AVI to MPEG conversion - stretching problems

[jubbely2]

Happy New Year all!

I am having some problems. I have some AVI files which if I check in windows media player or get a screen grab appear to be 512x384 pixels and 4:3 aspect ratio. Thats fine and the ratio corresponds to 720:540.

This leads me to believe that they were recorded in NTSC format?

My probem is that I can't work out what settings to use in TMPGEnc when converting to a PAL 4:3 standard. Whatever I seem to to, I end up with a vertically stretched picture as TMPGEnc converts to a 720:576 as required.

I understand that this stretching is expected - 540 to 576, sure. But how can I avoid this? I don't mind a black bar on top and bottom to correspond to the extra lines for example, but even if I tell TMPGEnc to Centre and Keep the aspect ratio, I end up with this problem.

This must be a common problem, and I have done some searches, but couldn't find a resolution to this.

Would appreciate any help!

Cheers
Jub

[mats.hogberg]

If the source is 4:3, and you encode it to 4:3 mpg, the mpg resolution is irrelevant - the player should resize it to a 4:3 aspect ratio regardless of resolution. (Both 16:9 and 4:3 DVD's are 720x576 PAL)

/Mats

[jubbely2]

Thanks for the comment Mats, but the picture is definately stretched, so I must be doing something wrong....

[mats.hogberg]

How do you play back the MPG? Seems like not all software players take note of the AR.

/Mats

[jubbely2]

Hi

I am using the MPG created in DVD-LAB Pro, but I noticed what I thought might be some of the pic missing, so I had a look in Media Player. Attached two grabs taken with imageGrab30n to show what i mean:



FROM AVI



FROM created MPG




see how her face is longer?

there is some thin black bands on the left and right, which only seem to be there if i use centre (keep aspect ratio) option

jub

(the loss in quality is another question :0) )

[jagabo]

see how her face is longer?

The number of pixels in the frame does not determine the final shape of the picture on TV -- the Display Aspect Ratio (DAR) does. You are using a player/viewer on the PC that isn't correcting for the DAR. It is simply showing you each pixel of the frame. A 512x384 AVI source should be stretched to 720x576 (PAL) or 720x480 (NTSC) MPEG if you are making a DVD. The DVD player will display these with the proper 4:3 aspect ratio on TV.

Note that the DVD spec for wide screen videos uses the same number of pixels in each dimension -- the player just stretches the picture horizontally to make it wide on a 16:9 TV. Or squishes it vertically (and adds black bars to the top and bottom) for a 4:3 TV.

[jubbely2]

Thanks Jagabo

So you are saying that my DVD player should compensate for this and I wont see the stretching when I play back?

That is good. Thank you.

What about the loss of quality that is seen on the picture? Is this also something to do with how I am viewing the file or will it always happen when I convert avi to mpg?

Cheers
jub

[mats.hogberg]

Every conversion to a not lossless compressed format (like mpg) will result in loss of quality. Generally, for DivX/XviD sources, using an mpg bitrate of about 4x AVI bitrate will do the AVI full justice - a rough but useful rule of thumb. Resizing up like you've done also leads to quality loss - generally, it's better to resize down to nearest DVD resolution.

/Mats

[jubbely2]

Thanks Mats

So what would be a suitable DVD PAL size if I'm starting with a 512x384 avi ?

(I checked it using AVIcodec)

Jub

[jagabo]

Thanks Jagabo

So you are saying that my DVD player should compensate for this and I wont see the stretching when I play back?

Yes, the DVD player will restore the 4:3 display aspect ratio.

What about the loss of quality that is seen on the picture? Is this also something to do with how I am viewing the file or will it always happen when I convert avi to mpg?

Any time you enlarge an image you get blurring. The computer can't restore detail that's not there. But some enlarging filters are better than others. I don't know about DVD-Lab Pro but look to see if there are any options for enlarging.

Some common resizing filters: Bilinear will be the least clear. Bicubic should be better. Lanczos will be even better.

Many people say you should never resize up, you should use the next lower valid DVD resolution. But I disagree with that. With your 512x384 source you can go to 720x576, 352x576, or 352x288. Your DVD player will play all of those the same size on your TV screen. The question becomes: will resizing up look worse than resizing down and then having the DVD player resize up? As long as you used a decent resizing filter and enough bitrate (the larger the frame size the more bitrate you need to retain picture quality) resizing up will look better than resizing down.

Your source video doesn't appear to be all that sharp to start with. You may not notice much difference either way. But if you use a resolution test pattern, or a very clear source, the differences will be obvious. And this also depends on what you're viewing the final result on. A 13" screen won't have enough resolution to see the difference. A 32" or larger screen will.

