Audio desync after a while on Mpeg TS

[Liss0]

Hello,
I have multiples TV recordings (some in HD) and when I'm trying to convert them, there is an audio delay at the end (the beginning is nice) wich approximately is 6sec/hour of video.
Every time, the audio end before the video (it appears there are some glitches : video plays sometimes superfast but it doesn't link with the audio ending sooner).

I use ffmpeg to convert videos : the problem is the same whether the codec is xvid + mp3 or x264 + aac.

Any idea where the problem can come from ?*
Thanks in advance,
Louis.

* note that i succeeded doing that on others videos after demuxing them with ProjectX (that won't work with HD files)
Maybe it's a FPS prob but MediaInfo indicates 25fps for all


Edit:
Okay, just saw what MediaInfos gives me :

Orginal.ts
Video : 59:58
Audio : 59:58

Transcoded.mp4
Video : ? (according to VLC and MediaPlayer : 1:00:02
Audio : 59:55