I'm trying to make webms with ffmpeg from my anime but I keep getting this:

[webm @ 000002431260fac0] Only VP8 or VP9 or AV1 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM.
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument

can someone just write the command I need to use to make a webm? for example say the file is anime.mkv and I want to make a webm that starts from 18:15 to 19:45 (minutes:seconds). I don't need audio. I would like to keep subtitles. I tried googling but all the examples don't work for me I keep getting that same error...