FLAC muxed with mkvmerge losing sync

[PDB]

Strange thing and it might just be me forgetting to do something but every flac file I mux into a MKV using mkvmerge goes out of sync. It starts fine but slowly drifts as the video progreses.

That's with flac files I have made, flac files others have made and using different audio programs and especially different versions of mkvmerge.

If I convert the flac to PCM, it will merge fine and remains in sync. Convert it back to flac and it's a no go.

Any idea as to what I'm forgetting?

[deleted user]

Very strange, don't think I ever had that problem unless I set the framerate wrong. Just for purposes of covering all corners, have you tried muxing both the PCM and FLAC at the same time and seeing what happens? How big is the drift across the entire movie length? And does the drift happen in every player and even if you fast forward to a specific place?

[Chewtobacca]

Yeah, that's strange. I've never experienced the problem, but it sounds as if it's something to do with frame-rate. Try setting the frame-rate of the video manually.

[PDB]

Just for purposes of covering all corners, have you tried muxing both the PCM and FLAC at the same time and seeing what happens? How big is the drift across the entire movie length? And does the drift happen in every player and even if you fast forward to a specific place?

Yep tried that. Not sure how big the drift is but enough to be off several seconds at the end. Tired in VLC and various MPC on two PCs with the same results.

Very strange, don't think I ever had that problem unless I set the framerate wrong.

Yeah, that's strange.  I've never experienced the problem, but it sounds as if it's something to do with frame-rate.  Try setting the frame-rate of the video manually.

Let me try the set the frame rate than (23.976 BTW)

Thanks guys

[Chewtobacca]

You might also try ruling out abnormalities in the format of the FLAC file by running it through eac3to.

Code:

eac3to input.flac output.flac

Mux the output, and see if you still experience the problem.