

Mac OS Screenshot does not Allow DVD Player to Appear in Captured Region - JacobIrwin
http://jacobirw.wordpress.com/2013/05/30/mac-os-screenshot-does-not-allow-dvd-player-to-appear-in-captured-region/

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cjbprime
Linux does the same thing. In the case of Linux/X11, it's because an
accelerated video overlay is being used -- instead of writing to a framebuffer
that's then rendered onto the screen, you coordinate with the video card to
have it handle scaling, colorspace conversions and blitting of that data
directly onto a memory-mapped portion of the display.

Then the screenshot tool runs and dumps the framebuffer, and finds no image
where your DVD playback is happening, because there isn't anything in the
framebuffer for that window.

~~~
jstanley
Thanks for that. I (and I guess a lot of other commenters) hadn't considered
that there might be a totally innocent explanation.

Come to think of it, I've noticed this behaviour in the past.

~~~
shadesandcolour
Well why should you consider something like that when it's easier for the
other commenters to just assume that it's some draconian company with horrible
intentions?

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cs702
Could you ever imagine buying a house that doesn't allow you to perform
certain activities inside its walls, because the architects and engineers who
built it disapprove, and they're fully in control of it?

Neither would I. It wouldn't be _true ownership_. Yet that's exactly what's
happening here. The OP bought a Mac, but he can't perform certain activities,
because the company that built it disapproves, and they control his machine.

"Your" Mac does what you want, but only if Apple and its partners are OK with
it. Is it really "yours?"

~~~
bpatrianakos
That's overblowing it a little bit. Has anyone tried doing the same thing with
third party DVD playback software? I haven't but I think chances are good that
it'll work.

This sort of thing is just par for the course and I see no reason to be upset
over it (not saying you are, just generally). You've got a for-profit company
with close partnerships and deals with various media companies plus their own
iTunes store. Of course this is going to happen. But is it a big deal? It's
sure a pain in the ass if you really need a screenshot of the DVD you're
watching but if you really need it you'll find a way around it.

~~~
cabalamat
> But is it a big deal?

It's a deal breaker for me. My present computer doesn't have a DVD drive, but
even if it did, I wouldn't buy or use a DVD unless I'm in control. I would
rather download from BitTorrent -- not only is it free as in beer it is also
free as in freedom, which is more important.

Computers are already ubiquitous and this will only get more true. If they do
what governments and corporations want instead of what their users want, then
they will become a massive tool for oppression, an oppression more fine-
grained than anything Hitler or Stalin dreamed of.

Treacherous computing is an evil, and all good people should have nothing to
do with it.

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veidr
Extremely annoying and similar: if a Mac is playing back purchased content in
iTunes, any anybody has a Remote Desktop connection to that Mac open, it will
show that same checkerboard "fuck you, consumer peon, your corporate overlords
prohibit you from viewing this content" view.

This happened to me when we had people over for dinner, somebody wanted to
show some video, we bought it from iTunes (in the dining room while eating),
and it wouldn't play back.

Of course, at that point we gave up so as not to let DRM ruin dinner. Later, I
discovered that it was because somewhere in the house there was a notebook
remoting to the TV mac (normal, since that is how we mainly control it).

I don't think this has any underlying technical rationale (hardware
acceleration, etc); I'm sure it is just a relic of Apple's deals with the
'content providers'.

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robterrell
Not really news... this has been the case since the first Mac shipped with a
DVD player. Wait until he tries to attach gdb while a Fairplay-encoded file is
being played.

~~~
lukegb
What does happen if you try to attach gdb? You can't, or the application just
quits, or do you get some error message? I'm somewhat curious now.

~~~
lordgilman
I think this is the story that the parent was referencing. Here's the story
from 2005 and a kernel module loadable at runtime that gets around the
problem.

