C:\Users\enter.name.here\Desktop\mark>ffmpeg -f concat -i help.txt -c copy out.mkv
ffmpeg version N-63843-g6d40849 Copyright (c) 2000-2014 the FFmpeg developers
  built on Jun  8 2014 22:02:04 with gcc 4.8.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-
libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsox
r --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx
--enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-decklink --enable-zlib
  libavutil      52. 89.100 / 52. 89.100
  libavcodec     55. 66.100 / 55. 66.100
  libavformat    55. 42.101 / 55. 42.101
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  6.100 /  4.  6.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 19.100 /  0. 19.100
  libpostproc    52.  3.100 / 52.  3.100
Input #0, concat, from 'help.txt':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuv420p, 640x352, SAR 1:1 DAR 20:11, 25 fps, 25 tbr, 20k tbn, 50 tbc
Output #0, matroska, to 'out.mkv':
  Metadata:
    encoder         : Lavf55.42.101
    Stream #0:0: Video: h264 (H264 / 0x34363248), yuv420p, 640x352 [SAR 1:1 DAR 20:11], q=2-31, 25 fps, 1k tbn, 20k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
DTS -184467432147152928, next:320000 st:0 invalid dropping
PTS -184467432147152928, next:320000 invalid dropping st:0
[matroska @ 0459adc0] Can't write packet with unknown timestamp
av_interleaved_write_frame(): Invalid argument
frame=   11 fps=0.0 q=-1.0 Lsize=      29kB time=00:00:00.32 bitrate= 752.6kbits/s
video:37kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Conversion failed!