Why doesn't ffmpeg output a frame at 100% of the video's duration?

Question

fmpeg

Hello!
On some videos everything works fine, on some ffmpeg answers:

Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Output information about the file:

ffmpeg version 2.6 Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
  configuration: --prefix=/usr/local --enable-swscale --enable-avfilter --enable-avresample --enable-libmp3lame --enable-libvorbis --enable-libopus --enable-libtheora --enable-libschroedinger --enable-libopenjpeg --enable-libmodplug --enable-libvpx --enable-libspeex --enable-libass --enable-libbluray --enable-lzma --enable-gnutls --enable-fontconfig --enable-libfreetype --enable-libfribidi --disable-indev=jack --disable-outdev=xv --mandir=/usr/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/clang --enable-vda --arch=x86_64 --enable-yasm --enable-gpl --enable-postproc --enable-libx264 --enable-libxvid
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/work/1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    date            : 2015-01-15T14:25:18-05:00
    encoder         : Lavf56.25.101
  Duration: 00:00:30.04, start: 0.000000, bitrate: 475 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x368 [SAR 8:9 DAR 40:23], 328 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 138 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

The command to "pull" a frame from the video (it was necessary for 100% of the file time):

ffmpeg -y -i /work/1.mp4 -ss 00:00:30 -s 600x306 -vframes 1 -f image2 -aspect 1.9607843137254901   /work/1..jpg

ffmpeg output:

0150313-38884-17049tz.jpg
ffmpeg version 2.6 Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
  configuration: --prefix=/usr/local --enable-swscale --enable-avfilter --enable-avresample --enable-libmp3lame --enable-libvorbis --enable-libopus --enable-libtheora --enable-libschroedinger --enable-libopenjpeg --enable-libmodplug --enable-libvpx --enable-libspeex --enable-libass --enable-libbluray --enable-lzma --enable-gnutls --enable-fontconfig --enable-libfreetype --enable-libfribidi --disable-indev=jack --disable-outdev=xv --mandir=/usr/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/clang --enable-vda --arch=x86_64 --enable-yasm --enable-gpl --enable-postproc --enable-libx264 --enable-libxvid
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 26.100 / 56. 26.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 11.102 /  5. 11.102
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/work/1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    date            : 2015-01-15T14:25:18-05:00
    encoder         : Lavf56.25.101
  Duration: 00:00:30.04, start: 0.000000, bitrate: 475 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x368 [SAR 8:9 DAR 40:23], 328 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 138 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
[libx264 @ 0x7fa21b01c200] using SAR=1/1
[libx264 @ 0x7fa21b01c200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX AVX2 FMA3 LZCNT BMI2
[libx264 @ 0x7fa21b01c200] profile High, level 3.0
Output #0, image2, to '/work/1.jpg':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    date            : 2015-01-15T14:25:18-05:00
    encoder         : Lavf56.25.101
    Stream #0:0(und): Video: h264 (libx264), yuv420p, 600x306 [SAR 1:1 DAR 100:51], q=-1--1, 29.97 fps, 29.97 tbn, 29.97 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      encoder         : Lavc56.26.100 libx264
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
frame=    0 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.00 bitrate=N/A
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Thanks in advance!