FFMPEG FLV1 Convert Error

 ffmpeg -i /tmp/open-uri20130218-25320-1rb781j.flv sample.mp4
ffmpeg version git-2013-02-08-0d194ee Copyright (c) 2000-2013 the FFmpeg developers
  built on Feb  8 2013 13:03:19 with gcc 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)
  configuration: --enable-gpl --enable-libass --enable-libfaac --enable-libfdk-aac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-x11grab --enable-libx264 --enable-nonfree --enable-version3
  libavutil      52. 17.101 / 52. 17.101
  libavcodec     54. 91.102 / 54. 91.102
  libavformat    54. 61.104 / 54. 61.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 35.101 /  3. 35.101
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, flv, from '/tmp/open-uri20130218-25320-1rb781j.flv':
  Metadata:
    creationdate    : Sun Feb 17 17:07:39
  Duration: 00:00:09.93, start: 0.000000, bitrate: 166 kb/s
    Stream #0:0: Video: flv1, yuv420p, 320x240, 1k tbr, 1k tbn, 1k tbc
    Stream #0:1: Audio: speex, 16000 Hz, mono
File 'sample.mp4' already exists. Overwrite ? [y/N] y
Invalid sample format '(null)'
Error opening filters!