使用ffmpeg将mp4音频转换为webm - 无法为webm找到合适的输出

Question

我有一个自定义的heroku buildpack,正在安装ffmpeg,libvorbis等.

当我运行时,ffmpeg我得到以下输出:

FFmpeg version SVN-r0.5.9-4:0.5.9-0ubuntu0.10.04.3, Copyright (c) 2000-2009 Fabrice Bellard, et al.

configuration: --extra-version=4:0.5.9-0ubuntu0.10.04.3 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Jan 24 2013 19:42:59, gcc: 4.4.3
At least one output file must be specified

我正在尝试将mp4音频转换为webm音频.

这是我正在使用的命令:

~/public/audio $ ffmpeg -i sample.mp3 sample.webm

并输出:

FFmpeg version SVN-r0.5.9-4:0.5.9-0ubuntu0.10.04.3, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  configuration: --extra-version=4:0.5.9-0ubuntu0.10.04.3 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Jan 24 2013 19:42:59, gcc: 4.4.3
Input #0, mp3, from 'sample.mp3':
  Duration: 00:00:01.56, start: 0.000000, bitrate: 76 kb/s
    Stream #0.0: Audio: mp3, 24000 Hz, stereo, s16, 64 kb/s
Unable to find a suitable output format for 'sample.webm'

这在我的OSX安装上工作正常,但在Ubuntu 14.04上我遇到了这些错误.

我需要做什么.webm文件可以作为目的地？