Different length for audio and video tracks after transcode?

[Sound]

Hello all,
I'm capturing clips from a DVB device and transcoding them to MP4 files (I need to open them with QuickTime, so they must be regular MP4+mp4v+aac files). This is the command I use:

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vlc dvb:// --dvb-adapter=0 --dvb-bandwidth=8 --dvb-frequency=602000000 --program=44 --sout '#transcode{vcodec=mp4v,acodec=mp4a,vb=300,scale=0.4,ab=64,channels=2,deinterlace,audio-sync}:dst=standard{access=file,mux=mp4,url=file.mp4}'

However for 1hour+ clips I get audio/video sync issues. By inspecting the files with QT Player Pro I see that the audio and video tracks have different lenghts! For example:

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Audio track length: 1:59:25.40 Video track length: 2:16:57.22

Why does this happen? How can I force them to be of the same length?
Thanks in advance!