<https://blogs.oracle.com/ahl/entry/mac_os_x_and_the>

[http://landonf.bikemonkey.org/code/macosx/Leopard_PT_DENY_AT...](http://landonf.bikemonkey.org/code/macosx/Leopard_PT_DENY_ATTACH.20080122.html)

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kalleboo
It used to actually give you an error dialog box - <http://imgb.mp/jaY.jpg>

It's not due to hardware acceleration, I've never been unable to take a
screenshot of anything else in OS X, I think it's due to how Quartz does its
compositing (everything is a 3D texture, there are no 2D-style overlays).

~~~
workbench
Used to get round it with a terminal command, until Lion IIRC.

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FigBug
Same thing happens on Windows if hardware acceleration is enabled. The video
is decoded and drawn by the video card.

~~~
fmoralesc
But in that case (iirc), the video is displayed as a black square. There's no
window borders here either.

~~~
simias
Well if the video is hardware blended there could be anything in the
framebuffer, so it could be black or checkered, I see no incompatibility.

The lack of borders is definitely harder to explain that way though.
Definitely looks like some form of deliberate "limitation".

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BadCRC
it's not because of hardware acceleration at all. It's actively preventing the
window to be captured (I believe iTunes does some similar). It uses a private
API and an example is here:

[https://github.com/heardrwt/RHAdditions/blob/master/RHAdditi...](https://github.com/heardrwt/RHAdditions/blob/master/RHAdditions/NSWindow%2BRHPreventCaptureAdditions.m)

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matthewmacleod
Rather more annoying, the same issue occurs if Screen Sharing is in use when
DVD Player.app starts.

Needless to say, this is a total pain when controlling a media machine
remotely. VLC's DVD playback is a little ropey in my experience, but at least
it works.

It's the pointlessness of this feature that irritates me. If I wanted to copy
the contents of a DVD, I'd insert it and use one of the squillions of programs
that are freely available to do so. I'm pretty sure I wouldn't take frame-by-
frame screenshots.

~~~
lloeki
> _I'm pretty sure I wouldn't take frame-by-frame screenshots._

Quicktime allows to record a video of your screen. I bet QT leverages the same
framework as the screen capture thing.

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kentwistle
I think if you use VLC you can circumvent this despicable attack upon our
freedoms.

~~~
nwh
Of course, it only applies to the inbuilt DVD Player application.

~~~
Tyrannosaurs
Obviously Apple would have known this.

I wonder if part of the reason they agreed to it is that they knew ultimately
it was, in reality, basically no restriction at all.

~~~
DannyBee
I have trouble seeing it as that complex of a calculus

They wanted to make a DVD player. DVDCCA (or someone) required them to block
screen grabs during playback as a condition of giving them a proper license
for CSS (or something) for their DVD player. They blocked screen grabs during
playback.

I doubt "is this really going to achieve anything" ever entered anyone's mind.
It would just complicate the licensing negotiation for something Apple doesn't
really give a crap about (some random third party app)

~~~
Tyrannosaurs
Thinking as a software developer, if a third party asked me to do something I
thought wasn't a good idea for the end user, part of how heavily I'd push back
on it would be how big a deal it really was to the user.

You may be right though.

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616c
The Windows System Internals book (6th edition IIRC) also mentions that even
debug builds of Microsoft Windows Vista and newer have certain restrictions in
observing the kernel, and seeing CSS decryption keys was the thing they
mentioned in particular.

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supercoder
It's also the case on iOS. You can't screen cap the inbuilt movie player
output. Nor can you programatically grab the bitmap layer contents of the
movie.

~~~
Macha
You could back when I had an iPod Touch 2G, unless the limitation only applies
to iTunes DRMed videos and not your own videos you put on there.

~~~
Cthulhu_
cjbprime's explanation (<https://news.ycombinator.com/item?id=5792745>) could
apply to that one as well; did the iPod Touch 2G have a dedicated GPU chip
yet, or was video rendering done on the CPU?

~~~
supercoder
Everything on iOS is sent as a texture and displayed via the GPU. This has
been happening since iOS 1 / First iPhone.

Macha is actually reporting the opposite, it worked fine. So if it wasnt doing
it on a particular version of iOS it was probably just that they were doing
the extra work to hide it then.

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withad
I've never quite understood this. There are so many simpler and more effective
ways of copying DVDs than using screen capture software (let alone taking a
single screenshot) that it doesn't seem worth the effort to deliberately
block.

