Under ideal circumstances, Alleycat Player would work just fine as a simple HTML page loaded into the web browser with no additional support. In fact, you can run Alleycat that way if you choose but there are issues, all of them related to the security model which today's browsers must comply with. I could go on a rant about how this "security model" is poorly designed and shoddily implemented but that won't fix anything. It is what it is and Alleycat Player has to somehow work with it or, rather, work around it.
The core issue is the handling of the HTTP headers in the communication between web browser and server. Some of these headers are "special" and the browser is expected to handle them in a restricted manner so as to prevent "rogue" web applications from compromising the user's privacy or, worse, installing malicious software. The target of these restrictions is the Javascript running inside of web pages. The major security issue is unapproved Javascript accessing privileged information on a web site into which the user is logged (via password or other mechanism). This is what is known as a "cross-site scripting attack" and the main mechanism for preventing such an attack is the HTTP header "Referer" (historically misspelt). Web servers use this header to ensure that an HTTP request is originating from an approved source (meaning the location from which the web page was loaded initially).
It is forbidden on any (approved) web browser for a Javascript program to manipulate the "Referer" header. However, this is the only assurance that the web server has that the HTTP request is genuine. A web browser with a broken security model or a proxy server intercepting the request could very easily change the header. For that reason, a web server will use other methods, such as encrytion, to block unauthorized requests. This is fine except that the "Referer" header is widely abused in cases where user privacy or security is not an issue. That is not surprising but the problem is that the security model implemented in the web browser is so simplistic that there is no way around this abuse without resorting to an external aid. This aid comes in the form of a proxy server.
A proxy server is a third party standing in the communication path between the web browser and the web server. The proxy server is not subject to any of the restrictions implemented in the web browser. The headers and the body of the communication can be freely manipulated. There are numerous proxy servers which are available on the Internet for various purposes but the main purpose is to manipulate the "Access-Control-Allow-Origin" header returned by the web server to the web browser. This is used to indicate to the browser that the data being returned is intended for a specific recipient. It should match the origin of the web page which made the request (the origin being the domain of the server from which the web page was loaded). This process is commonly referred to as CORS or Cross-Origin Resource Sharing.
If the "Access-Control-Allow-Origin" header is set to "*" then this means that the data is not restricted and it may be seen by any web page. This is the minimum that a proxy server will do and most public servers won't do anything else. Some will manipulate the outgoing "Referer" header to be equal to the domain of the destination server. That is pretty much the extent of what a public proxy server will do. I gather that, if they did much more, they would probably get banned by the major browser makers due to the security risk involved.
So the problem for Alleycat Player is that these remote proxy servers are useful for some sites but not for others. That is because the proxies do not support changing the "Referer" header which is what needs to be done for sites which look at this header and refuse service if it is not correct. For example, Twitter requires that the "Referer" header be set to "https://twitter.com" but the actual request to Twitter is in the domain "api.twitter.com". Those proxy servers which modify the "Referer" header to be equal to the destination domain won't work because the domains are clearly different. This is just one reason (there are many more) why a Local Proxy Server is needed in order for Alleycat Player to work to its full potential.
Once you have the Local Proxy Server installed on your system, Alleycat Player will be able to access the various web sites without coming into conflict with the web browser security model. The main trick is to embed some information in the URL in order to inform the proxy server as to what course of action to take. Consider this simple request to Twitter:
The proxy server is located at "localhost" using port number 8080. It is a simple HTTP request though the actual Twitter request is HTTPS. As far as the web browser is concerned, there is nothing special about this URL nor the HTTP request headers. There is no conflict with web security. The proxy server will parse the URL and determine that the "Referer" header needs to be set to a specific domain. Then the request goes out. For the response, the proxy server will change the "Access-Control-Allow-Origin" header to "*" and return that to the web browser. In this case, that is all that the proxy needs to do. Despite how simple this looks, the proxy server has been used to bypass web security in a way that would otherwise not be possible.
