Audio sync problem in preview/playback

I have the same problem... I think. I'm using 720p matroska video files, and proxy clips, and a separate MP3 audio file. I think the problem is with the audio file.

This is a major pain because I play the file in Kdenlive, and all the video syncs with the audio exactly as I want it. I go to render and it can be miles off.

For the record, I'm trying to make a music video.

I'm using Kdenlive 0.9.4 on a Kubuntu VM.

Anymore information someone might need?

I got a bit of a workaround. Everytime I think I got part of the video looking exactly as I want it, I render the whole thing and take a look. It's a bit cumbersome.

Hmmm... part of me thinks it's a problem with the very newest version, which I just jumped through hoops to upgrade to, since the version in the Kubuntu repositories crashed every time I tried to render.

But this problem isn't with rendering, and the audio doesn't stutter (at least not in my experience). It just floats out of sync with the video in the project preview.

Actually, since you bring it up, it didn't crash when I tried to render. It crashed the moment I pressed the 'render' button. Before the rendering options even popped up.

I made an inadvertent discovery the other day that may be relevant to this topic.

A while back, I wanted to create a video where events in the video were synced to beats in the music track. To that end, I tried playing the music clip in the clip preview window, and then tapping on the '*' key in time with the music, which should have laid down guides on the beat points. However, it became obvious after a few seconds that the guides were drifting and landing in the wrong place.

Last week I tried to more precisely quantify this problem. So I launched Audacity and created a one-minute-long click track at 120bpm. This had the advantage of having audio pulses that would be extremely visible in the editor timeline, and any misalignment between the pulses and the dropped guides would be immediately apparent. I imported the click track as a clip, played it in the clip previewer, and started tapping on '*' for the length of the clip. I then dragged the clip to the timeline to have a look at it.

The guides started out in sync, but soon drifed to a point about 0.25 seconds out of sync and stayed there. So it looks like some sort of playback buffering is causing some bits of the program to run ahead of others.

But here's where it gets interesting. I opened Kdenlive's Configuration preferences window, and clicked on Playback. In there are several options for setting up how Kdenlive renders to the screen. On a whim, I enabled the one labelled, "Use OpenGL for video display," restarted Kdenlive, and tried the same thing again. (I knew I could get away with this because that particular machine has an NVIDIA card.)

This time... the guides landed in perfect sync! There were occasional one- or two-frame errors, but I put that down to my own poor rhythm hitting the button.

So, at least for my experiment, on my machine, there's something about what Kdenlive picks for video display by default that's drifting out of sync. Maybe you could give that setting a try and see if things improve.