Why do most people crop out the black bars when ripping a DVD?

[KyleMadrid]

Hi all,

I'm about to do a DVDrip for the first time. I have no problem with figuring out how to encode it and everything, but I just wanted to see what the common way of ripping a DVD was. So I went to kat.ph and looked at the details of some of the DVD rips there, and noticed that on the screenshots, there were no black bars. The black bars in the DVD that I want to rip are at the top and bottom, but are only very thin and don't bother me at all.

So anyway, I was wondering why people usually crop out the black bars when ripping a DVD? It doesn't seem to make any difference because when you play back the movie with the black bars cut out, won't the Media Player automatically create black bars at the top and bottom anyway? So can someone explain to me what the point of doing this is, if there really is any?

By the way, the original resolution of the DVD movie is 720x576 and I plan on making the rip with a resolution of 720x405 (without cropping the black bars) is this a good idea?

Thanks in advance.

[aedipuss]

they are normally removed as there is no reason for them. just wasted encoding bits if you are using a square pixel format like 264. and no 720x405 isn't a good choice. all dimensions should be at least mod4 if not mod16.

[KyleMadrid]

they are normally removed as there is no reason for them. just wasted encoding bits if you are using a square pixel format like 264. and no 720x405 isn't a good choice. all dimensions should be at least mod4 if not mod16.

What would be a good choice? 720x400 or 640x360? Are these mod16?

[aedipuss]

mod16 is divisible by 16. so 720x400 if you want to go that way, but 640x360 is mod8 and usable for most things also. if you are using something like vidcoder it is trivial to also crop off the unneeded black borders.

[KyleMadrid]

so is 720x400 a good resolution for the 16:9 aspect ratio?

[El Heggunte]

Unless you're encoding to MPEG-2, there really is no good reason to avoid mod4 resolutions.
I would use 704x396 (which is exact) instead of 720x400 (which is just an approximation).

[KyleMadrid]

ok, I understand.

Thanks guys

[Cornucopia]

they are normally removed as there is no reason for them. just wasted encoding bits if you are using a square pixel format like 264. and no 720x405 isn't a good choice. all dimensions should be at least mod4 if not mod16.

As they are BLACK and don't change from frame to frame, they actually DO NOT waste encoding bits!
Which is why I have been saying all along to leave them alone unless you have a better reason than that.

Scott

[KyleMadrid]

they are normally removed as there is no reason for them. just wasted encoding bits if you are using a square pixel format like 264. and no 720x405 isn't a good choice. all dimensions should be at least mod4 if not mod16.

As they are BLACK and don't change from frame to frame, they actually DO NOT waste encoding bits!
Which is why I have been saying all along to leave them alone unless you have a better reason than that.

Scott

So you think it's best to just leave the black parts as they are, and not crop them out?

This is what I thought too, but just wanted to make sure by asking people who know better.

Because if what you say is true, and they don't actually waste encoding bits, then I see no reason to cut them out.. because even if you do cut them out, when you watch the movie, the Media Player will just automatically create black parts anyway, right?

[El Heggunte]

IF the width (or height) of the black bars is not a multiple of 8 or 16, then the black bars require more bitrate to be compressed (because of the way the video compressors work). This was a concern in the very-first days of DivX and Xvid, when fitting a 2-hour movie on 1 CD-R was all that mattered. But now that HDD space and DVD-Rs and USB sticks are cheap, it's safe and more comfortable to encode with constant-quality ---
--- it's good to not have to worry about bitrate-savings anymore.

[Noahtuck]

So anyway, I was wondering why people usually crop out the black bars when ripping a DVD?

What no one seems to have pointed out, this can not & never will happen!!

Ripping does not change, alter or remove anything other than copy protection!

Anything removed or changed is done during the re-encoding.

And if you are already re-encoding to another format, which is the only reason you should be removing anything, such as the "black bars" it will make no difference if you remove them as long as the AR flag is set correctly as your TV/DVD player/BD Player/etc. will display them correctly and the "black bars" will not be part of the video but just the black area produced by your TV/Monitor where there is no video.

