"Unknown encoder H.264." What do I need?

Question

Hi!
I'm trying to convert an .avi file to a .mp4 file with H.264. When I'm trying to do this I get an error saying "Unknown encoder H.264." What do I need?
I'm using WinFF for the task. I think it uses ffmpeg, but I can't find out how I can make it support the H.264 codec. Anyone?

Answer 1

You all may want to check to see if you're actually producing aac audio with FAAC. Honestly, it's been broken in Arch for months, the solution is known, and it's not being implemented. If you see the last line after faac --help, you're producing mp2 audio:
faac --help
Freeware Advanced Audio Coder
FAAC 1.26.1 (Jul 19 2008) UNSTABLE
Usage: faac [options] infiles ...
Options:
-q <quality> Set quantizer quality.
-b <bitrate> Set average bitrate to x kbps. (ABR, lower quality mode)
-c <freq> Set the bandwidth in Hz. (default=automatic)
-o X Set output file to X (only for one input file)
-r Use RAW AAC output file.
-P Raw PCM input mode (default 44100Hz 16bit stereo).
-R Raw PCM input rate.
-B Raw PCM input sample size (8, 16 (default), 24 or 32bits).
-C Raw PCM input channels.
-X Raw PCM swap input bytes
-I <C,LF> Input channel config, default is 3,4 (Center third, LF fourth)
MP4 specific options:
MP4 support unavailable.