I hate to start the post like this, but I'm blind and I would need your help.
I have a couple TV-series on DVD I would like to share with friends. I got the idea to convert them to MP4/X264. I use Megui for the job.
I have already converted 2 thirds of the videos, but I have been thinking about it and now I'm not sure if my rips are good. Because I can't check the result visually, I have to rely on everything Megui tells me. I have read a lot of posts and I know that in some cases ripping tools can be wrong, but let's just assume that everything Megui tells me is correct, OK?
Megui reports the DVDs as being 16:9 PAL. When I use the autocrop feature no black borders are detected, I don't know how frequent it is, but I have read that such DVDs do exist and so I assume thas theoretically this is still ok.
The most interesting thing happens when I tick the resize box. I want to keep the highest resolution possible. By default Mod 8 is selected which would give me the resolution 720x392 after conversion. In my previous rips I have always selected Mod 16 instead to preserve more pixels. This resulted in 720x400 videos. My question is, is this OK? I know that it is OK mathematically, but the thing that confuses me is that 720x400 is a 9:5 aspect ratio. Should I use mod 2 or mod 4 to get to 720x404 if possible? In other words, apart from losing more pixels are there any other drawbacks connected with an aspect ratio change like this. I have read somewhere that mod 16 resolutions are generally better, but than again maybe those few extra pixels are worth it and I would get 16:9 if I'm not mistaken.
I know that it is difficult to answer these questions without actually seeing the videos themselves, but I hope that it's not impossible. I can make screen shots if needed.
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Better read the forum rules about 'Fair Use'
Yiu can rip for yourself and immediate family. Sharing with friends is copyright infringement.
OK then, I'll delete all the rips I have made so far and I'll tell them to buy their own copies if they are interested in watching these series.
I'd still like to know the answer to my original question though. I might make a personal backup of something I value in the future.
You only get black bars directly on a dvd if that dvd is 4:3 and the picture is not.
Same if you display a 16:9 picture in a 4:3 frame.
You have already done the maths and the nearest size to actual 16:9 would suffice. But if the picture is not actually 16:9 then you have to compensate for that as well.
Also need to take care when resizing on the vertical since you could get interlacing artifacts. For a PAL 16:9 dvd, the correct resize is 1024*576.
Two things you can do if this really is a 16:9 PAL DVD.
You can just encode the video at 720x576, and then put the video and audio in an MKV with MKVmerge. But set the aspect ratio to 1.777 (16:9). Which is exactly how a PAL DVD player would play this DVD.
Or you can stretch the video in avisynth and encode it already stretched. Which would be ~1024x576. But Megui won't allow this so you have to edit the resize script manually.
I like my first suggestion because it's more idiot proof and you can always change the aspect ratio later, especially when you have to take into consideration that most DVDs follow the ITU ratios and so come with black bars on the left and right which were designed to be hidden on a tube tv. So while the DVD is stretched to 1.82 (16:9 PAL), if you subtract the black bars it should be close to 1.777. Would be easier for you just to do 720x576, and then tell MKVmerge to set the video to 16:9.
You are losing much of the quality by dropping the resolution to 720x400.
Thanks for the help and suggestions, I'm a little bit smarter now, but it will take me some more time to fully understand why and how. I have one more question if you don't mind.
The third option would be to encode the source as anamorphic by checking the relevant checkbox in Megui's Avisynth script creator, right? As far as I know, not all players can play back anamorphic encodes correctly, but why is that?
What's the difference between an anamorphic encode in Megui and an encode where one just stretches the width, for example with the help of a resize filter in an Avisynth script? To me it would seem that it's the same thing, but there must be something different going on under the hood in each of these cases.
MeGUI do that, because then the same aspect ratio is written to the video stream when encoding as is written to the container when muxing. When using the script creator, the preview doesn't display anamorphic video with the correct aspect ratio, but it'll be encoded correctly with anamorphic encoding enabled. Or after creating a script and loading it into the video section for encoding, you can use the video preview to preview it with the correct aspect ratio.
Avisynth profile dropdown box and look for the "upsizing" option. I think it's silly that it's disabled by default.
Without anamorphic encoding you're resizing the video to the correct aspect ratio and it's encoded using square pixels (ie 1024x576). You're not increasing the amount of picture detail at all, but it's encoded at a higher resolution, resulting in a larger file size for the same quality. On the other hand, it'll always display correctly. I always resize to square pixels myself.
On the original mod8 question......
For a lower mod, it's possible the video can be resized more accurately, as there's less restriction on the width and height dimensions. For mod4, they must be evenly divisible by 4, for mod16, evenly divisible by 16 etc.
If you resize a 16:9 picture to 720x400, MeGUI will display a certain amount of aspect error. Resize it to 720x404 and it should show less error as 720x404 is closer to 16:9. When resizing to 720x400 it's necessary to crop a little bit of picture away from top and bottom to resize it without distorting it. So in that case, you'd actually be losing picture by using mod16 (or distorting it if you don't crop).
The mod restriction is a leftover for the days when video always needed to be mod16. Mod8 is usually okay for Xvid encoding, but for X264 encoding, you can use whatever you like. I generally try to stick to a mod4 width to be completely safe but the height doesn't matter.
Even if you don't plan on resizing "up" ie 1024x576, I thionk it's better to enable MeGUI's up-sizing option as then it'll allow you to up-scale a little if need be (ie crop a couple of pixels from one side and resize back to 720). When upsizing is disabled, it's a lot more strict about it.
