Jay Tuley

What Is WOV¹?

WOV pronounced “wahhv”, stands for Wrapper Of Video, its a Mac OS X package format that contains both a non quicktime video source and a pre-parsed QuickTime reference movie and is QuickLook compatible.

What’s WOV Got to Do With It²?

If you have ever had a large Window Media File you want to open with WMVPlayer plugin for QuickTime, you may have noticed it’s really really slow. Same goes with Perian and MKV’s, though not nearly as bad. Since they are converting to a QuickTime movie format in memory its possible to save that file and have much quicker load times with subsequent opens. However you must be careful, because these plugins can (and have in the past) changed they way they work such that imported quicktime movies can be broken with updates, so it’s imperative that you don’t save self contained movies only reference movies external to the original file. So thats what WOV does, it keeps a reference movie which is really small and the original file combined into its package format, that makes it easy to organize these pairs, repair the reference movie if necessary in the future, and completely undo the WOV container and restore it to the original files (if you so desire).

WOV WOV WOV³.

So early on playing around with the idea of WOV, I soon realized it was a good format for simple non destructive QuickTime edits, so I chose one I though was particularly useful which is joining files. So there exists an option, when converting a batch of files in WOV Converter, to combine multiple files into a single WOV file. That resulting package contains a chapter-ized reference movie, the original files, and an M3U playlist of the original files. Thus when trying to open the WOV file in a non native QuickTime App it will try and open the M3U file, I choose M3U since it is so simple it’s likely to be supported in most apps (it is supported in VLC specifically).

Tainted WOV⁴.

There are decent possibilities for caveats with this format, which is why I am putting it out in this early beta and not integrating into NicePlayer right away. One of the obvious caveats is that the original type is masked, which makes it hard to tell if a non native quicktime app is going to be able to open a WOV file ahead of time. I’m not sure if that will be a big deal, but I need people to use WOVConverter & WOVOpener to get feedback to figure out stuff like that.

It should be noted that there is also major issues with using WMVPlayer with WOVConverter. WMVPlayer version 2.2 must have the preference “Open Local Files Immediately” unchecked, or alternatively you must downgrade to version 2.1 to work properly with WOVConverter.

The Book of WOV⁵.

WOVSuite — entirely open source, licensed: MPL/LGPL/GPL

has a few parts:

• WOV Opener — Utility that opens WOV files. You set the actually program you want to open the video and whether that program supports quicktime files natively. Supported on 10.4 & 10.5
• WOV Coverter — Utility that converts any quicktime importable file into WOV files, repairs broken WOV files, and unwraps original files from WOV files too. Supported on 10.5 Only

• WrapperOfVideo.framework — Framework to make it easy for other cocoa applications to support WOV packages without WOV opener. Supported on 10.4 & 10.5

Fun Footnotes

¹ What Is Love

² What’s Love Go to Do With It

³ All You Need Is Love

⁴ Tainted Love

⁵ The Book of Love

Recently Elsewhere

Cocoa collection subclassing | Jens/Log disagrees Faux Collection Class Subclassing | AgentM and both have some bits on class clusters. AgentM’s is a rant about not being able to easily subclass collections, which I am sympathetic too recalling the joy of programing in smalltalk with its rich collection hierarchy. Jen’s is basically a response saying Class Clusters can be frustrating but their okay, just drink the koolade AgemtM. If you explain Class Clusters to someone, they makes sense, but when you try to use Apple’s or don’t know they are there, frustrating things can happen, and I don’t think that it’s really the class clusters fault. Making a composite class by wrapping or forwarding messages isn’t that much of a hassle, subclassing anything requires some knowledge of the class and Apple does document approaches to subclass class clusters, so I’m on the koolade camp on AgentM’s rant. However, I believe there are some bugs in the implementation of a few of Apple’s class clusters that cause many to think that all Class Clusters are evil.

