black bar at the top and bottom of the picture.

[Tom Saurus]

Here is the picture that I got from avi.net and the dimensions are 640x432:

[Tom Saurus]

Here is the normal mpeg2 file at 720x40 of the second episode of this show.

[Tom Saurus]

Here is what Womble exported as a XVid avi:

[Tom Saurus]

I record interlaced and I remember FulciLives writing that the Divx or XVid files from such a file wouldn't look all that good in a topic I read not too long ago at Videohelp. I was pleasantly surprised at how nice the picture looked when I converted it. I can't remember the name of the thread but there was part of it where they were discussing progressive vs interlaced files.

Since I don't have a widescreen tv and I don't mind the traditional ratio of the picture on the screen, can some one explain to me what happened with what Womble exported. It would seem to me that if the original dimensions of the mpeg2 file were 720x480 and I chose 720x480 as the dimensions of the XVid avi, shouldn't they look the same? Thanks in advance for any information you can give me on this subject.

[guns1inger]

What you are forgetting is that the original mpeg-2 files do not have a 1:1 Pixel Aspect Ratio (PAR) - that is, the pixels are not square. NTSC 4:3 has a different PAR to NTSC 16:9, which is different to PAL 4:3, which is different to PAL 16:9.

NTSC 4:3 is the same as 640 x 480 when adjusted for 1:1 PAR.

So when avi.net or autoGK crop off the letterbox bars and resize, they adjust for a 1:1 PAR output. You have not been making the same adjustments when doing this manually.

Edit : Using the still (above) as a sample, I opened it in Virtualdubmpeg2, and added a null transform filter. I then cropped the image 24 lines from the top and 30 from the bottom, giving me 720 x 426. I then added a resize filter and resize to 640 x 426, and got the following :

[FulciLives]

Either Womble doesn't do something it needs to do or it has options that you did not set up correctly.

I don't have the version of Womble that you have (mine is just the editor aka MPEG2VCR). So I don't know what settings there are etc. in your version.

Pretty much everyone agrees that autoGK and/or avi.net are the two best MPEG-4 (XviD/DivX) encoding programs. I suggest you forget about using Womble for creating MPEG-4 content. You can still use if for editing MPEG-2 files prior to using autoGK or avi.net

- John "FulciLives" Coleman

[Tom Saurus]

guns1inger: Thank you for the information you provided. The picture still remained sharp after you put it through virtualdubmeg2. I think it would be wise for me to just forget about using Womble to export .avi's; atleast until I understand it better.

FulciLives: I just encoded a short clip that was 720x480 that didn't have black bars at the top or bottom and it did not look good when it was converted to XVid. So I see what you meant about interlacing become very evident. I will have to experiment somemore and hopefully get a better result. Avi.net doesn't let one adjust anything, you load your file in, and everything settings-wize is greyed out and you get what it decides is best. It seems like letterboxed stuff does better than the standard video we have been used to seeing over the years on our tvs. There was alot of action in the scene I was encoding, actually it was the opening sequence of an episode of Gunsmoke where the show is introduced as Matt Dillon rides in on his horse. It looked fine in Mpeg2 but really yucky in the XVid format. Thank you for your advice. I might try AutoGK. Though reading through the comments in the tool section, one person mentioned there might be some spyware in that program and that kind of scares me.

[manono]

Though reading through the comments in the tool section, one person mentioned there might be some spyware in that program and that kind of scares me.

That was a long time and many versions ago. And you won't have any interlacing remaining. Give AutoGK a shot at your video.

[Tom Saurus]

manano: I downloaded AutoGK, and it did a good job of creating a XVid file for the Phillps 5140 Divx Player. Thanks for the advice.

FulciLives: Thank you for your advice as well.