FFmpegStatus.js

const isNewFFmpegProcess = input => RegExp('^ffmpeg version', 'g').test(input)
const isWarning = input => RegExp('Configuration of video device failed, falling back to default', 'g').test(input)
const isInput = input => RegExp('^Input #', 'g').test(input)
const isStreamMapping = input => RegExp('^Stream mapping', 'g').test(input)
const isOutput = input => RegExp('^Output #', 'g').test(input)
const isFrame = input => RegExp('^frame=', 'g').test(input)
const isSize = input => RegExp('^size=', 'g').test(input)

const match = (expression, input) => RegExp(expression, 'g').exec(input).slice(1).map(x => x.trim())

const sizes = { b: 1, kb: 1024, mb: 1024 * 1024, gb: 1024 * 1024 * 1024 }
const toBytes = size => parseInt(size) * sizes[size.substr(-2).toLowerCase()]
const toBits = bitRate => Math.round(parseFloat(bitRate) * sizes[bitRate.substr(-7, 2)])

const toMS = time => time.split(':').map((t, i) => t * (60 ** (2 - i) )).reduce((a, b) => a + b, 0) * 1000

const extractFrame = input => {
    const query = 'frame=(.*?)fps=(.*?)q=(.*?)size=(.*?)time=(.*?)bitrate=(.*?)dup=(.*?)drop=(.*?)speed=(.*?)x'
    const [frame, fps, q, size, time, bitRate, dup, drop, speed] = match(query, input)
    return {
        frame: parseInt(frame),
        // fps: parseFloat(fps),
        // quality: parseFloat(q),
        size: toBytes(size),
        time: toMS(time),
        bitRate: toBits(bitRate), //bits
         // dup: parseInt(dup),
        drop: parseInt(drop),
        speed: parseFloat(speed)
    }
}

const extractSize = input => {
    const [size, time, bitRate, speed] = match('size=(.*?)time=(.*?)bitrate=(.*?)speed=(.*?)x', input)
    return {
        size: toBytes(size), //bytes
        time: toMS(time), //ms
        bitRate: toBits(bitRate), //bits
        speed: parseFloat(speed)
    }
}


const lines = [`ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.27)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_4 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100`,
      `[AVFoundation indev @ 0x7f986ec04640] Configuration of video device failed, falling back to default.`,
      `Input #0, avfoundation, from '1:':
  Duration: N/A, start: 114417.535333, bitrate: N/A
    Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 3840x2160, 30 tbr, 1000k tbn, 1000k tbc`,
      `Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> hevc (hevc_videotoolbox))
Press [q] to stop, [?] for help`,
   `Output #0, hevc, to 'pipe:1':
  Metadata:
    encoder         : Lavf58.45.100
    Stream #0:0: Video: hevc (hevc_videotoolbox), yuv420p, 1280x720, q=2-31, 1000 kb/s, 30 fps, 30 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.91.100 hevc_videotoolbox`,
    `frame=   18 fps=0.0 q=-0.0 size=     308kB time=00:00:00.43 bitrate=5828.2kbits/s dup=4 drop=0 speed=0.848x    `,
    `size=       0kB time=00:00:00.48 bitrate=   2.3kbits/s speed=0.967x    `
]

for (const line of lines) {
    if(isFrame(line)) {
        console.log(extractFrame(line))
    } else if(isSize(line)) {
        console.log(extractSize(line))
    } else if(isNewFFmpegProcess(line) || isWarning(line) || isInput(line) || isOutput(line) || isStreamMapping(line)) {
        console.log('Loading ...')
    } else throw new Error(line)
}

Similar work here and here