[MOVIEGEEK]

So anyway, I was wondering why people usually crop out the black bars when ripping a DVD?

What no one seems to have pointed out, this can not & never will happen!!

Ripping does not change, alter or remove anything other than copy protection!

Anything removed or changed is done during the re-encoding.

And if you are already re-encoding to another format, which is the only reason you should be removing anything, such as the "black bars" it will make no difference if you remove them as long as the AR flag is set correctly as your TV/DVD player/BD Player/etc. will display them correctly and the "black bars" will not be part of the video but just the black area produced by your TV/Monitor where there is no video.

We have a winner!

Players add the black bars so if you are making a DVD just leave it as is, if you want to watch this on a portable device then only crop non-anamorphic(windowed) content.

http://www.highdefdigest.com/news/show/764

[steptoe]

If you want to keep the quality and high as possible, why not rip the DVD and run in through MakeMKV and convert it to an MKV so its 100% original. In you insist on encoding it, try Vidcoder thats 100% FREE and will easily convert a DVD or blu-ray or pretty much any video source and convert to either MKV or MP4 using x264

Its slower but the quality is better than anything, and YOU can choose what bitrate to set or even the maximum filesize so the bitrate is then adjusted to fit that

So, if you want a maximum filesize of say 2.1GB per rip then VidCoder will adjust the bitrate to match that. And it does get it pretty close. Obviously the longer the film the less bitrate, but x264 is far better than anything, and its FREE

[Island_Dweller]

Section 7.1.3 of this article seems to suggest that cropping gives better quality if a target file size is needed. http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-dvd-mpeg4.html

[jagabo]

There is one circumstance where cropping black borders is helpful: when a widescreen movie is letterboxed on a 4:3 DVD. If you leave the black borders you will end up with a tiny picture both letterboxed and pillarboxed on a 16:9 TV. And the same could happen with 2.35:1 movies on 16:9 DVDs if wider TVs ever become common.

[hello_hello]

I always crop black borders because much DVD or Bluray video has "fuzzy" black borders rather than nice clean black edges and whether it's rational or not they kind of annoy me. Same with any crud down the sides.... but I guess that's as I mainly use a PC for playback and the TV doesn't over-scan when displaying video from the PC (my choice).

Anyone know if the presence of black border effects the way the actual picture is encoded these days? I recall it being an issue back in the early days of encoding because the encoder can't distinguish between borders and picture, which effects encoding decisions in terms of motion etc.... or something to that effect. I can think of at least one instance where I forgot to crop black borders so I re-encoded the video a second time while cropping, and I was surprised when the cropped version produced a slightly larger file size than the uncropped version (same x264 settings and CRF value each time). I might experiment with that one day.

KyleMadrid,
If you're converting the DVD video, what file type do you need for the output and which encoder do you plan on using?
There's 3 ways to resize a DVD (well you can resize it however you like), but using a 16:9 NTSC DVD as an example, generally you'd resize one of three ways (not accounting for cropping):
- Resize "down" by reducing the height of the video to obtain the correct aspect ratio, ie 704x396.
- Resize "up" by increasing the width rather than reducing the height, ie 854x480
- Don't resize at all when encoding and get the player to resize the video on playback just as it would the original DVD. ie encode at 720x480.

Resizing "down" can potentially lose you some detail, while resizing "up" will increase the file size by comparison. The third method (anamorphic encoding) relies on the player understanding aspect ratios in AVI/MP4/MKV files. Not all hardware players do and if not, will display the video incorrectly. Even though anamorphic encoding is technically the best method, personally I just resize up these days so I don't have to worry which player is being used to view the encoded video.

