convert avi w/ srt to mp4 video?

I don't know what .srt is, so no guarantees here, but Handbrake is the best free video converter I know of.

http://handbrake.fr/

Take a look at mpeg streamclip from Squared 5 - it's free.

Handbrake does have an audio and subtitles function. Again, I don't know your format but it's worth looking at.

It's important that your srt files are in the same folder as the avi or quicktime file. Make a new folder and place the movie file along with the srt file. That way the movie file can find it.

I once fooled around with subtitles in quicktime and I know I had to have the srt file and the movie file in the same folder to get them to work. As far as getting the titles as a viewing option, I'm not sure. I ripped Apocalypto with handbrake with the subtitles burned in, as far as I can remember I was not able to make it an option of on or off. I have had luck with handbrake and multiple audio tracks such as the directors commentary.

How do I open the avi file in handbrake? I've only used that for dvds. When I try to use the folder/avi file in handbrake it says no valid title found. Any suggestions?

This should do it: http://www.bitfield.se/submerge/index.html