$ ./ffmpeg -i TEST.AVI -c copy -f image2pipe - | ./ffmpeg -f image2pipe -framerate 10 -i - -c copy OUT.mp4
ffmpeg version 3.4.2-tessus Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzmq --enable-libzvbi --enable-version3 --pkg-config-flags=--static --disable-ffplay
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
ffmpeg version 3.4.2-tessus Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libass --enable-libbluray --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopus --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzmq --enable-libzvbi --enable-version3 --pkg-config-flags=--static --disable-ffplay
  libavutil      55. 78.100 / 55. 78.100
  libavcodec     57.107.100 / 57.107.100
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57. 10.100 / 57. 10.100
  libavfilter     6.107.100 /  6.107.100
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Input #0, avi, from 'TEST.AVI':
  Metadata:
    encoder         : Lavf57.56.101
  Duration: 00:16:40.00, start: 0.000000, bitrate: 605 kb/s
    Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj420p(pc, bt470bg/unknown/unknown), 1280x720, 605 kb/s, 1 fps, 1 tbr, 1 tbn, 1 tbc
Output #0, image2pipe, to 'pipe:':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: mjpeg (MJPG / 0x47504A4D), yuvj420p(pc, bt470bg/unknown/unknown), 1280x720, q=2-31, 605 kb/s, 1 fps, 1 tbr, 1 tbn, 1 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press [q] to stop, [?] for help
Input #0, image2pipe, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 1280x720, 10 fps, 10 tbr, 10 tbn, 10 tbc
Output #0, mp4, to 'OUT.mp4':
  Metadata:
    encoder         : Lavf57.83.100
    Stream #0:0: Video: mjpeg (mp4v / 0x7634706D), yuvj420p(pc, bt470bg/unknown/unknown), 1280x720, q=2-31, 10 fps, 10 tbr, 10240 tbn, 10 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
frame= 1000 fps=0.0 q=-1.0 Lsize=   73857kB time=00:16:40.00 bitrate= 605.0kbits/s speed=1.11e+03x
video:73857kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.000000%
frame=  286 fps=0.0 q=-1.0 Lsize=   73860kB time=00:00:28.50 bitrate=21230.1kbits/s speed=32.5x
video:73857kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.003603%