ffmpeg -i in.mkv -vcodec copy -r ntsc-film -acodec copy out.mp4
FFmpeg version SVN-r19654, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  configuration: --prefix=/opt/local --enable-nonfree --enable-gpl --enable-postproc --enable-avfilter --enable-avfilter-lavf --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libdirac --enable-libschroedinger --enable-libfaac --enable-libfaad --enable-libxvid --enable-libx264 --mandir=/opt/local/share/man --enable-shared --enable-pthreads --disable-indevs --cc=gcc-4.0
  libavutil     50. 3. 0 / 50. 3. 0
  libavcodec    52.32. 0 / 52.32. 0
  libavformat   52.37. 0 / 52.37. 0
  libavdevice   52. 2. 0 / 52. 2. 0
  libavfilter    1. 5. 0 /  1. 5. 0
  libswscale     1. 7. 1 /  1. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Aug 20 2009 12:07:09, gcc: 4.0.1 (Apple Inc. build 5493)

Seems stream 2 codec frame rate differs from container frame rate: 47.95 (48000/1001) -> 23.98 (24000/1001)
Input #0, matroska, from 'in.mkv':
  Duration: 01:36:44.04, start: 0.000000, bitrate: N/A
    Stream #0.0: Audio: ac3, 48000 Hz, 2 channels, s16
    Stream #0.1(spa): Subtitle: 0x0000
    Stream #0.2(eng): Video: h264, yuv420p, 1920x1080, PAR 1:1 DAR 16:9, 23.98 tbr, 1k tbn, 47.95 tbc
    Stream #0.3(eng): Audio: dca, 48000 Hz, 6 channels, s16
    Stream #0.4(eng): Subtitle: 0x0000
[mp4 @ 0x1902e00]track 1: codec frame size is not set
Output #0, mp4, to 'out.mp4':
    Stream #0.0(eng): Video: libx264, yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], q=2-31, 1k tbn, 1k tbc
    Stream #0.1: Audio: ac3, 48000 Hz, 2 channels, s16
Stream mapping:
  Stream #0.2 -> #0.0
  Stream #0.0 -> #0.1
Could not write header for output file #0 (incorrect codec parameters ?)