audio and video not in synch when merged

[Disturbance]

ok starting off, i have the raw vobs and ac3 files ripped onto my computer, a quick mkvmerge shows that they are in synch for the entire episode, now when both are encoded:

Compression: MPEG-2
TV system: NTSC
Aspect ratio: 4:3
TV system: not specified
Display mode: 720x480
Dgindex indicates it is 29.97FPS

video gets encoded to h.264 mp4

and the audio via besweet->0.3q ogg 2.0

now when they are merged together from the encoded video and audio the audio as the episode continues to become out of sync, it starts off right and then as it coninues goes more and more out of synch,

anyone got any idea how i can fix this. i have used many different encoders, and converting to diff formats


thanks in advance