Does the resulting .m4v have audio? If not, what audio codec does the .mts file use? Can you play the .mts in VLC Player and hear audio?
Yes. I loaded to codecs you mentioned earlier as well. It's working now, though I'm not sure why. A friend of mine gave me his External HDD to make a video and he just copied the files that are the .mts files. It seems there are 2 of each kind that it saves, one with audio and one without, but the one I convert that doesn't have audio after conversion has audio when played in VLC. This is my first experience with MTS. I appreciate your post. Hopefully, I'll be able to get the videos converted properly!