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)
• Noto Sans Thai

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.

Past comments

The comment API returns only the recent comments of a video. When these comments are fewer than comments, the plugin loads older comments until it has at least that many comments for each language, or until no older comments are left. comments=all loads all past comments.

Fetching past comments requires a free Niconico account. Pass your cookies to yt-dlp, for example with --cookies-from-browser:

yt-dlp --cookies-from-browser chrome --embed-subs \
  --use-postprocessor "NicoComments:when=video;comments=10000" \
  https://www.nicovideo.jp/watch/sm9

Smooth scrolling in mpv

mpv redraws subtitles only when the video frame changes. To update them at the display refresh rate, load the mpv script nicocomments-display-fps.lua. The script converts the video to the refresh rate of the display that shows the mpv window.

The script adds an fps video filter. If mpv or IINA saves the playback position, it also saves this filter, and the filter stays in effect when you resume the video without the script.

mpv

Download the script and run mpv with it:

mpv --script=/path/to/nicocomments-display-fps.lua --video-sync=display-resample video.mkv

nicocomments-play.sh runs the same command and passes its arguments to mpv. Put it in the same directory as nicocomments-display-fps.lua:

chmod +x nicocomments-play.sh
./nicocomments-play.sh video.mkv

On Windows, use nicocomments-play.bat in the same way:

nicocomments-play.bat video.mkv

To use the script for all videos, put it in the mpv scripts directory and add video-sync=display-resample to mpv.conf:

IINA

IINA plays videos with mpv, so it can use the same script. Open Settings > Advanced, select Enable advanced settings, and add these entries to Additional mpv options:

If you already set up the mpv scripts directory and mpv.conf, you can instead select Use config directory and choose ~/.config/mpv. Restart IINA after you change these settings.

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.