e@Linux1 ~/Videos $ ffmpeg -i Anastasia.mkv -aspect 16:9 -b:v 1500k out.aviffmpeg version 0.8.1-4:0.8.1-0ubuntu1, Copyright (c) 2000-2011 the Libav developers
  built on Mar 22 2012 05:29:10 with gcc 4.6.3
This program is not developed anymore and is only provided for compatibility. Use avconv instead (see Changelog for the list of incompatible changes).
[matroska,webm @ 0x9920260] Estimating duration from bitrate, this may be inaccurate

Seems stream 0 codec frame rate differs from container frame rate: 47.95 (5000000/104271) -> 23.98 (24000/1001)
Input #0, matroska,webm, from 'Anastasia.mkv':
  Duration: 01:34:10.65, start: 0.000000, bitrate: 1536 kb/s
    Stream #0.0(eng): Video: h264 (High), yuv420p, 1280x544, PAR 1:1 DAR 40:17, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
    Stream #0.1(eng): Audio: dca (DTS), 48000 Hz, 5.1, s16, 1536 kb/s (default)
File 'out.avi' already exists. Overwrite ? [y/N] y
[buffer @ 0x99daf40] w:1280 h:544 pixfmt:yuv420p
Output #0, avi, to 'out.avi':
    Stream #0.0(eng): Video: mpeg4, yuv420p, 1280x544 [PAR 34:45 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 23.98 tbc
    Stream #0.1(eng): Audio: libmp3lame, 48000 Hz, 5.1, s16, 200 kb/s (default)
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Error while opening encoder for output stream #0.1 - maybe incorrect parameters such as bit_rate, rate, width or height
graeme@Linux1 ~/Videos $