[FFmpeg-user] ct a video precisly

[gagall at free.fr]

Hello,

I'm trying to cut a video to get 12s sequences. It needs to be accurate.
But when I ask a 12 seconds sequence (not from the begining for this example) , I get around 12:01 seconds.
The command line is :
ffmpeg -ss 00:00:00.00 -i GOPR0151.mp4 -b:v 30150 -t 00:00:12.00 -acodec copy -vcodec copy GOPR0151_002.mp4

and even, when I start from 00:02:12.00, the output lasts 12:33 seconds.

Can anybody tell me who to get more accuracy, please ?
I noticed that the bitrate is not the same in the orginal video than in the output. Is it important ?
Here are the informations of the original video :
ffprobe.exe GOPR0151.mp4
ffprobe version N-74751-gb54e03c Copyright (c) 2007-2015 the FFmpeg developers
  built with gcc 4.9.3 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnu
tls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enab
le-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable
-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --ena
ble-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --e
nable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
  libavutil      54. 31.100 / 54. 31.100
  libavcodec     56. 59.100 / 56. 59.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 40.100 /  5. 40.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'GOPR0151.mp4':
  Metadata:
    major_brand     : avc1
    minor_version   : 0
    compatible_brands: avc1isom
    creation_time   : 2014-10-25 09:19:36
  Duration: 00:17:24.30, start: 0.000000, bitrate: 30150 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1280x960 [SAR 1:1 DAR 4:3], 30002 kb/s, 100 fps, 100 tbr, 180k tbn,
 200 tbc (default)
    Metadata:
      creation_time   : 2014-10-25 09:19:36
      handler_name    :  GoPro AVC
      encoder         : GoPro AVC encoder
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      creation_time   : 2014-10-25 09:19:36
      handler_name    :  GoPro AAC


And the output :
ffprobe.exe GOPR0151_002.mp4
ffprobe version N-74751-gb54e03c Copyright (c) 2007-2015 the FFmpeg developers
  built with gcc 4.9.3 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnu
tls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enab
le-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable
-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --ena
ble-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --e
nable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
  libavutil      54. 31.100 / 54. 31.100
  libavcodec     56. 59.100 / 56. 59.100
  libavformat    56. 40.101 / 56. 40.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 40.100 /  5. 40.100
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  2.101 /  1.  2.101
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'GOPR0151_002.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf56.40.101
  Duration: 00:00:12.33, start: 0.309333, bitrate: 30273 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1280x960 [SAR 1:1 DAR 4:3], 30187 kb/s, 100 fps, 100 tbr, 180k tbn,
 200 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler


Thanks in advance

Fridu