FUD

I think there’s a lot of fear, uncertainty, and doubt in regards to class clusters. There really shouldn’t be though, Apple has a nice page describing the benefits of Class Clusters — Cocoa Objects: Class Clusters

See a class cluster really is really just a sneaky use of a Factory Method (GOF 107) to instantiate a subclass from an abstract superclass. It’s sneaky because its hides it all. alloc, rather than actually allocating, returns a Creator (probably a singleton) and init actually allocates your real product and returns it. As demonstrated here:

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    id obj =[NSArray alloc];
    NSLog(NSStringFromClass([obj class]));
    NSLog(NSStringFromClass([[obj init] class]));
    [pool release];
    return 0;
}

2006-03-17 22:55:15.100 TestDataTypes[6105] NSPlaceholderArray
2006-03-17 22:55:15.101 TestDataTypes[6105] NSCFArray

This is all good, because the classes returned are all subclasses and being the good little object oriented programers we are, we never check what a class actually is. Instead, when need to runtime type check it’s only to determine if it’s a subclass or if it responds to a method or protocol and that should be just fine with class clusters.

If only using standard best practices when runtime type checking would keep us safe, unfortunately a few of Apple’s class clusters, mainly collection classes, are implemented in such a way that they break expected inheritance and expected polymorphism by advertising the wrong public interface for the returned private subclass (I don’t know if this was the case for NeXT or not, but I suspect it wasn’t). I’ll continue with some examples of where this implementation goes wrong.

Dumb Responses from Class Clusters with Multiple Public Superclasses

Here’s a Pop Quiz: What should this statement return?

[[NSArray array] isKindOfClass:[NSMutableArray class]];

Ideally it should return false because when we see the documentation on these public abstract classes, NSMutableArray inherits from NSArray.

However, actually this statement returns true because the private subclasses returned for both public abstract superclasses are the same class inherited from NSMutableArray known as NSCFArray.

Okay so the purpose of having the same class is for easy toll free bridging with Core Foundation, but you know, as long as the instance variables are the same, is Core Foundation really going to care about new methods or a different hierarchy in obj-c land? I’m thinking no in theory, but I’ve not tested and I’m much happier not digging into the C-ness of Obj-C and someone can prove me wrong or right if they wish. However, if you really really wanted to keep the same private class type between the two interfaces, you can always fake the expected hierarchy by making isKindOfClass: call isSubclassOfClass: on the appropriate abstract superclass’s metaclass, and really no one would be the wiser, Core Foundation or otherwise.

That was problem #1, and so you might be thinking to yourself well I don’t test for inheritance with cocoa programing often, most of the time I’ll test for specific methods out of habit, because cocoa programers tend to use informal protocols rather than having deep hierarchies anyway, so it’s not that big of a deal.

So our second pop quiz: What is the result of this statement?

[[NSArray array] respondsToSelector:@selector(addObject:)];

NSArray is not supposed to respond to addObject:. I know that, you know that, but a program is generally going to believe respondsToSelector: over what we think, and respondsToSelector: says true. Of course if you run this line:

[[NSArray array] addObject:@“test”];

you get an exception. Think about when you have a bunch of objects in a collection with various types, some may respond to addObject:, some don’t, and you want to use runtime checking to manipulate them appropriately. How are you suppose to take advantage of polymorphism of this method in this case without being able to trust respondsToSelector:.

There are simple work arounds to these problems, because they are only a handful of classes, but this is clearly a poor implementation of a class cluster, and I haven’t tested every class but I think all Mutable-NonMutable class hierarchies in Foundation on OS X suffer from this bug (Although GNUStep is A-OK from looking at the source), and I don’t think there’s a reason not to fix it, being that they are class clusters, all apple needs to modify are the private subclasses and people aren’t going to be using those methods currently because they return the wrong values that aren’t useful when wrong.

Demonstration of Problem and Fixability

I did write a few Unit Tests to clearly demonstrate this problem with NSArray. It also has a second target called ProperClassCluster that overrides some NSCFArray methods (using categories) to fix responses in inheritance & method testing. In that target I also swizzled the addObject: method to provide an example of returning the correct exception when calling a method that doesn’t exist on an NSArray. A real fix wouldn’t require these hacks, but this works for demonstration purposes. Download ProperClassCluster.zip (20k)

Can Apple do Better than Objective-C?

a language battle royale between C# and Objective-C. I can’t believe after Christmas I get back onto a computer and find out I missed this. I want to jump into the melee but have to go to bed to go to work. But man, this is what I was hoping would have happened at EAA (Rentzsch almost did it).

