$ avconv -i old_video.avi -i new_sound.wav -vcodec copy -acodec copy -map 0:0 -map 1:0 new_video.avi
avconv version 0.8.16-6:0.8.16-1, Copyright (c) 2000-2014 the Libav developers
  built on Sep 16 2014 23:10:48 with gcc 4.7.2
[avi @ 0x13216c0] max_analyze_duration reached
Input #0, avi, from 'old_video.avi':
  Duration: 00:00:28.20, start: 0.000000, bitrate: 970 kb/s
    Stream #0.0: Video: Ipma / 0x616D7049, 180x195, 15 fps, 15 tbr, 15 tbn, 15 tbc
    Stream #0.1: Audio: pcm_u8, 22050 Hz, 1 channels, u8, 176 kb/s
[wav @ 0x13244a0] max_analyze_duration reached
Input #1, wav, from 'new_sound.wav':
  Duration: 00:00:28.20, bitrate: 176 kb/s
    Stream #1.0: Audio: pcm_u8, 22050 Hz, 1 channels, u8, 176 kb/s
File 'new_video.avi' already exists. Overwrite ? [y/N] y
Output #0, avi, to 'new_video.avi':
  Metadata:
    ISFT            : Lavf53.21.1
    Stream #0.0: Video: Ipma / 0x616D7049, 180x195, q=2-31, 15 tbn, 15 tbc
    Stream #0.1: Audio: pcm_u8, 22050 Hz, 1 channels, 176 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #1:0 -> #0:1 (copy)
Press ctrl-c to stop encoding
frame=  423 fps=  0 q=-1.0 Lsize=    2738kB time=28.20 bitrate= 795.4kbits/s
video:2107kB audio:607kB global headers:0kB muxing overhead 0.879129%