maybe someone would help me.
Im trying to add some movies to my itunes library, and i have my files into .avi format(works properly in other media player) and when i convert it using quicktime onto .mov, the sound is missing.
everything else remains the same, only the sound.
any clues and suggestions of why this is happening?
As has been explained many time before in this forum, AVI is a file container—not a compression format. What you can do with the AVI file depends on what kind of data is stored in the AVI container. For instance, QT X v10.3, QT X v10.4 and QL under Mavericks and Yosemite only play AVI files containing Motion JPEG video along with any supported form of compressed audio like linear PCM. Any other combination of compressed audio and video combination in this file container would would either be unsupported by the AVFoundation in the latest operating systems or force a conversion—i.e., the AVFoundation would pass the file on to the Modernizer routines to see if the content can be converted to a file containing compressed data that is QT compatible.
Depending on the type of compressed data contained in the AVI and the codec support installed on your system, the Modernizer will either terminate its conversion attempt and report that it can't convert the file or it will pass the file on to the Convert routine for conversion. For instance, a common DivX/MP3 AVI file would probably not be converted on a recent operating system with only native codec support. However, if the system has the Perian (or similar) codec package installed, then the Modernizer would recognize that Perian (or other) codec support was available and pass the file on to the Convert routine for a successful conversion. Unfortunately, there are some exceptions. For instance, files containing DTS audio are usually trapped by the Modernizer if Perian is not present but are passed on to the Convert module if it is present since Perian contains DTS codec support. Unfortunately, this support is not compatible with the Convert routine under the two latest versions of Mac OS X and ends up creating an "empty" audio track.
If this is the cause of the problem in your case, then the solution is simple, use a third-party converter as was already mentioned. I would recommend any that use the FFmpeg package for codec support. Many such utilities are available. My personal preference would be the free HandBrake app which includes many presets for the novice user, as well as, advanced features for the prosumer or professional user making customized conversions of specific content and/or for a specific targeted use and can retain chapters, multichannel audio, and/or subtitles (if available in/to the original file) in an anamorphic or non-anamorphic rendering using the basic GUI and/or line-oriented settings. (I.e., properly used, this is a very powerful utility.)