~~~
qb45
I guess it's more about "educating" the public that The Content is a holy cow
which can only be watched and admired, solely by paying customers, of course.

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willvarfar
It would be plausible if this was actually that the screenshot code could not
get at the hardware-decoded pixels that are composited by hardware.

This used to happen on Windows laptop screenshots a lot - often chroma-keyed -
and it was how the video on the generation of phones I worked on worked.

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JacobIrwin
@acuozzo I was running dual monitors and was watching the movie on the tinier
MacBook Pro screen. I had no intention of using an image from the film for
anything at all. But I always open both screenshots (two screenshots are saved
to your desktop when you are on two monitors; again, with the shortcut
"CMD+Shift+3") to be sure I delete the one I don't want (i.e. the GUI of the
monitor I don't care about), in this case, I just noticed this empty region
(where the DVD Player app was running) in Preview right before deleting the
image.

@mosteveryoneElse yes, it must be mostly related to DMCA BS. And Apple is just
being overprotective here. Since the DVD Player App is native to the Mac OS,
surely it is mpy difficult to hide 'designated app[s']' windows when a user
takes a screenshot.

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michael_h
I couldn't do this on Windows a while back because hardware acceleration was
on.

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DanBC
That person tried, and failed, to take a screen shot.

If he now installs VLC and takes a screen shot is he breaking DMCA anti-
circumvention laws?

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mmuro
It doesn't matter what type of DVD is playing. It could be one you made
yourself and this limitation would still be in place.

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incanus77
This has been the case for like a decade.

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cmircea
So much for fair use.

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k-mcgrady
This also happens in iTunes. Is it really that big of a problem? Why would you
need to screenshot something you're watching? The OP doesn't say why he wanted
to take the screenshot.

Also, does anyone know the reason Mac OS does this?

~~~
acuozzo
> Is it really that big of a problem? Why would you need to screenshot
> something you're watching? The OP doesn't say why he wanted to take the
> screenshot.

Wait... are you kidding?

Among other things:

    
    
      1  Fair use: Hey, buddy! Check out this cool still.
    
      2  Fair use: Wow, that's a cool shot! I'd love to make it my background.
    
      3  Fair use: Gee, that sucks! Director Martin M. McStupid made a bunch of CGI changes to his classic award-winning 70s film. I'd like to share some of the most offensive changes with my buddies on the Example.net Forum.
    
      4  Fair use: Totally awesome! The DVD9 release of this film was encoded with a high bitrate. Let's take some stills from fast-moving shots so that we can compare it against the DVD5 release from the 90s.
    
      5  Fair use: This movie no longer has its original theatrical color-timing. I'd like to take a sample from each shot so that I can come up with curves to do a shot-by-shot color-correction.

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so898
I think there are more than 3 video player which could play DVD on Mac. So why
we use this BAD application? BTW, the new retina macbook shipped without DVD
driver, there is not that much which we need to worry about.

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paulschreiber
This has been true for years — since Mac OS X 10.1. I believe third-party
tools like Snapz Pro (and perhaps even the command line screen capture tool)
get around this limitation.

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nakedrobot2
It has been this way for years.

VLC is ok of course :)

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mml
DVD player also can't be "seen" over airplay.

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da_n
I'm not sure why, but I always find it irrationally annoying when I see
someone using their desktop as a filesystem.

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markdown
OT: Wow, that's a messy desktop. Makes me feel a little better about my own
desktop.

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robspychala
also happens when you try to view iTunes movies or shows while controlling
your Mac with a remote desktop connection.

super annoying.

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danso
That's funny...I know this has been around for awhile, but I only first
experienced it this weekend when I was trying to excerpt part of a movie scene
(for educational purposes)...I didn't go the Handbrake route because I wanted
to say that I had avoided breaking the DRM law...while the copyright law may
be ambiguous on backups, cracking the DRM is pretty much always a breach of
the DMCA

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superchink
People still use DVDs?

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EvilLook
Hurray for the DMCA!

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youngerdryas
Now is the time for armed revolution, our human rights are being violated. :b

