MinecraftMediaLibrary General Information¶
This section is intended for developers and strongly recommended for readers to take a look at if they want to use the library and know what is going on internally.
VLC Media Player¶
The library uses a very common media player today known as VLC Media Player. The reason due to this is because of how efficient the program is to provide callbacks to actual frames in production code. It is able to read an MPEG file and many other video formats allowing it to be flexible, and a very much valid option to choose.
Note
Frame callbacks (as described above) are callbacks where an external library or API sends frame data to your own consumer, allowing you to process the data if necessary. In this case, VLC Media Player is used to send frame data from the MPEG video into our application, which allows easier processing and faster video data retrieval (due to how it is written in C/C++/Lua).
Implementing VLC Into MinecraftMediaLibrary¶
Obviously, VLC Media Player is not written in Java, but mainly composed in C, C++, and other native libraries. Luckily, a project known as VLCJ which provides bindings and a functional API to provide callbacks into Java code.
Warning
While VLCJ is able to provide us with built in video players, there are some drawbacks. For example, VLCJ is not suitable for multiple players at once! Take a look at this post about how the creator of VLCJ (Caprica) attempts to solve this issue by creating “Out of Process” media players. To sum up, some of the libraries VLC uses are not thread-safe and reentrant, causing them to create fatal crashes. This means multiple concurrent threads (or video players) accessing such native libraries will likely be unsafe.
Due to such restrictions, MinecraftMediaLibrary as in the current patch does not support multiple video playback at once. It is unsafe and not ready for production. However, in the near future, perhaps VLCJ - Pro could be an option.
Handling VLC Binaries¶
This is arguably one of the hardest problems I had to solve – giving support to multiple platforms. Not everyone will have VLC installed on their PC. I had to find a way to fix or bypass this issue. Unfortunately, VLC uses binaries that are dependent on the Operating System of the environment. This means that Windows, Mac, Linux (and even separate Linux Distributions) have their own binaries to use.
Note
For information about how I implemented a solution to install the binaries for the users, take a look below.
Loading VLC Binaries¶
Loading VLC binaries is a separate issue as each operating system requires it’s own method of loading the VLC binaries. After installing the binaries for the user, we must load them properly in order for the library to use them properly.
Note
VLCJ provides a great strategy for loading called NativeDiscovery however, due to how Minecraft servers function, this method will not work.
To go into more detail on why NativeDiscovery does not work, the method uses ServiceLoader to find and load the possible directories. The class which uses ServiceLoader can be found here. According to StackOverflow, ServiceLoader will only find certain classes loaded by the current classloader thread. After a load of debugging, I’ve finally found that due to how the Minecraft server is running on a different classloader thread from the actual library, it can find the proper paths. Thus, I had to implement my own mini-NativeDiscovery implementation to try and load VLC. This discovery method is known as MinecraftMediaLibrary NativeDiscovery, or MMLNativeDiscovery in short.
MMLNativeDiscovery¶
I created separate abstractions for each module. In order to load VLC binaries, I created a method which takes in a directory and attempts to load VLC from that directory. It uses recursion to locate the plugins folder and the folder containing core libraries of VLC (such as libvlc, libvlccore, etc). The strategy/algorithm can be found here.
It first tries to identify if NativeDiscovery works on the system or not (which we know doesn’t work, but maybe it will work some day!). Then, I used a heuristic algorithm to improve the search. I added keywords that sort the PriorityQueue such that files with the keyword would appear at the top, improving overall speed.
Once I found the plugins folder, I set the VLC plugin path relative to that. It sets an enviornment variable that VLC can use. If I found the native library, I also set that up too. Each operating system has it’s own relative paths to set for environment variables and VLC path.
Note
For more information about how I loaded each of the binaries for the Operating Systems, take a look at the links below.