$ ffmpeg -y -r:a 30 -i segoyann.avi -t 30 \
         -:v copy -r:a 25 \
         segoyann.temp.avi

ffmpeg version N-72939-g5b0f55a Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --prefix=/home/gliksberg/bin/ffmpeg-build --enable-gpl --enable-nonfree --enable-pthreads --enable-libx264 --enable-libfaac --enable-libmp3lame
  libavutil      54. 27.100 / 54. 27.100
  libavcodec     56. 41.100 / 56. 41.100
  libavformat    56. 36.100 / 56. 36.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 17.100 /  5. 17.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.100 /  1.  2.100
  libpostproc    53.  3.100 / 53.  3.100
[dvvideo @ 0x1c1bc60] AC EOB marker is absent pos=67
[dvvideo @ 0x1c1bc60] AC EOB marker is absent pos=69
Input #0, avi, from 'segoyann.avi':
  Duration: 00:34:37.04, start: 0.000000, bitrate: 28879 kb/s
    Stream #0:0: Video: dvvideo, yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
    Stream #0:1: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Output #0, avi, to 'segoyann.temp.avi':
  Metadata:
    ISFT            : Lavf56.36.100
    Stream #0:0: Video: dvvideo (dvsd / 0x64737664), yuv420p, 720x576 [SAR 16:15 DAR 4:3], q=2-31, 28800 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
    Stream #0:1: Audio: mp3 (libmp3lame) (U[0][0][0] / 0x0055), 48000 Hz, stereo, s16p
    Metadata:
      encoder         : Lavc56.41.100 libmp3lame
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (pcm_s16le (native) -> mp3 (libmp3lame))
Press [q] to stop, [?] for help
[avi @ 0x1c1b140] New audio stream 0:2 at pos:3241480 and DTS:1.3035s
frame=  750 fps=0.0 q=-1.0 Lsize=  105839kB time=00:00:30.00 bitrate=28901.0kbits/s
video:105469kB audio:313kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.053593%

$ ffmpeg -i segoyann.temp.avi

ffmpeg version N-72939-g5b0f55a Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --prefix=/home/gliksberg/bin/ffmpeg-build --enable-gpl --enable-nonfree --enable-pthreads --enable-libx264 --enable-libfaac --enable-libmp3lame
  libavutil      54. 27.100 / 54. 27.100
  libavcodec     56. 41.100 / 56. 41.100
  libavformat    56. 36.100 / 56. 36.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 17.100 /  5. 17.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.100 /  1.  2.100
  libpostproc    53.  3.100 / 53.  3.100
[avi @ 0x36fb3a0] non-interleaved AVI
[dvvideo @ 0x36fbdc0] AC EOB marker is absent pos=67
[dvvideo @ 0x36fbdc0] AC EOB marker is absent pos=69
Input #0, avi, from 'segoyann.temp.avi':
  Metadata:
    encoder         : Lavf56.36.100
  Duration: 00:00:30.04, start: 0.000000, bitrate: 28862 kb/s
    Stream #0:0: Video: dvvideo (dvsd / 0x64737664), yuv420p, 720x576 [SAR 16:15 DAR 4:3], 28800 kb/s, 25 fps, 25 tbr, 25 tbn, 25 tbc
    Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, s16p, 128 kb/s
At least one output file must be specified