I found the solution.
When I load the track in the avplayeritem, that is divided in an "array" of audio, video, timecode ( if present ). In case of video loaded from iTunes, the file had video, sound, timecode and I must load the sound part in the audiomix. Before I discover that I load the avplayeritem[0] but it's wrong because in the file loaded from document library the sound part is in another position. That's the solution:
//load the sound part in an array
audioTrackssx = [videoSinistra tracksWithMediaType:AVMediaTypeAudio];
//the sound part must be only one
[audioInputParams setTrackID:[audioTrackssx[0] trackID]];