Subtitling existing MP4

[iaefai]

I have an MP4 file and an srt/ass (both) and I would like to add it without having to reencode the file.

I know I can use handbrake, but it definitely would be reencoding and thus less than ideal.

I do not want burned in subtitles, only a text subtitle track. I haven't even found a way to add it to quicktime.

[poisondeathray]

yamb or mp4box to add softsubs

not all players will support soft srt subs in mp4 container

mkv container is better for this purpose (mkvtoolnix)