Heavy artefact in the middle of the video

[Fak3]

Describe the bug 0.5.0 produces heavy artefacts in the middle of the video, as shown in the sample below.

To Reproduce Watch or download the encoded result here: https://drive.google.com/file/d/1kaQCIcGPAzmjIS-4zb8JsALle7o8hoa0/view?t=460 at timestamp 07:41 the picture starts to be very crippled by artefacts for ~3 seconds

This was produced from this h264 source video: link with the following command: ffmpeg -i dst.mp4 -c:v librav1e -b:v 100k -rav1e-params speed=5 -acodec copy rav12.mkv

Expected behavior No heavy artifacts should be present in the output

Version: 0.5.0 Operating system: Linux localhost.localdomain 5.14.6-1-default #1 SMP Mon Sep 20 07:02:13 UTC 2021 (6131a3c) x86_64 x86_64 x86_64 GNU/Linux

Console Output

$ ffmpeg -i dst.mp4 -c:v librav1e -b:v 100k -rav1e-params speed=5 -acodec copy rav12.mkv
ffmpeg version 4.4.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11 (SUSE Linux)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --incdir=/usr/include/ffmpeg --extra-cflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -ffat-lto-objects -g' --optflags='-O2 -Wall -D_FORTIFY_SOURCE=2 -fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -Werror=return-type -flto=auto -ffat-lto-objects -g' --disable-htmlpages --enable-pic --disable-stripping --enable-shared --disable-static --enable-gpl --enable-version3 --enable-libsmbclient --disable-openssl --enable-avresample --enable-gnutls --enable-ladspa --enable-vulkan --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcelt --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libdc1394 --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librav1e --enable-librubberband --enable-libsvtav1 --enable-libsoxr --enable-libspeex --enable-libssh --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libv4l2 --enable-libvpx --enable-libwebp --enable-libxml2 --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lto --enable-lv2 --enable-libmfx --enable-vaapi --enable-vdpau --enable-version3 --enable-libfdk-aac-dlopen --enable-nonfree --enable-libvo-amrwbenc --enable-libx264 --enable-libx265 --enable-librtmp --enable-libxvid
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'dst.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.83.100
  Duration: 00:15:20.10, start: 0.000000, bitrate: 278 kb/s
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 640x480, 242 kb/s, 15 fps, 50 tbr, 16k tbn, 30 tbc (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 16000 Hz, mono, fltp, 32 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> av1 (librav1e))
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
Output #0, matroska, to 'rav12.mkv':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.76.100
  Stream #0:0(und): Video: av1 (AV01 / 0x31305641), yuv420p(tv, bt709, progressive), 640x480, q=2-31, 100 kb/s, 15 fps, 1k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc58.134.100 librav1e
  Stream #0:1(und): Audio: aac (LC) ([255][0][0][0] / 0x00FF), 16000 Hz, mono, fltp, 32 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
frame=13798 fps=4.9 q=-0.0 Lsize=   15060kB time=00:15:20.06 bitrate= 134.1kbits/s speed=0.324x    
video:11259kB audio:3638kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.092567%

[tdaede]

Is this a regression? (is this problem new with 0.5.0?)

[Fak3]

Unfortunately I don't have older version around to check