ffmpeg normalize command+output

PS D:\videos> ffmpeg -i webcam.mkv -pix_fmt yuv420p -s 1600x896 -crf 18 -preset ultrafast -b:a 128k -vf "normalize=smoothing=30:independence=0" webcam-420-normalized.mp4
ffmpeg version N-93871-g8cf947ca4c Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.3.1 (GCC) 20190414
  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. 28.100 / 56. 28.100
  libavcodec     58. 52.101 / 58. 52.101
  libavformat    58. 27.103 / 58. 27.103
  libavdevice    58.  7.100 / 58.  7.100
  libavfilter     7. 53.101 /  7. 53.101
  libswscale      5.  4.101 /  5.  4.101
  libswresample   3.  4.100 /  3.  4.100
  libpostproc    55.  4.100 / 55.  4.100
Input #0, matroska,webm, from 'webcam.mkv':
  Metadata:
    ENCODER         : Lavf58.27.103
  Duration: 00:01:00.15, start: 0.000000, bitrate: 24240 kb/s
    Stream #0:0: Video: ffv1 (FFV1 / 0x31564646), bgr0(progressive), 1600x896, 30 fps, 30 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      ENCODER         : Lavc58.52.101 ffv1
      DURATION        : 00:01:00.150000000
    Stream #0:1: Audio: flac, 44100 Hz, mono, s16 (default)
    Metadata:
      ENCODER         : Lavc58.52.101 flac
      DURATION        : 00:01:00.000000000
Stream mapping:
  Stream #0:0 -> #0:0 (ffv1 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (flac (native) -> aac (native))
Press [q] to stop, [?] for help
[libx264 @ 000002384b332900] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX XOP FMA3 BMI1
[libx264 @ 000002384b332900] profile Constrained Baseline, level 4.0, 4:2:0, 8-bit
[libx264 @ 000002384b332900] 264 - core 157 r2970 5493be8 - H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=18.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
Output #0, mp4, to 'webcam-420-normalized.mp4':
  Metadata:
    encoder         : Lavf58.27.103
    Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p(progressive), 1600x896, q=-1--1, 30 fps, 15360 tbn, 30 tbc (default)
    Metadata:
      DURATION        : 00:01:00.150000000
      encoder         : Lavc58.52.101 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1: Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp (16 bit), 128 kb/s (default)
    Metadata:
      DURATION        : 00:01:00.000000000
      encoder         : Lavc58.52.101 aac
[matroska,webm @ 000002384ae8a5c0] Element at 0xadd04ee ending at 0xadd0b0d exceeds containing master element ending at 0xadd04e8
frame= 1805 fps= 78 q=-1.0 Lsize=  125204kB time=00:01:00.13 bitrate=17056.6kbits/s dup=900 drop=0 speed=2.59x
video:124211kB audio:940kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.042031%
[libx264 @ 000002384b332900] frame I:8     Avg QP:11.88  size:209674
[libx264 @ 000002384b332900] frame P:1797  Avg QP:14.42  size: 69846
[libx264 @ 000002384b332900] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 000002384b332900] mb P  I16..4: 15.2%  0.0%  0.0%  P16..4: 41.8%  0.0%  0.0%  0.0%  0.0%    skip:43.1%
[libx264 @ 000002384b332900] coded y,uvDC,uvAC intra: 83.3% 74.8% 67.3% inter: 26.8% 37.4% 29.7%
[libx264 @ 000002384b332900] i16 v,h,dc,p: 35% 39% 22%  5%
[libx264 @ 000002384b332900] i8c dc,h,v,p: 35% 35% 25%  5%
[libx264 @ 000002384b332900] kb/s:16911.88
[aac @ 000002384b334600] Qavg: 139.988