[mikiem]

"I have some AVI files which if I check in windows media player or get a screen grab appear to be 512x384 pixels and 4:3 aspect ratio. Thats fine and the ratio corresponds to 720:540.
This leads me to believe that they were recorded in NTSC format? "

512 x 384 sizes to both square pixel NTSC 640 x 480 or PAL 768 x 576 maintaining aspect ratios. Easy way to tell, create new image in image editing software at 512 x 384, then resize maintaining proportions. Enter new size of 576 height, get new width of 768 or PAL square pix spec.

To reach DVD spec...

NTSC - resize to 704 x 480 (cropped NTSC accepted by some authoring prog) or 720 x 480 (slight distortion but more widely accepted in software).

PAL - resize to 720 x 576.

PAL DVD player (hard or soft) will automatically stretch frame wider, NTSC will automatically shrink.

Problem as I see it, original grab to me looks too narrow -- maybe see if you can find trailer etc. on-line to compare?

FWIW, correct way to go from DVD, D1 etc to square pixel involves some slight cropping. Perhaps whomever did the original conversion did not? I could be wrong, and would need to see other things in original, but from your snapshot alone I would crop a bit on the sides, and see how that looked sized back to orig. 512 width.

Edit, while I was writing this you got another reply, also correct. I simply wanted to point out something I forgot, and it reminded me -- often I do preview in Power DVD which approximates what the TV will look like.

[jubbely2]

Any time you enlarge an image you get blurring. The computer can't restore detail that's not there. But some enlarging filters are better than others. I don't know about DVD-Lab Pro but look to see if there are any options for enlarging.

Some common resizing filters: Bilinear will be the least clear. Bicubic should be better. Lanczos will be even better.

Many people say you should never resize up, you should use the next lower valid DVD resolution. But I disagree with that. With your 512x384 source you can go to 720x576, 352x576, or 352x288. Your DVD player will play all of those the same size on your TV screen. The question becomes: will resizing up look worse than resizing down and then having the DVD player resize up? As long as you used a decent resizing filter and enough bitrate (the larger the frame size the more bitrate you need to retain picture quality) resizing up will look better than resizing down.

Thanks, can you explain what you mean by the different resizing flters? Is this something that I can set in something like TMPGEnc? DVDLAB-Pro is what I use to author the MPG created, Im not sure anything else happens in there?

[jubbely2]

"I have some AVI files which if I check in windows media player or get a screen grab appear to be 512x384 pixels and 4:3 aspect ratio. Thats fine and the ratio corresponds to 720:540.
This leads me to believe that they were recorded in NTSC format? "

512 x 384 sizes to both square pixel NTSC 640 x 480 or PAL 768 x 576 maintaining aspect ratios. Easy way to tell, create new image in image editing software at 512 x 384, then resize maintaining proportions. Enter new size of 576 height, get new width of 768 or PAL square pix spec.

Thanks Mikiem, I have been doing some searching and I checked using GSpot. The size is 512 x384 which (thanks to you) I know realise could be either PAL or NTSC. However the framerate of 29.97 tells me it must be NTSC.

I keep trying different guides from here for converting to MPG using TMPGenc, but the picture quality always seems poor and the motion jerky. I must be doing something wrong

(I tried to resize to both 720x576 and 352x576 but both seem pretty naff)

I realise my source material isnt all that great, but thats why I dont want to lose any more quality if I can help it.

Here a screenshot of my gspot analysis:



Anyone got any hints on how I can go forward?

[guns1inger]

I would keep it NTSC, as software format conversions are usually far more effort than the results justify.

I would try this script

# -= AviSynth v2.5.5.0 script by FitCD v1.2.4 =-
LoadPlugin("C:\Video\avisynth 2.5\Plugins\aSharp.dll")
LoadPlugin("C:\Video\avisynth 2.5\Plugins\BlockBuster.dll")

AVISource("path_to_source_file")
BlockBuster(method="noise", block_size=8, detail_min=1, detail_max=16)
LanczosResize(704,480,0,0,512,384)
aSharp(2,4,-1,false)
AddBorders(8,0,8,0)

Just cut and paste it into a text file, change the paths appropriately, and save it with the extension .avs (apologies if I an teaching you how to suck eggs). It is a modified FitCD script, similar to one I have used successfully a number of times. You can load this into tmpgenc or cce etc to encode the video to DVD compliance.

[mikiem]

"but the picture quality always seems poor and the motion jerky. I must be doing something wrong" "Anyone got any hints on how I can go forward?"

*Sometimes*, rarely, all that stuff meaning if you have time to kill and don't mind an experiment or 3...

From a lower quality, highly compressed video, it *might* (every once in a while) look better at 352 x 240, using the player to stretch it. If you've got a whole lot of time to kill, there's an article at creativecow on using supersampling in vegas to improve video, though we're talking some hefty render times.

Otherwise do like guns1inger suggested and that should get you there.