mencoder

mencoder -ovc copy -oac copy -ss 00:00:03 -endpos 00:00:50 -o ~/out.mp4 ~/in.mp4
mencoder -ovc copy -oac pcm -ss 00:00:03 -endpos 00:00:50 -o ~/out.mp4 ~/in.mp4
mencoder -ovc copy -oac lavc -ss 00:00:03 -endpos 00:00:50 -o ~/out.mp4 ~/in.mp4
mencoder -ovc copy -oac mp3lame -ss 00:00:03 -endpos 00:00:50 -o ~/out.mp4 ~/in.mp4
mencoder -ovc copy -oac mp3lame -lameopts vbr=2:q=3 -ss 00:00:03 -endpos 00:00:50 -o ~/out.mp4 ~/in.mp4

mencoder -ovc copy -oac copy -o ~/12.avi ~/1.avi ~/2.avi

mencoder -oac help
Available codecs:
   copy     - frame copy, without re-encoding (useful for AC3)
   pcm      - uncompressed PCM audio
   mp3lame  - cbr/abr/vbr MP3 using libmp3lame
   lavc     - FFmpeg audio encoder (MP2, AC3, ...)

mencoder -ovc help
Available codecs:
   copy     - frame copy, without re-encoding. Doesn't work with filters.
   frameno  - special audio-only file for 3-pass encoding, see DOCS.
   raw      - uncompressed video. Use fourcc option to set format explicitly.
   nuv      - nuppel video
   lavc     - libavcodec codecs - best quality!
   vfw      - VfW DLLs, read DOCS/HTML/en/encoding-guide.html.
   qtvideo  - QuickTime DLLs, currently only SVQ1/3 are supported.
   xvid     - XviD encoding
   x264     - H.264 encoding