brew install -v ffmpeg --use-clang

Warning: Building with LLVM, but this formula is reported to not work with LLVM:

Dies during compilation of motionpixels_tablegen

We are continuing anyway so if the build succeeds, please open a ticket with
the following information: 2336-10.7. So
that we can update the formula accordingly. Thanks!

If it doesn't work you can try: brew install --use-clang

==> Downloading http://ffmpeg.org/releases/ffmpeg-0.8.7.tar.bz2
File already downloaded in /Users/alexandrecartier/Library/Caches/Homebrew
/usr/bin/tar xf /Users/alexandrecartier/Library/Caches/Homebrew/ffmpeg-0.8.7.tar.bz2
==> ./configure --prefix=/usr/local/Cellar/ffmpeg/0.8.7 --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --cc=/usr/bin/clang --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libxvid --disable-ffplay
./configure --prefix=/usr/local/Cellar/ffmpeg/0.8.7 --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --cc=/usr/bin/clang --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libxvid --disable-ffplay
ERROR: libmp3lame >= 3.98.3 not found

If you think configure made a mistake, make sure you are using the latest
version from Git.  If the latest version fails, report the problem to the
ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
Include the log file "config.log" produced by configure as this will help
solving the problem.
==> Exit Status: 1
http://github.com/mxcl/homebrew/blob/master/Library/Formula/ffmpeg.rb#L59
==> Environment
HOMEBREW_VERSION: 0.8
HEAD: 2cd086421ee5b01e3684a938795d4d8c12979db7
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CELLAR: /usr/local/Cellar
HOMEBREW_REPOSITORY: /usr/local
HOMEBREW_LIBRARY_PATH: /usr/local/Library/Homebrew
Hardware: 8-core 64-bit sandybridge
OS X: 10.7.2
Kernel Architecture: x86_64
Ruby: 1.8.7-249
/usr/bin/ruby => /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
Xcode: 4.2.1
GCC-4.0: N/A
GCC-4.2: build 5666
LLVM: build 2336
Clang: 3.0-211.1
MacPorts or Fink? false
X11 installed? true
==> Build Flags
"--use-clang" was specified
CC: /usr/bin/clang
CXX: /usr/bin/clang++ => /usr/bin/clang
LD: /usr/bin/clang
CFLAGS: -O3 -march=core2 -w -pipe
CXXFLAGS: -O3 -march=core2 -w -pipe
MAKEFLAGS: -j8

Error: Failed executing: ./configure --prefix=/usr/local/Cellar/ffmpeg/0.8.7 --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --cc=/usr/bin/clang --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libxvid --disable-ffplay
These existing issues may help you:
    https://github.com/mxcl/homebrew/issues/8456
    https://github.com/mxcl/homebrew/issues/8815
Otherwise, please report the bug:
    https://github.com/mxcl/homebrew/wiki/checklist-before-filing-a-new-issue
We saved the configure log, please gist it if you report the issue:
    ~/Library/Logs/Homebrew/config.log