drawtext

ffmpeg -i sample.mov -c:v libvpx-vp9 -pix_fmt yuv420p -vf "drawtext=fontfile=C:\\Windows\\Fonts\\Arial\\arial.ttf:fontcolor=Yellow:box=1:boxcolor=black:fontsize=20:text='preview'" -pass 1 -b:v 700k -crf 10 -threads 16 -speed 4 -deadline good -cpu-used -8 -tile-columns 6 -frame-parallel 1 -an -f webm output_test.webm
ffmpeg version N-79075-ga7b8a6e Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmfx --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-decklink --enable-zlib
  libavutil      55. 19.100 / 55. 19.100
  libavcodec     57. 28.103 / 57. 28.103
  libavformat    57. 28.102 / 57. 28.102
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 39.102 /  6. 39.102
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Guessed Channel Layout for  Input Stream #0.1 : stereo
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'sample.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 537199360
    compatible_brands: qt
    creation_time   : 2016-02-17 01:22:24
    com.apple.finalcutstudio.media.uuid: C562639B-D02B-459D-B5A4-D13ABE427644
  Duration: 02:19:16.56, start: 0.000000, bitrate: 142000 kb/s
    Stream #0:0(eng): Video: prores (apcn / 0x6E637061), yuv422p10le(bt709), 1920x1080, 140437 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 2997 tbn, 2997 tbc (default)
    Metadata:
      creation_time   : 2016-02-17 01:22:24
      handler_name    : Apple Alias Data Handler
      encoder         : Apple ProRes 422
      timecode        : 01:00:00:00
    Stream #0:1(eng): Audio: pcm_s16le (sowt / 0x74776F73), 48000 Hz, 2 channels, s16, 1536 kb/s (default)
    Metadata:
      creation_time   : 2016-02-17 01:22:24
      handler_name    : Apple Alias Data Handler
    Stream #0:2(eng): Data: none (tmcd / 0x64636D74) (default)
    Metadata:
      creation_time   : 2016-02-17 06:02:37
      handler_name    : Apple Alias Data Handler
      timecode        : 01:00:00:00
File 'output_test.webm' already exists. Overwrite ? [y/N] y
Fontconfig error: Cannot load default config file
[Parsed_drawtext_0 @ 0000028bae46db20] impossible to init fontconfig
[AVFilterGraph @ 0000028bafa678a0] Error initializing filter 'drawtext' with args 'fontfile=C:\Windows\Fonts\Arial\arial.ttf:fontcolor=Yellow:box=1:boxcolor=black:fontsize=20:text=preview'
Error opening filters!