The Left 4 Dead community has a strange and proud history, similar to that of the Counter-Strike games that L4D evolved from, of taking as many models as they humanly can, roughly rigging them to the Valve skeleton, and shoving them out into the world to wreak havoc. In what other game could a gun-toting velociraptor, Ivan The Space Biker, John Marsden and Slender Man fight a horde of Quake 2 grunts led by a malevolent Diddy Kong? I mean, other than Garry's Mod. There's also a ton of great costume redesigns for the L4D survivors that can come in useful for your movies! And also some not-great ones, but those can come in handy too!

Here's how to get them into SFM, and as a bonus, how to make them unique so you can have five different Ellises in the same room having pillow fights, doing each other's hair and talking about boys.

You'll need the following to do this:

• Source Filmmaker. Obviously.
  
• Left 4 Dead 2. Perhaps also obviously.
  
• A Steam Workshop item that you wish to use in SFM. Any model should work. I haven't tested maps, YMMV.
  
• GCFScape[nemesis.thewavelength.net] for busting open VPKs.
  
• A hex editor. I use Cygnus Hex Editor Free Edition[www.softcircuits.com], so that's what this will deal with.
  
• A general willingness to get your hands slightly dirty with modifying files and such.

For the purposes of this guide, I'm using this Quake 3 model port by Splinks.

Got all that up and working? Good! Let's go.

This first bit is the simplest. Subscribe to your desired mod, let it download, then run Left 4 Dead 2 so that the addon installs. After that, go to your Steam\steamapps\common\left 4 dead 2\left4dead2\addons\workshop and there should be two files with the same bunch of numbers in the name: a JPG of that mod's workshop banner, and a VPK file. Open the VPK file in GCFScape, and extract the models and materials folders to your usermod.

Open the Source Filmmaker SDK, select the model viewer and open the model. If it loads and looks fine, hooray! If it crashes, don't panic. We'll take care of that in a second, while we deal with a slightly pressing issue.

You see, one issue with Left 4 Dead mods is that they actively replace gameplay elements. In English, that means they typically share the same filenames. This makes it tricky if, say, you want to use multiple models that all replace Ellis. This is where the magic of hexing - or modifying a model in a hex editor so that it's no longer a replacement - comes into play. Hexing seems pretty scary at first, and if you only intend on using one such model it's purely optional, but it's actually very easy, so let's cover it right now quickly...

Open your model in Cygnus Hex Editor. You'll see two linked columns - one consisting of just two digit combinations of letters and numbers, and one of the resulting "text".
Don't panic! Let's take this one step at a time.

First off, fixing your model if it's crashing. (You can ignore this bit if it isn't crashing) You'll notice that the first five characters on the right column are something like "IDST,". Click just before the ",", and press "0". You'll notice it's changed from "IDST," to "IDST0". There! Crashing fixed! I told you this was easy.

You'll notice that typing in this hex editor replaces characters instead of pushing text further ahead to make room. Keep this in mind, and also keep in mind that you should not press Backspace or Delete! If you do, hit Undo. If you make a mistake, just click back a bit and type over it.

Now then! See that "survivors/survivor_mechanic.mdl" text in the right column? Click somewhere on it and change it. You're defining a new path and filename for your model to make it unique. You can make it longer (I haven't tested as to how long), and you can make it the same length. For the purposes of covering as much in this tutorial as possible, let's make it shorter. Click at the start of the "survivors/" and let's type... say... "quake3/doomguy.mdl".

As you do this, watch the left hand column. The letters and numbers will change as you type. Watch what two-digit number changes when you type that last "l" (it'll turn into a "6C"), then click a little to the right of it. Now hold down the "0" key to blank out the remainder of the longer filename. Save.

Now, move and rename the model files to fit the new path you just defined! Otherwise the engine won't be able to find them.

Finally, load the model in Model Viewer and check that everything's good. If something's broken, don't stress it. Just re-extract the model from the VPK and give it another shot! It can take a little bit to adjust to.