also,
i've found an mpeg2 stream with display_size set in the sequence_display_extension.
it seems to be set for pan and scan (horizontal_display_size=540).
this throws off ffmpeg on it's par/dar calculations though.
and it shouldn't.
it detects a 2.35 dar in this case, seemingly disregarding
the letterboxing.

so you get borked playback with say VLC,
and attempting to convert with ffmpeg maintaining par/dar,
junk like this:

ffmpeg -i mpeg2-sequence-display-ext.m2v -an out.mp4
FFmpeg version SVN-r12888, Copyright (c) 2000-2008 Fabrice Bellard, et al.
  configuration: --enable-memalign-hack --enable-gpl --enable-libx264
  libavutil version: 49.6.0
  libavcodec version: 51.55.0
  libavformat version: 52.13.0
  libavdevice version: 52.0.0
  built on Apr 18 2008 20:01:26, gcc: 4.2.3 (TDM-1 for MinGW)
Input #0, mpegvideo, from 'mpeg2-sequence-display-ext.m2v':
  Duration: 00:00:09.48, bitrate: 7200 kb/s
    Stream #0.0: Video: mpeg2video, yuv420p, 720x576 [PAR 256:135 DAR 64:27], 72
00 kb/s, 25.00 tb(r)
Output #0, mp4, to 'out.mp4':
    Stream #0.0: Video: mpeg4, yuv420p, 720x576 [PAR 201:106 DAR 1005:424], q=2-
31, 200 kb/s, 25.00 tb(c)
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding
frame=  235 fps= 63 q=31.0 Lsize=     816kB time=9.4 bitrate= 711.3kbits/s
video:814kB audio:0kB global headers:0kB muxing overhead 0.313515%