Current version of ffmpeg produce twice longer output (in time terms) if
source file is non-interleaved AVI.

For example:

[root@diva-proxy ffmpeg-r19698]# ./ffmpeg_g -i /home/diva/2/TEST3-non-inter.avi -y /home/diva/2/TEST3-non-inter.mp4
FFmpeg version SVN-r19698, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  configuration: --prefix=/home/enctools --enable-libfaac --enable-libfaad --enable-libmp3lame --enable-postproc --enable-pthreads --enable-libx264 --enable-libxvid --extra-cflags=-I/home/enctools/include --extra-ldflags=-L/home/enctools/lib --enable-shared --enable-gpl --enable-nonfree --enable-avfilter --enable-avfilter-lavf
  libavutil     50. 3. 0 / 50. 3. 0
  libavcodec    52.32. 0 / 52.32. 0
  libavformat   52.38. 0 / 52.38. 0
  libavdevice   52. 2. 0 / 52. 2. 0
  libavfilter    0. 5. 0 /  0. 5. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Aug 25 2009 19:20:06, gcc: 4.3.2 20081105 (Red Hat 4.3.2-7)
[avi @ 0x8091420]non-interleaved AVI
Input #0, avi, from '/home/diva/2/TEST3-non-inter.avi':
  Duration: 00:00:01.92, start: 0.000000, bitrate: 31505 kb/s
    Stream #0.0: Video: dvvideo, yuv420p, 720x576, 25 tbr, 25 tbn, 25 tbc
    Stream #0.1: Audio: pcm_s16le, 48000 Hz, 2 channels, s16, 1536 kb/s
Output #0, mp4, to '/home/diva/2/TEST3-non-inter.mp4':
    Stream #0.0: Video: mpeg4, yuv420p, 720x576, q=2-31, 200 kb/s, 25 tbn, 25 tbc
    Stream #0.1: Audio: aac, 48000 Hz, 2 channels, s16, 64 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
frame=   85 fps=  0 q=24.8 Lsize=     351kB time=1.77 bitrate=1621.7kbits/s    
video:330kB audio:18kB global headers:0kB muxing overhead 0.719196%

As seen output has 85 frames but input is only 48 frames length.