Depending on the encoding GUI you're using, you might only be able to encode using one or two of the above methods. Not all encoder GUIs will tell you how much you're distorting the picture when resizing. It's not hard to do the math, but this resize calculator makes it easier as it calculates it for you while you adjust the cropping and resizing. http://www.mediafire.com/?09v9bldu9a6hm00

Aside from the above, there's 2 different methods used for resizing DVDs. Either resizing to exactly 16:9 (ie 704x396) or resizing using the "official" method, which is actually slightly wider than 16:9. When calculating DVD resizing, the calculator has an option labelled "Use ITU-R BT.601 coeff". It's checked by default. My advice would be to always uncheck it unless you're sure a DVD uses the "official" ITU resizing method. In my humble opinion, most DVDs don't.

[jagabo]

Also, since most people use resizing filters that sharpen the picture, they can get a row of bright pixels (oversharpening halo artifacts) at the junction of the black border and the picture. If the source DVD already has such a bright row it will be accentuated.

16x point resize of Lanczos resizing (left), the original (center), Bilinear resizing (right):



If the black border comes from an analog recording (a VHS cap for example) it will be noisy. That will eat up bitrate.

[hello_hello]

Can the same thing happen at the sides of the video, and even without any black borders? I'm sure I can sometimes see a slightly brighter column or row of pixels even though I know I cropped all the crud. Especially when playing 4:3 video on the TV with the PC (no over-scanning). If I do notice it, it seems to come and go according to how bright the picture is near the edges, so I just assumed it was some sort of renderer oddity. I never considered upscaling video for the TV could have the same effect, although I only use the Bilinear resizer with MPC-HC. Or could resizing the video when encoding still cause a colum/row of brighter pixels, even without black borders?

[fritzi93]

It doesn't seem like wider AR TVs are catching on. Vizio offers one, but I don't know of any others right now.

Anyway, I'm with Scott on this. Borders don't require many bits, not enough to matter much. Though the contrary opinion is just as valid I suppose. So take your pick.

A few months ago, I actually started re-doing my MKVs and quickly noticed that RipBot was giving me occasional odd results when using the autocrop function. Now, I know how to do it, but it's kind of a pain in the butt when doing hundreds of BDs. Then I tried doing Tron Legacy. For some reason, I hadn't noticed until then that there are some aspect ratio changes in the movie. (I wonder why they did that?) At any rate, I dropped that project and leave my MKVs uncropped.

[Cornucopia]

Did some calculations over the weekend and noticed that nearly ALL the usual Film picture ARs, when sized to TV resolutions, will yield Non-Mod16 sizes in at least one dimension. IOW, if, for example, you cropped a 720x480 DVD rip to 2.40 DAR, you'd have 355 as height. Or 1920x1080 BD rip cropped to 1.85 DAR gives a 1038 height. Since they are ALREADY losing their Mod16 efficiency, the only alternative is to crop less (and include some black), or to crop more (and lose some picture, changing the AR). Most wouldn't want to crop MORE, so if you are already going to crop less, you are already going to be keeping SOME black in there during encoding. Well, it's likely the BORDER between picture & black is really the main place where there is going to be any encoding variation. Certainly, a macroblock that is ALL black (and stays that way throughout) is not going to pose any problem to any encoder. So, what you are having to be dealing with is border pixels either way (cropping and leaving a little black, or not cropping at all).

BTW, I also don't advocate "leaving the black alone". If you do have black as part of the encoded picture, I STRONGLY recommend you replace your existing black with NEW, SOLID black, just prior to encoding in the chain. That way, there is no possibility for encoders to misunderstand and falsely allocate more than an extreme minimum of bitrate to it. Kind of like what a TBC does with sync, but just doing it with letterboxing instead.
Modern encoding that uses smaller macroblock sizes won't have to worry about this as much either way (cropping or not), but I really don't like the idea of a whole array of non-standard sizes being available. If you have a standard size - keep it that way, I say. Less possibility of resizing artifacts or other support problems.

Scott

[DarrellS]

I've noticed that a lot (probably most) DVDs don't have those black bars and if you use a player like PowerDVD that it plays the movie the way that it's supposed to look and doesn't show the black bars. I've also noticed that some editors add those black bars when converted to something else which is why a lot of movies that you download have those black bars.

