i use Free online file converter
usually on my PC running Linux, but just tried it out w/ microb
(@#$%?&*! fennec doesn't allow access to /media/mmc1... mozilla more & more starts to function like m@ke$$h!t )
works perfectly.
plus it allows to select intervals (00:00:00 / hh:mm:ss)
top of the blues, if you do the conversion from a PC, it provides a QR-code & allows it to be downloaded a few times (from the phone, directly, thus not having to "upload" it )

PS: honestly, i have lost count of how many programs i could (and partly have) install(-ed) on my PC that would (nearly!) do the same as this nifty site...