D:\HDD DL\Tools\ffmpeg\bin>FOR /F "tokens=*" %G IN ('dir /d *.webm') DO ffmpeg -i "%G" -vf colorspace=itrc=smpte170m:all=bt709:iprimaries=bt709 -preset veryslow -crf 16 "%~nG.mp4"; done

outputs (for each of 226 videos):

D:\HDD DL\Tools\ffmpeg\bin>ffmpeg -i "60f15.webm" -vf colorspace=itrc=smpte170m:all=bt709:iprimaries=bt709 -preset veryslow -crf 16 "60f15.mp4"; done
ffmpeg version N-93554-gce92ee4b4f Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.2.1 (GCC) 20190212
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-amf --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt
  libavutil      56. 26.100 / 56. 26.100
  libavcodec     58. 48.101 / 58. 48.101
  libavformat    58. 27.100 / 58. 27.100
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 48.100 /  7. 48.100
  libswscale      5.  4.100 /  5.  4.100
  libswresample   3.  4.100 /  3.  4.100
  libpostproc    55.  4.100 / 55.  4.100
Input #0, matroska,webm, from '60f15.webm':
  Metadata:
    encoder         : Lavf56.40.101
  Duration: 00:00:02.75, start: 0.017000, bitrate: 8985 kb/s
    Stream #0:0: Video: vp8, yuv420p(progressive), 1280x720, SAR 1:1 DAR 16:9, 59.94 fps, 59.94 tbr, 1k tbn, 1k tbc (default)
[NULL @ 00000206ffe6de00] Unable to find a suitable output format for '60f15.mp4;'
60f15.mp4;: Invalid argument