stdin

$ curl http://simg3.gelbooru.com/samples/2e/c7/sample_2ec7e586f79ac94f9c22a855fcae1d20.jpg | ffmpeg -f image2pipe -i -
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0ffmpeg version N-70730-ge802abd Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.54) (based on LLVM 3.5svn)
  configuration: --extra-cflags='-march=native' --disable-optimizations --disable-stripping --enable-debug --enable-libx265 --enable-gpl --enable-libopus --enable-version3 --enable-nonfree --enable-postproc --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-gnutls --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --prefix=/usr/local --enable-static --enable-shared --enable-avresample --enable-vda --enable-opencl --enable-libzvbi --cc=clang
  libavutil      54. 20.100 / 54. 20.100
  libavcodec     56. 28.100 / 56. 28.100
  libavformat    56. 25.101 / 56. 25.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 12.100 /  5. 12.100
  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
[image2pipe @ 0x7ff3f180da00] Could not find codec parameters for stream 0 (Video: none, none): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' options
pipe:: could not find codec parameters
Input #0, image2pipe, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: none, none, 25 tbr, 25 tbn, 25 tbc
At least one output file must be specified
 13  370k   13 50338    0     0  90525      0  0:00:04 --:--:--  0:00:04   98k
curl: (23) Failed writing body (0 != 8448)