I have this problem when mixing video (mp4) and audio (wav) on the timeline. When making sure that the video and audio is perfectly aligned on the timeline (precision: With in 1 keyframe), the audio always is 3-4 keyframes out of sync, when the project has been rendered (mp4).

Now I did some testes, and it's easy to blame the rendering engine, but I think the issue is the timing during the previewing (e.g. kdenlive sending audio and video with different delays to ffplay).

For me to correct the error, I have to move the audio track (wave file) 3-4 frames forward. Then the audio is out of sync, during editing (preview), but in sync after rendering.

My setup:
kdenlive 19.04.3 (same thing with version 19.04.1).

Ubuntu 19.04
CPU: AMD Ryzen 7 2700
GPU: RX580
Onboard audio card.

Thanks for reporting. We are aware of it. If you like you can test the daily build from today. Yesterday we inplemted an "audio sync" parameter in the clip properties which you can adjust.

@Merlimau

I see what you have done, and it's nice, but dos note really solve my issue. I have two separate clips (one audio in wav format, and one video in mp4 format). It is not one file, so fixing it on clip level, dos not really solve it. As I said, when paring the clips in the timeline, it look fine, but after rendering the A/V sync is off by 3-4 frames.

Interesting.
What type of MP4 (1080p50) and wav (44100Hz16bit) do you use?
How long are the clips and the video in total?

I have tested with different formats of both video and audio:

Video (input file): Mp4 (Sony XAVC-S (.mp4) and -L (XDCAM .mxf)) 1080p or 4K both in 25 frames progressive, 8-bit or 10-bit color depth, 422/420.

Audio (inputfile): Wave (48000Hz, 32-bit or 24bit, mono/stereo, from Audacity or from external recorder. But it make no difference what software it comes from.

It's also important to note, that if the video file (mp4) is edited with it's own audio track, then there is no issues. It's ONLY when I try to mix the external video track with audio on the timeline, that this issue appears.