yt-dlp-nicocomments

A yt-dlp postprocessor plugin that converts Niconico comments to an ASS subtitle track.

Fonts

The plugin lays out and draws comments with:

• Noto Sans JP (Regular and Bold)
• Noto Serif JP (Regular)
• Noto Emoji
• Noto Sans Math
• Noto Sans Symbols 2
• Noto Sans SC (Regular)
• Noto Sans KR (Regular)

The package includes these fonts under the SIL Open Font License 1.1. With --embed-subs, the plugin saves the video as an MKV file and attaches the fonts to it (unless embedfonts=false).

To keep the video file small, the plugin removes the unused glyphs from the fonts using fontTools.

Install

If yt-dlp is installed with uv or pip, install the plugin in the same environment:

uv tool install yt-dlp --with yt-dlp-nicocomments

pip install -U yt-dlp-nicocomments

If you use the yt-dlp executable, download the .whl file from the latest release and put it in a yt-dlp plugin directory:

To make sure that the release workflow of this repository built the file, run:

gh attestation verify yt_dlp_nicocomments-*.whl -R hiroki-io/yt-dlp-nicocomments

The yt-dlp executable cannot load fontTools from the plugin directory. To attach smaller fonts, install fontTools so that the pyftsubset command is on PATH, for example with brew install fonttools or pipx install fonttools.

To use the code from a clone of this repository, download the fonts and put the repository in a plugin directory:

python3 ~/yt-dlp-nicocomments/tools/font_data.py
mkdir -p ~/.config/yt-dlp/plugins
ln -s ~/yt-dlp-nicocomments ~/.config/yt-dlp/plugins/yt-dlp-nicocomments

Usage

yt-dlp --embed-subs --use-postprocessor "NicoComments:when=video" \
  https://www.nicovideo.jp/watch/sm9

when=video is necessary because the plugin must run before yt-dlp writes the subtitles.

Options

Options are passed after the postprocessor name (NicoComments:), separated by semicolons:

Example:

--use-postprocessor "NicoComments:when=video;lang=ja,en;nglevel=high"

Shortcut

To shorten the command, define an alias in the yt-dlp configuration file ~/.config/yt-dlp/config:

--alias --nico "--embed-subs --use-postprocessor NicoComments:when=video"

Then use the alias instead of the options:

yt-dlp --nico https://www.nicovideo.jp/watch/sm9

Save only the comment track

To save the comment track as an ASS file without the video, use --write-subs and --skip-download:

yt-dlp --skip-download --write-subs --use-postprocessor "NicoComments:when=video" \
  https://www.nicovideo.jp/watch/sm9

The ASS file does not contain the fonts, so install the font files linked in Fonts on the computer that plays it.

Burn the comments into the video

To burn the comment track into the video, run this command with an FFmpeg build that includes libass:

ffmpeg -i video.mkv -vf subtitles=video.mkv -c:a copy video-burned.mp4

FFmpeg encodes the video again, so this takes time and lowers the quality.