FFmpeg reduz a duração do vídeo durante a transcodificação

Ao usar o ffmpeg no linux, meu vídeo de 4,3 GB e 2,21 segundos está sendo reduzido para 1,56 de duração. Estou tentando reduzir o tamanho do arquivo, mas não perder quadros.

steve@steve-OptiPlex-170L:~/Desktop$ ffmpeg -i microbe.avi microbe.mp4
ffmpeg version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Jun 12 2012 16:37:58 with gcc 4.6.3
*** THIS PROGRAM IS DEPRECATED ***
This program is only provided for compatibility and will be removed in a future release. Please use avconv instead.
Input #0, avi, from 'microbe.avi':
  Duration: 00:02:21.80, start: 0.000000, bitrate: 242311 kb/s
    Stream #0.0: Video: rawvideo, bgr24, 1280x960, 10 tbr, 10 tbn, 10 tbc
Incompatible pixel format 'bgr24' for codec 'mpeg4', auto-selecting format 'yuv420p'
[buffer @ 0x9f861e0] w:1280 h:960 pixfmt:bgr24
[avsink @ 0x9f86440] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out'
[scale @ 0x9f7d800] w:1280 h:960 fmt:bgr24 -> w:1280 h:960 fmt:yuv420p flags:0x4
Output #0, mp4, to 'microbe.mp4':
  Metadata:
    encoder         : Lavf53.21.0
    Stream #0.0: Video: mpeg4, yuv420p, 1280x960, q=2-31, 200 kb/s, 10 tbn, 10 tbc
Stream mapping:
  Stream #0.0 -> #0.0
Press ctrl-c to stop encoding
frame= 1164 fps=  6 q=31.0 Lsize=    3775kB time=116.40 bitrate= 265.7kbits/s    
video:3765kB audio:0kB global headers:0kB muxing overhead 0.272870%
steve@steve-OptiPlex-170L:~/Desktop$