Immediately, you might be asking yourself whether this can compromise the overall security of your web browser. It does not and it cannot. I will repeat emphatically for those who don't quite grasp how this all works: It does not compromise your web browser. The Local Proxy Server is no different than any other server on the Internet. It parses a request and it returns a result. It does not sit in the background messing around with your browser or any part of your system. The only potential risk is that a rogue application which knows that you are running a proxy server might try to use it for its own purposes. That possibility is remote but it does not matter to you. Anybody who seriously wants to hack you over the web will certainly have their own servers available for that. There is nothing to be gained from hacking your proxy server. If you are still nervous then what else can I say?
I sincerely hope that you took the time to read my admittedly long explanation before moving to installation. It is important to first understand what this is all about. I would prefer that this not be necessary but it is what it is. Alleycat Player is not a desktop application. It has to work with the web browser. A desktop app would not be any easier to install or use anyway. After all, where would the support come from for displaying the graphics, playing the videos, accessing the Internet and whatever other services which the web browser provides transparently? The only advantage would be not having to write the above explanatory text.
On that note, let's move forward and get this baby installed
The full installation requires installing an application known as "Node.js" which is a web server development platform. It is widely used in many commercial applications. It is public domain software and it is free to use. The complete installation will run to a whopping 50 megabytes. I admit that this feels like a bit of an overkill when Alleycat Player is only 1/4 megabyte by itself. For that reason, it is (and always will be) possible to run Alleycat without the Local Proxy Server, as long as you understand the limitations.
If you already have Node.js installed then go to Step 3.
The Node.js platform is compatible with Windows, Linux, Mac and other systems. My emphasis will be on the Windows version because that is what I have. These instructions may require adjustment for whatever system you are on. The main site for downloading Node.js is here:
https://nodejs.org/en/download
Now you will need to install the files needed to run the proxy server and Alleycat Player.
https://archive.org/download/alleycat-player/installation-v1.zip
At this point, you should have a copy of Node.js and a bunch of Alleycat Player files sitting around on your disk drive somewhere. We just need to get it all working together. If you run the file "alleycat-player.htm", you will just get a web page in your browser but no proxy server. That's fine but you really need the proxy for full functionality.
The proxy server needs to run first and THEN we can run Alleycat Player. If the Node.js installation process did not put an icon on your desktop then find the file "node.exe" where you installed the app. Make a runnable icon with "kraker.js" on the command line and the current directory pointing to it. The details will depend on your system but here's how you can make it work under Windows 10 (earlier versions of Windows may differ slightly).
Open the "Properties" tab on your desktop icon. The "Target" should be the path to the Node.js executable. Add a space character and "kraker.js" to the end of that line. In "Start in", enter the full path to the folder containing the Alleycat Player files. That should do it. You should be able to double-click the icon and get the proxy server running. If it doesn't work, review these instructions to see where you got it wrong.
There are other ways to do this, such as making a batch file, but the basic principle is the same. Essentially, you need to run "node.exe" with the command line "kraker.js" and the current directory needs to point to the "kraker.js" folder. If the current directory is incorrect then the proxy server will either not work or will be unable to find the files for Alleycat Player. When the proxy server finally runs, a console should pop up with this message:
You may get a prompt from your operating system or firewall asking whether to allow access to your network. Node.js only needs access to the Internet and not to your Local Area Network. I have no advice to offer if you are using a VPN or other type of proxy. Either it works or it doesn't, I suppose.
In your web browser, enter the following URL: "http://localhost:8080". You should get a plain-text message indicating that the proxy server is indeed up and running and available to your browser. If this does not work then you should try another browser. If it still doesn't work then you will need to investigate whether there is a firewall or some such device on your system which is blocking the local server. Normally, there should not be an issue.
If you get a response from the local server then try this: "http://localhost:8080/alleycat-player.htm". Alleycat Player should pop up. If so, then you are done with the installation process. If not, then please go back and review the instructions.
You should bookmark Alleycat Player or set it up as your home page.
This is a new feature of Alleycat Player which requires another step if you want to save this type of video. There is a file called "_aliases_sample.txt" in the Alleycat folder which you will want to rename as "_aliases.txt". This is a special file which is needed to enable write access to the local drive. Without this file, it will not be possible to save your videos.
Go to the Alleycat Player instruction manual.
Go to the Local Proxy Server instruction manual.