ffmpeg -i Firefly_-_EP05_-_Safe.vob.mp4 -ss 400 -t 30 -acodec copy -vcodec copy sample.mp4
FFmpeg version SVN-r6399, Copyright (c) 2000-2004 Fabrice Bellard
  configuration:  --prefix=/opt/local --prefix=/opt/local --disable-vhook --mandir=/opt/local/share/man --extra-cflags=-DHAVE_LRINTF --extra-ldflags=-d -L/opt/local/lib --enable-gpl --enable-mp3lame --enable-faac --enable-xvid --enable-a52 
  libavutil version: 49.0.1
  libavcodec version: 51.16.0
  libavformat version: 50.5.0
  built on Apr 21 2007 14:10:17, gcc: 4.0.0 (Apple Computer, Inc. build 5026)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Firefly_-_EP05_-_Safe.vob.mp4':
  Duration: 00:41:02.2, start: 0.000000, bitrate: 1028 kb/s
  Stream #0.0(und): Video: h264, yuv420p, 512x288, 25.00 fps(r)
  Stream #0.1(und): Audio: mp4a / 0x6134706D, 48000 Hz, stereo
File 'sample.mp4' already exists. Overwrite ? [y/N] y
Output #0, mp4, to 'sample.mp4':
  Stream #0.0: Video: avc1 / 0x31637661, yuv420p, 512x288, q=2-31, 25.00 fps(c)
  Stream #0.1: Audio: aac, 48000 Hz, stereo
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
[mp4 @ 0x2c3ba0]track 1: sample duration is not set
Could not write header for output file #0 (incorrect codec parameters ?)