AV syncs fine in MKV, but slightly off in mp4

[Bipolarbear]

I have what I think is a bizarre observation here. I've ripped certain DVD tracks using Handbrake and I usually select mp4 as the container. 95% of the time it's just fine, but with several tracks the AV is just slightly off. Several times now I've managed to solve this by re-ripping with all the same settings but choosing MKV as the container, and this has alleviated the syncing problem entirely.

Now I've read repeatedly they are only containers, they have no bearing on the encoding within. I'm wondering if anyone else has ever experienced anything like this.

[Bernix]

Hi,
because it is container, so it contains information about video and audio and other files. It means for example audio delay. I encounter problem when I did Audio in separate program and then muxed it in Mkvtoolnix. I almost always have to shift it -500 ms to get sync audio with video. But never seems it in mkv with normal setting usual AAC when encoding at once. So it is not answered MP4 issue but at last that it is responsible for delay of tracks too (container)

Bernix

[Bipolarbear]

Thank you. So it's not absolutely unheard of then.

[Bernix]

Hi,
no, the if the sync problem is the audio is shifted, not in case Good sync at start and bad on end. If the sync is same on start and at the end that is in header of muxer. You can correct this in my favorite Avidemux. There is under Audio output shift with millisecond precision.
You would not need to recompress that file. Just muxing Copy video copy audio. If you want mp4.

Bernix

[Bipolarbear]

It's hard to explain exactly what's going on. It definitely does not get progressively worse, it's the same from beginning to end but there are times also where the audio seems briefly in sync. It's almost as though the frame rate is far lower than the source, yet I have selected " same as source" for the CFR. It looks like the frame rate is inadequate to keep up with the audio but they don't get further out of sync. It's very hard to describe. But whatever it is, changing the container fixes it. I just don't really understand what's going on.

[Bernix]

Oh,
and dont use VFR aka Peak framerate, which is default. Causing lot of problems when not played on PC !!!

Bernix