In the game I'm making, I'll sometimes need to play videos of the .mp4 format. Does Irrlicht support .mp4 playback? And if so, can anyone recommend a good tutorial on doing so?
Short answer: no.
Slightly longer answer: you can use irrlicht to display video (for instance by updating a texture you're displaying), but you have to handle the decoding in some other way. Based on a quick googling, ffmpeg seems a popular answer.
Here is a thread at irrlicht forums asking exactly the same thing you asked here.
Personally, I'd suggest using some other format than mp4 due to licensing issues, such as xiph theora (cool guys, horrible project names).