As Jagabo mentioned also, when watching older movies on a new TV, you see the the overscan lines and extra pixels that the older 4:3 TVs covered up and need to be cropped to remove them from the sides and top and bottom or they look like crap when watching on a new TV. If you're going to re-encode these movies to play on your new TV then you might as well cut out all the crap that you don't want to see and if you're going to convert them to something else, don't use an editor that automatically adds the black bars. I use Virtualdub, the best editor on the market and it's free.

[Cornucopia]

You know, it occurred to me: it would be easy to do a simple test to see just how much bitrate letterboxing consumes. Just rip a BD title (one that has letterboxing already existing), encode (using an AVISynth script) to x.264. Then encode from the rip again (using the same AVISynth script, but this time crop+pad instead of just crop) to x.264 (only difference in the x.264 settings should be the dimensions). Use CRF encoding on both, set to the same factor. The filesize difference between the 2 SHOULD account for the bitrate necessary to encode the black.

Somebody else can do this right now...I have too many things on my plate, ATM. Have fun! Should be fairly definitive & objective comparison.

Scott

[jagabo]

You know, it occurred to me: it would be easy to do a simple test to see just how much bitrate letterboxing consumes.

I've done it in the past. It's tiny (as long as there is no noise in the bars), on the order of 1 percent. Not worth worrying about. The additional encoding time is minimal too. The other criteria discussed above should be your deciding factors.

[Cornucopia]

Thank you! That's what I've been trying to explain here.

Scott

[hello_hello]

Did some calculations over the weekend and noticed that nearly ALL the usual Film picture ARs, when sized to TV resolutions, will yield Non-Mod16 sizes in at least one dimension. IOW, if, for example, you cropped a 720x480 DVD rip to 2.40 DAR, you'd have 355 as height. Or 1920x1080 BD rip cropped to 1.85 DAR gives a 1038 height. Since they are ALREADY losing their Mod16 efficiency, the only alternative is to crop less (and include some black), or to crop more (and lose some picture, changing the AR). Most wouldn't want to crop MORE, so if you are already going to crop less, you are already going to be keeping SOME black in there during encoding.

I think you may have left out an entire category of people who simply encode non-mod16 there.
As losing a little bit of encoding efficiency hasn't been something I've thought about since discovering the joy of non-mod16 encoding, I've never bothered testing it, but I'm running a few encodes at the moment just to see what the result will be. Not that it'll change the way I encode unless I find non-mod16 increases the file size fairly dramatically, which I suspect won't be the case.

To my way of thinking, nothing much changes according to whether you crop, or don't crop, or replace the black borders with new ones (which I do myself on the odd occasion I want to keep them for hardcoding subtitles etc), because the same thing applies either way. It's very common for me to find myself cropping 74 pixels from both the top and bottom of a PAL DVD when encoding, or sometimes it's 76 and 72 etc, but it's quite unusual to be cropping exactly mod16 worth of non-picture area and not still having to make the same "crop a little more" or crop a little less" decisions before adding back the black borders.

I'm pretty sure I can say without fear of being wrong, I've never encoded video from a disc without cropping something during the process. For DVD video it might only be a row of pixels top and bottom to remove the half lines of picture, or 2 pixels from the left and four from the bottom etc.... but always something, and in the case of DVD video (and in my case Bluray video which I generally encode while resizing to 720p) the fact that I'm invariably going to be resizing one way or another when encoding can at least be used as an advantage. For DVD video if I'm only cropping a small amount I generally crop a few more pixels here and there which I'm never going to miss, which returns the aspect ratio to 16:9, and I can then encode using exact 16:9 dimensions. Even mod16 ones if it doesn't take much extra resizing to get there, but the only time I fuss about it is for 16:9 or 4:3 video. If the picture uses a wider aspect ratio then I just encode what's left after cropping, either anamorphically or while resizing to the correct aspect ratio first.