I think a lot of people are in denial about Objective-C having major short comings. Objective-C is a ton better than C++, harder to compare to C# and Java just because of the static vs dynamic typing philosophies, but very clunky compared with Ruby, Python, and Smalltalk. Objective-C is a very good object oriented C and so if you want C there’s nothing better, but if you don’t care about C it can be an exhausting language because you will be falling back to C a lot (but a lot of that maybe more due to lack of libraries).

Update: Eh, too many people post garbage, ended up with not very interesting comments.

From ridiculous_fish » Blog Archive » Array:

“Don’t second guess Apple, because Apple has already second guessed YOU. In a good way, of course.”

I find the quote highly amusing, and the content of this post on CFArrays illuminating (and I’m just being cheeky with my post title).

So I started making some default scripts and other script examples for NicePlayer. I then realized that I needed keyboard shortcuts on the CocoaScriptMenu. DVD Player’s script menu just uses numbers in order, I don’t like that, another solution I considered was to have some kind of separate config, either gui or text file. However, since renaming is required to order and change the menu text in CocoaScriptMenu, that could get a little complicated.

Keyboard Shortcuts

The solution I settled on was to add the keyboard shortcut itself to the filename. I feel this implementation ended up working really well. The main worry I had was that user error could end up disrupting the host application’s keyboard shortcuts, but the script menu is loaded later than the other menus, so it’s menu shortcuts have the least precedence and thus show up blank if a user tries to duplicate a shortcut. To facilitate adding keyboard combos to file name, I came up with an ASCII representation for the modifiers that kinda look like the real symbols and all require shift to create them (so they won’t reduce the possible representable keyboard short cuts). The symbols are as follows

∗ – Command

$ – Shift

^ – Control

%25 – Option

To create a short cut you add it between two curly braces in the file name before the file extension, ordering the modifiers before the key character, such as Hello World {∗^$H}.scpt for command-control-shift-H.

However after implementing this, I realized most people are going to be using a filesystem that supports unicode, and this can look a lot prettier. So I added support for these shortcuts, not just in the ascii, but using this UTF8:

⌘ – Command (0×2318 PLACE OF INTEREST SIGN)

⇧ – Shift (0×21E7 UPWARDS WHITE ARROW)

⌃ – Control (0×2303 UP ARROWHEAD)

⌥ – Option (0×2325 OPTION KEY)

And you can surround them by LEFT & RIGHT SQUARE BRACKET WITH QUILL (0×2045 & 0×2046) instead of curly brackets. Such as Hello World ⁅⌃⇧⌘H⁆.scpt

While UTF8 looks a bit neater, for safety sake, all my default NicePlayer scripts will use the ASCII way. And the ASCII way is also easier to type, so I’m guessing it will end up being the preferred way, but it’s left up to the user.

You can even add Function Key shortcuts by just typing out {F13} or {⌃⇧F2} or even {∗F16}.

and this scheme should cover a great majority of the possible keys, getting all of them however would require more parsing, which I don’t really see the need at this point, but is possible in the future.

The down side is that I added a new instance variable to the Command classes, so if you do any subclassing of these classes you’ll need to recompile those subclasses with this framework Versioning and Compatibility (not a big deal as CocoaScriptMenu is meant to be embedded not shared).

Count of Scripts

I added a method to the menu generator to count the number of scripts, this can be used to determine whether or not scripts are currently installed.

Panther Compatibility

I did a little bit of hacking to give developers basic usage of the framework under 10.3.9, but I haven’t done any testing with other 10.3ness such as compiling under GCC 3 or actually compiling on 10.3. That said with these compatibility additions there’s a little more work needed when adding support for new filetypes or being more specific with filetypes, as I pretty much just fake the UTI stuff when it runs in Panther and thus more faking or a better solution is required, but if you don’t care about 10.3 then you can continue to not worry about it.

PS

MarsEdit rocks, I wrote this post in it and didn’t have to worry about the UTF8 characters, they were safely converted to html Entities.