merging

ffmpeg -i 01.mp4 -i 02.mp4 -map 0:a:0 -map 0:v:0 -c copy output.mp4

Output:

ffmpeg version 1.0 Copyright (c) 2000-2012 the FFmpeg developers
  built on Nov 13 2012 17:39:28 with Apple clang version 4.1 (tags/Apple/clang-421.11.65) (based on LLVM 3.1svn)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/1.0 --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --cc=cc --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid
  libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fda39006600] multiple edit list entries, a/v desync might occur, patch welcome
    Last message repeated 1 times
[dca @ 0x7fda39034400] Number of channels changed in DCA decoder (2 -> 6)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '01.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.29.104
  Duration: 00:07:48.31, start: 0.041000, bitrate: 37551 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 33110 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: dts (DTS-HD MA) (mp4a / 0x6134706D), 48000 Hz, 5.1(side), s16, 1536 kb/s
    Metadata:
      handler_name    : SoundHandler
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fda39018a00] multiple edit list entries, a/v desync might occur, patch welcome
    Last message repeated 1 times
[dca @ 0x7fda3901a000] Number of channels changed in DCA decoder (2 -> 6)
Input #1, mov,mp4,m4a,3gp,3g2,mj2, from '02.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.29.104
  Duration: 00:00:26.32, start: 0.041000, bitrate: 41304 kb/s
    Stream #1:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 36740 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
    Metadata:
      handler_name    : VideoHandler
    Stream #1:1(und): Audio: dts (DTS-HD MA) (mp4a / 0x6134706D), 48000 Hz, 5.1(side), s16, 1536 kb/s
    Metadata:
      handler_name    : SoundHandler
[mp4 @ 0x7fda390b8e00] track 0: codec frame size is not set
Output #0, mp4, to 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.29.104
    Stream #0:0(und): Audio: dts ([169][0][0][0] / 0x00A9), 48000 Hz, 5.1(side), 1536 kb/s
    Metadata:
      handler_name    : SoundHandler
    Stream #0:1(und): Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 33110 kb/s, 23.98 fps, 90k tbn, 90k tbc
    Metadata:
      handler_name    : VideoHandler
Stream mapping:
  Stream #0:1 -> #0:0 (copy)
  Stream #0:0 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame=11228 fps=1923 q=-1.0 Lsize= 2146714kB time=00:07:48.29 bitrate=37552.7kbits/s
video:1892812kB audio:253465kB subtitle:0 global headers:0kB muxing overhead 0.020381%