$ LANG=C ffmpeg -f v4l2 -i /dev/video0  -f alsa -ac 1 -i default http://rpi:8090/rpi.ffm
ffmpeg version N-60519-g8b0befe Copyright (c) 2000-2014 the FFmpeg developers
  built on Feb 10 2014 20:54:25 with gcc 4.8 (Ubuntu/Linaro 4.8.1-10ubuntu9)
  configuration: --enable-avfilter --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --enable-runtime-cpudetect --enable-libmp3lame --enable-libfaac --enable-nonfree --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libxvid --enable-libx264 --enable-libopencore-amrnb --enable-version3 --enable-libopencore-amrwb --enable-version3 --enable-libdc1394 --enable-libvpx
  libavutil      52. 63.101 / 52. 63.101
  libavcodec     55. 50.100 / 55. 50.100
  libavformat    55. 31.100 / 55. 31.100
  libavdevice    55.  8.100 / 55.  8.100
  libavfilter     4.  1.102 /  4.  1.102
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, video4linux2,v4l2, from '/dev/video0':
  Duration: N/A, start: 4474.318146, bitrate: 165722 kb/s
    Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 720x480, 165722 kb/s, 29.97 fps, 29.97 tbr, 1000k tbn, 1000k tbc
Guessed Channel Layout for  Input Stream #1.0 : mono
Input #1, alsa, from 'default':
  Duration: N/A, start: 1392139433.917741, bitrate: 768 kb/s
    Stream #1:0: Audio: pcm_s16le, 48000 Hz, mono, s16, 768 kb/s
[libvpx @ 0x1886300] v1.2.0
Output #0, ffm, to 'http://rpi:8090/rpi.ffm':
  Metadata:
    creation_time   : now
    encoder         : Lavf55.31.100
    Stream #0:0: Audio: vorbis (libvorbis), 22050 Hz, mono, fltp, 64 kb/s
    Stream #0:1: Video: vp8 (libvpx), yuv420p, 720x480, q=5-42, 400 kb/s, 1000k tbn, 29.97 tbc
Stream mapping:
  Stream #1:0 -> #0:0 (pcm_s16le -> libvorbis)
  Stream #0:0 -> #0:1 (rawvideo -> libvpx)
Press [q] to stop, [?] for help
[video4linux2,v4l2 @ 0x184d1a0] The v4l2 frame is 345600 bytes, but 691200 bytes are expectedp=25
frame= 7866 fps= 22 q=0.0 Lsize=   14076kB time=00:06:05.55 bitrate= 315.4kbits/s dup=4357 drop=25
video:11529kB audio:2124kB subtitle:0 data:0 global headers:4kB muxing overhead 3.076102%
[video4linux2,v4l2 @ 0x184d1a0] Some buffers are still owned by the caller on close.
Received signal 2: terminating.


Seconds later:


[rpi@rpi ~]# ffserver -f ffserver.conf
ffserver version 2.1.3 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jan 15 2014 15:27:19 with gcc 4.7.2 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --enable-avresample --enable-dxva2 --enable-fontconfig --enable-gnutls --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libv4l2 --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-pic --enable-postproc --enable-runtime-cpudetect --enable-shared --enable-swresample --enable-vdpau --enable-version3 --enable-x11grab
  libavutil      52. 48.101 / 52. 48.101
  libavcodec     55. 39.101 / 55. 39.101
  libavformat    55. 19.104 / 55. 19.104
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 90.100 /  3. 90.100
  libavresample   1.  1.  0 /  1.  1.  0
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Tue Feb 11 10:23:52 2014 FFserver started.
[streaming working]
Tue Feb 11 10:29:59 2014 Assertion num < (1ULL<<56)-1 failed at libavformat/matroskaenc.c:179
Aborted (core dumped)