user@machine ~/Desktop $ avconv -i image.jpg -i audio.mp3 -c:v libx264 -crf 23 -c:a copy video.mpeg
avconv version 0.8.4-4:0.8.4-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Nov  6 2012 16:50:25 with gcc 4.6.3
Input #0, image2, from 'image.jpg':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: mjpeg, yuvj420p, 771x285 [PAR 300:300 DAR 257:95], 25 tbr, 25 tbn, 25 tbc
[mp3 @ 0x898f680] Format detected only with low score of 25, misdetection possible!
[mp3 @ 0x898f680] Could not find codec parameters (Audio: mp3, 0 channels, s16)
[mp3 @ 0x898f680] Estimating duration from bitrate, this may be inaccurate
audio.mp3: could not find codec parameters