I'm trying to burn .ass subtitles onto a .webm, using ffmpeg -i input.webm -vf ass=subtitles.ass output.webm but it shrinks from like 150MB to 9MB. How do I add the subtitles without losing quality ?


1 Answer 1



ffmpeg -i input.webm -vf ass=subtitles.ass -b:v 0 -crf 20 output.webm

The libvpx encoders for WebM, by default, perform Constrained Quality encoding, and use the bitrate as a ceiling. Default bitrate is 200 kbps. To remove bitrate ceiling, set bitrate to 0. -crf controls the quality level.

  • Cheers! Worked perfectly.
    – Jon
    Commented May 16, 2019 at 20:32
  • 2
    @Jon, so why you don't accept this answer? Click on check mark near it.
    – MarianD
    Commented May 16, 2019 at 21:06

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