self.app = Subprocess(['ffmpeg', '-y', '-i', '-', '-c:v', 'libx264', '-preset', 'veryfast', '-tune', 'zerolatency', '-f', 'flv', '-an', 'local-test-file.flv'], stdout=Subprocess.STREAM, stdin=Subprocess.STREAM)

Log:


ffmpeg version 3.2.5-1~bpo8+1 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 4.9.2 (Debian 4.9.2-10)
  configuration: --prefix=/usr --extra-version='1~bpo8+1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --disable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  libavutil      55. 34.101 / 55. 34.101
  libavcodec     57. 64.101 / 57. 64.101
  libavformat    57. 56.101 / 57. 56.101
  libavdevice    57.  1.100 / 57.  1.100
  libavfilter     6. 65.100 /  6. 65.100
  libavresample   3.  1.  0 /  3.  1.  0
  libswscale      4.  2.100 /  4.  2.100
  libswresample   2.  3.100 /  2.  3.100
  libpostproc    54.  1.100 / 54.  1.100
Input #0, matroska,webm, from 'pipe:':
  Metadata:
    encoder         : Chrome
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0(eng): Audio: opus, 48000 Hz, mono, fltp (default)
    Stream #0:1(eng): Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 1k tbr, 1k tbn, 1k tbc (default)
    Metadata:
      alpha_mode      : 1
[libx264 @ 0x55bcfa4ca540] using SAR=1/1
[libx264 @ 0x55bcfa4ca540] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX XOP FMA4 FMA3 LZCNT BMI1
[libx264 @ 0x55bcfa4ca540] profile High, level 5.2
[libx264 @ 0x55bcfa4ca540] 264 - core 142 r2431 a5831aa - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=1 ref=1 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=2 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=6 lookahead_threads=6 sliced_threads=1 slices=6 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=1 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, flv, to 'local-test-file.flv':
  Metadata:
    encoder         : Lavf57.56.101
    Stream #0:0(eng): Video: h264 (libx264) ([7][0][0][0] / 0x0007), yuv420p, 640x480 [SAR 1:1 DAR 4:3], q=-1--1, 1k fps, 1k tbn, 1k tbc (default)
    Metadata:
      alpha_mode      : 1
      encoder         : Lavc57.64.101 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream mapping:
  Stream #0:1 -> #0:0 (vp8 (native) -> h264 (libx264))
frame=   21 fps=7.0 q=30.0 size=      78kB time=00:00:02.88 bitrate= 222.4kbits/frame=   21 fps=3.5 q=30.0 size=      78kB time=00:00:02.88 bitrate= 222.4kbits/frame=   21 fps=2.3 q=30.0 size=      78kB time=00:00:02.88 bitrate= 222.4kbits/frame=   21 fps=1.7 q=30.0 size=      78kB time=00:00:02.88 bitrate= 222.4kbits/frame=   21 fps=1.4 q=30.0 size=      78kB time=00:00:02.88 bitrate= 222.4kbits/frame=   22 fps=1.2 q=30.0 size=      81kB time=00:00:02.88 bitrate= 228.4kbits/frame=   22 fps=1.0 q=30.0 size=      81kB time=00:00:02.88 bitrate= 228.4kbits/Past duration 0.999992 too large