I'll also confess I don't see the validity of "standard size" encoding, as aside from the limitations of DVD and Bluray compliant aspect ratios (and broadcast resolutions) I'm not sure there's really any standard I should be adhering to. Apparently there wasn't one when I was encoding with Xvid and even today, DVD video resized to 704x400 when encoding plays just as well as video resized to 656x368. The world kept turning despite AVI aspect ratios being typically "non-standard", aside from maybe keeping them mod16, so I don't see the logic behind using "standard" resolutions and aspect ratios when encoding with x264. If non-mod16 encoding had ever caused me playback problems I wouldn't do it, but it never has, regardless of the device. Well I lie a little there.... I did notice at one stage DXVA decoding would sometimes produce row or column of green pixels if the video wasn't mod16 and if I was using the Overlay Mixer with MPC-HC. I don't know who to blame there... the renderer, player, or video drivers etc... but aside from that one time every device I've used has played non-mod16 video just as it would mod16.

Anyway... each to their own. I'm in the middle of encoding some old 4:3 DVDs at the moment while cropping and resizing to 640x480 so I've created some new scripts to see how things change according to dimensions. One script simply resizes to 640x482, another resizes to 640x480 with 16 pixels worth of black border added back to total 640x496, and a third which resizes the video to 640x482 again while only adding 14 pixels worth of black border. Once the encoding has finished, I'll report back with the results.

[hello_hello]

I've noticed that a lot (probably most) DVDs don't have those black bars and if you use a player like PowerDVD that it plays the movie the way that it's supposed to look and doesn't show the black bars. I've also noticed that some editors add those black bars when converted to something else which is why a lot of movies that you download have those black bars.

I'd be willing to argue very strongly that almost all the video you'd "download" is encoded without black bars, but I guess it might depend on where you're getting it. It's very uncommon for "torrent" video to be encoded without cropping, although a small majority of people do encode that way.

What you're saying about PowerDVD doesn't make sense to me. If DVD/Bluray video uses an aspect ratio wider than 16:9 it's physically impossible for it not to be encoded with black borders, which means probably more DVD is encoded with them than without. What's your definition of "plays the movie the way it's supposed to look" because whether the black bars are encoded or added by the player on playback the result should be exactly the same. Off the top of my head the only way I can imagine the result being different is if a player isn't using the correct luminance level according to the monitor/TV it's connected to, in which case the encoded black bars might look dark grey while black bars being added back on playback might actually look black as they're supposed to.

As Jagabo mentioned also, when watching older movies on a new TV, you see the the overscan lines and extra pixels that the older 4:3 TVs covered up and need to be cropped to remove them from the sides and top and bottom or they look like crap when watching on a new TV. If you're going to re-encode these movies to play on your new TV then you might as well cut out all the crap that you don't want to see and if you're going to convert them to something else, don't use an editor that automatically adds the black bars. I use Virtualdub, the best editor on the market and it's free.

Well not that I've tested a huge number of TVs, but every Plasma/LCD TV I've met has had over scanning enabled by default. Even though they mostly have a 16:9 aspect ratio, if you change the aspect ratio in the TVs settings to 4:3 it'll display the video with black borders down each side while still over scanning so you don't see the crud. Well the two TVs in this house do. Connecting a PC to a TV or monitor might be a different story because generally for a TV you'd connect a PC at the same resolution all the time (ie 1080p) and so the player/PC would be up-scaling the video while the TV just sees 1080p. And of course PC monitoprs don't over scan like TVs do.

Some encoders automatically add black borders when encoding if necessary, because they're either designed to encode video for DVD/Bluray, or they're clever enough to know they need to do so when encoding video to create a DVD/Bluray compliant disc, but if an encoder isn't specifically designed for that job then generally it won't. If a GUI is designed to create DVD/Bluray complaint discs and it adds black borders when the input video is something other than 16:9 (or 4:3) then that's a good thing as that's what it should do.

Not that I'm disagreeing with the idea of cropping black borders and unnecessary crud when encoding as that's the way I've always done it.

