Halo 4

If you are like me, then you are attempting this as a quick achievement. And it is.

I simply went to Forge, the default Haven map, and went into basic editor. I moved one of the spawn points two feet and then went to Theatre. The game saves your Forge interactions, so select yours and then play it. You should see a small menu on the righthand side of the screen. One of the buttons is record, click it, let it record for a few seconds and press stop. Click the Autosave and Name option, and achievement unlocked.

If you want the screenshot achievement too, press pause and click the button in the menu that says "Take screenshot." Save it. Done

I got this by playing online as I was going for the "I <3 Red vs. Blue" and the "Hanging on the Combat Deck" achievement.

But after you play a game online, you go back to the Infinity menu and click the "Theater" mode, and then you select your film, and there will be a "Record" button on it, and you click that, and record for like 2 seconds, then save it.

You can get the "Snapshot!" achievement also, as there will be a button that says, "Screenshot" or something like that, and you just click that, and then save it. Two Achievements unlocked.