MKV, subtitles are tiny. How to change font size?

[anarchyx34]

I've got a MKV file with subtitles that I'm trying to convert to AVI. I'm using FFMPEGX, and I select 'burn subtitle', but they come out too small. Tried changing the font size and it makes no difference. Come to think of it, when playing the video in VLC the subs are small there as well. Could it be that the subtitles in this MKV are image and not text based and that's why the size wont change?

[Ai Haibara]

Use the Mac version of MediaInfo, and see what format it lists for the subtitle stream(s) in the MKV. (I don't know if VLC's file information feature will work for that, but give it a try as well.)