[hello_hello]

Here be the results of my little encoding tests for what it's worth. 40 minutes of video, cropped the same way, with the resizing changed a little, and/or a black border added. Default settings with x264 "slow" preset and CRF18.

Resized to 640x480: 626.8MB
Resized to 640x482: 645.8MB
Resized to 640x480 with 16 pixels worth of black border at the bottom to output 640x496: 629.6MB
Resized to 640x482 with 14 pixels worth of black border at the bottom to output 640x496: 632.3MB

I don't have the motivation required to open each encode to see if they were encoded differently.... at least not at the moment. Assuming the actual video was encoded the same way each time, a non-mod16 height increased the file size a little more than I expected. I'd thought the 640x482 encode would produce pretty much the same file size as the encodes with the black border added, given the actual picture area for one of those was still 640x482, yet it appears it requires less bitrate to encode a 14 pixel black border than it does not to encode anything... which doesn't seem logical to me. Later on I might try a 640x498 encode to see if the extra 2 pixels causes the bitrate to jump again. If it does, I guess non-mod16 does increase the bitrate more than I thought it would, although not enough to stop me encoding that way. If the bitrate doesn't jump again, then I guess the presence of the black border must be effecting the over-all encoding decisions. I've really got to get some sleep now though.

[hello_hello]

I ran two more encodes. This time I just added a couple more pixels to the height of the encodes with black borders to make them non-mod16. So here's all six encodes:

Resized to 640x480: 626.8MB
Resized to 640x482: 645.8MB
Resized to 640x480 with 16 pixels worth of black border at the bottom to output 640x496: 629.6MB
Resized to 640x482 with 14 pixels worth of black border at the bottom to output 640x496: 632.3MB
Resized to 640x482 with 16 pixels worth of black border at the bottom to output 640x498: 632.6MB
Resized to 640x484 with 14 pixels worth of black border at the bottom to output 640x498: 634.1MB

If this was something likely to change the way I encode I might run some more test encodes, however as it's not likely to I won't get any more enthusiastic.
It seems odd though.... I've effectively resized a video to a mod2 height (encode #2), then encoded it a second time while adding a 16 pixel black bar to the bottom (#5), yet even though the height was still mod2, doing so decreased the bitrate instead of increasing it.

[hello_hello]

Is running encodes to test theories a way to put an end to participation in a thread?

Well I was encoding some DVDs today so I thought I'd run a few more test encodes. This particular DVD was PAL and required no cropping from the sides and almost mod16 cropping from the height which is why I used it for testing. I encoded 1 hour from the middle of the movie using nothing but x264's default settings and CRF18.

The first time, I cropped and resized the way I normally would when encoding. In this case, 70 pixels of black from the top and 70 pixels of black from the bottom, then resizing the width to the correct aspect ratio.
The second time I did exactly the same thing, except I cropped 72 pixels from the top and bottom to make it mod16.
The third time I cropped 72 pixels top and bottom again, then added the black borders back with AVISynth.
And just to satisfy my curiosity, encoded 1 hour of nothing but the black. No picture at all.

1024x436 (mod4 height) produced a file size of 810.0 MB
1024x432 (mod16 height) produced a file size of 810.6 MB
1024x576 (black borders added back) produced a file size of 800.2MB
1024x144 (nothing but black) produced a file size of 2.1MB

So once again it appears any non-mod16 inefficiency isn't anything to worry about, and once again, the actual picture must have been encoded slightly differently in the presence of black borders, given the bitrate dropped a little.
I don't quite understand why the mod16 1024x432 encode finished up being marginally larger than the mod4 1024x436 encode, given the latter also has a couple more lines of picture. That doesn't make complete sense to me.

When it's all said and done though, there doesn't seem to be any reason to encode with or without borders, mod16 or non-mod16..... aside from personal preference.

[Selur]

small side note: one could also compare the encodes, when encoding to x264 lossless.
But I agree with hello_hello, when using x264 on a source with clean black bars, cropping the bars normally (when using 2pass or crf) only makes an unimportant difference. (same goes for the resize mod)