soundproblem

[13bc08]

Converting a vob-file from a dvd into m4v-file. All well. Putting into dropbox. Streaming with dropbox on iOS: all well. Downloading the file from dropbox in iOS (iPad e.g.): --> no sound. The same by importing the same m4v-file into iTunes: After syncing with iPad or iPhone: --> no sound while playing the file.
If I do in the same way with QuickTime: There isn't this issue with the sound, but the same files are much more bigger as when I convert it in vcl.

Any idea??