I wouldn't count on the tiny bit of black down the right in the previous screenshot as indicating ITU. Something like this would make ITU more likely:
Black down the sides increases the likelihood of ITU and a lack of it makes exact 16:9 more likely, but there's no guarantee either way.
Last edited by hello_hello; 23rd Jul 2015 at 11:03.
Also, how accurate is Megui? Can I believe it when it tells me that the video is 16:9 and that it doesn't have any black bars? If it's accurate everything's fine, but if it's unreliable I will always need the help of a sighted person when ripping DVDs.
Sorry for all these questions. On the bright side, I guess I won't have more after this.
MeGUI takes any cropping into account when calculating the aspect error if you resize. Sometimes you might need to adjust the cropping a little manually to reduce the aspect error as much as possible, which might involve cropping a few pixels of picture here and there. It depends on the resolution you're resizing to and/or the selected mod. It should be easy enough to confirm. If you resize a PAL non-ITU 16:9 DVD to 1024x576 the aspect error should be zero. It'll also be zero if you resize to 960x540 or 704x396 or 640x360, because they're all exactly 16:9. If you crop a few pixels from the top or sides and resize to 1024x576 MeGUI should display an aspect error. Resize to 960x540 or 704x396 or 640x360 with the same cropping and the aspect error will be the same each time because they're all the same aspect ratio. The resolution you resize to doesn't matter, as you adjust the cropping and/or resizing, MeGUI will display the correct aspect error. The idea is to get it as close to zero as you can.
Pretty much all 4:3 DVDs are ITU. Even ones without black bars at the sides. If a 16:9 DVD has no black bars each side, or just a couple of pixels worth, it's probably non-ITU. If there's substantial black bars (8-10 pixels or more each side) it's very likely to be ITU. Other than that all you can do is resize the video to square pixel dimensions using one Input Aspect Ratio or the other (16:9 or ITU 16:9) and look for straight on shots of objects that should be either perfectly round, or perfectly square, and see which resizing method gets them the closest to round or square. You can drive yourself nutty though.....
As far as cropping goes, it's personal choice. The cropping itself doesn't alter whether a particular DVD is ITU or non-ITU. I always crop because not all DVDs have nice clean edges between the picture and the black borders, so I prefer to crop until the edges of the picture are nice and clean. As I said, MeGUI will still work out the aspect error correctly when resizing to square pixels.
AutoCropping tends not to crop too enthusiastically so if anything it tends to leave a line of black pixels uncropped. If you're fussy, you'll need to check it yourself.
If you want to use anamorphic encoding, enable it and choose the "encode non-mod16" option (to begin with). It's badly named (left over from the dark ages when MeGUI could only resize to mod16 dimensions) because it'll let you encode using any mod, including mod16. Resizing will be disabled. You can still crop, and if you do, what's left will be encoded "as-is". Anytime you do crop you change the aspect ratio. Think of it like this..... if you take a 16:9 picture and crop half the height, what's left must be 16:4.5, or 32:9. It can't still be 16:9 because half the height is gone. As you adjust the cropping with anamorphic encoding enabled and you switch to the Script tab in the script creator, you'll see the display aspect ratio at the top changes. MeGUI uses that to set the correct aspect ratio when encoding, so once again you can crop away and let MeGUI take care of the rest. All you need to do is decide which Input DAR you want to use.
The other anamorphic options mostly let you set a mod, and MeGUI will automatically adjust the cropping to make sure you stick to it. There's only one which lets you resize and that's the "resize to selected mod" option.
When using anamorphic encoding, resizing normally doesn't effect the aspect ratio (which is a bit counter-intuitive given it sets the aspect ratio when resizing to square pixels). You can think of it like this.... if you take a PAL 16:9 DVD that's exactly 16:9 you can encode it at 720x576 while setting a 16:9 aspect ratio and it'll display correctly. It can only display correctly if it's 16:9. So you could resize it to 1024x400, or 860x240, or 600x1020.... anything you like.... as long as you set the 16:9 aspect ratio when encoding it'll display correctly. If you resize when using anamorphic encoding, you're just changing the resolution, not the aspect ratio. The main point of anamorphic encoding is not to resize though..... to encode the video using the same shaped pixels as the original, so if you do resize, you'd probably not resize very much.
Anyway, even if you use the "resize to selected mod" anamorphic option and resize and crop, MeGUI will still take care of the aspect ratio calculations.
There's an option in the Avisynth profile configuration labelled "acceptable anamorphic aspect error". It's set to 1% by default. It allows MeGUI to fudge the aspect ratio a little when using anamorphic encoding, I assume to make it easy to achieve a nice even 16:9 or 4:3 aspect ratio after cropping. It's 1% by default, which is why the script creator might display a small aspect error when using anamorphic encoding. If you change it to 0%, MeGUI won't fudge the aspect ratio at all, and no matter how you crop or resize when using anamorphic encoding, the aspect error displayed should always be zero. It only effects anamorphic encoding.
Last edited by hello_hello; 23rd Jul 2015 at 15:19. Reason: spelling
Megui allowed this. And all this time I've been manually upscaling it. Thanks for that.
It does however, pay to peruse through the changelog after updating MeGUI (under the Help menu) in case you miss any of the fun stuff.
2238 [AviSynth Script Creator] enabled upsizing