ffmpeg video will not play in browser

Question

I'm trying to create a simple video with an image and some audio using this command:

ffmpeg -loop 1 -framerate 2 -i image.jpg -i audio.mp3 -c:v libx264 -c:a aac -strict -2 -preset medium -tune stillimage -crf 0 -shortest -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" -pix_fmt yuv420p -movflags +faststart output.mp4

But the resulting video will not play in latest firefox, though it will play in chrome 63.

ffmpeg stats:

ffmpeg version 3.4.1-1+b1 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 7 (Debian 7.2.0-18)
  configuration: --prefix=/usr --extra-version=1+b1 --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 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --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-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  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
  libavresample   3.  7.  0 /  3.  7.  0
  libswscale      4.  8.100 /  4.  8.100
  libswresample   2.  9.100 /  2.  9.100
  libpostproc    54.  7.100 / 54.  7.100
Hyper fast Audio and Video encoder

Any ideas?

Answer 1

-crf of 0 will force the output profile to High 4:4:4 profile, which Firefox doesn't support. Set CRF to at least 1 .