Converting from .mkv to .mp4, having subtitle issues

[Blue Bomber]

I wish to edit an anime video in Sony Vegas so I converted it from .mkv to .mp4 using Bigasoft MKV Converter, the audio and video turned out fine but for some reason the program did not pick up on the subtitles and I cant seem to find an option to change that.

To fix this I used MKVExtract to extract the subtitles and then add them afterward (there is an option in Bigasoft to import from a subtitles file) yet when I add them it doesn't keep the same formatting as the subtitles originally had. It defaults to a different font, doesn't pick up on color changes and worst of all if a line of text is too long it just cuts it off instead of adding a second line underneath.

So basically what I'm asking, is there a good video converter that will convert from .mkv to .mp4 (or any other file type that Sony Vegas accepts) whilst keeping the subtitles correctly formatted? Alternatively, is there a way I can add subtitles to an .mp4 file and keep the formatting?

Thanks for your time.

[Baldrick]

What kind of subtitles? Ass/ssa ? Most converters can't hardcode subs/convert and keep the subtitle settings. avidemux supports ass subtitles but it's not that simple and crashes now and then.

[Blue Bomber]

The subtitles are .ass type. I'll try avidemux.