VSE: Imported audio not in-sync with video after 10 minutes

I use the Blender VSE for overlaying live video footage from a camcorder (with noisy audio from the camcorder) with good quality audio straight from the mixer, captured at a live event.

I need to manually align the two audio tracks, after which I remove the camcorders' original audio track.

However, after 10 minutes, there's a lag between the two. It slight, but annoying. After 20 minutes, it's symply out-of-sync.

Q: how can I avoid this difference?

Tried so far: -The problem appears in both the preview and in the rendering. (so it's not just down to the av-sync button) - The frame rate of Blender's rendering and the video match: 25 fps - The recording frequencies of both the audio-file and the video file are 48000 Hz - The video has a constant bit-rate

Camcorder track (video):

Stream #0:0: Video: h264 (Constrained Baseline), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)


Audio track:

Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 2 channels, s16, 1536 kb/s

• Small sampling differences add up quickly sorry. – 3pointedit Nov 18 '17 at 23:32
• @3pointedit Thanks for the comment! With 'sorry' you mean: there's nothing we can do about this? – Ideogram Nov 19 '17 at 9:05
• Yup... sorry. Best option would be to resample the audio but blender can't do that, also you don't know if the fluctuation is variable. You could try changing the Audio Strips Pitch value, but I don't think that it will give you a fine enough change. And the pitch will alter of course. – 3pointedit Nov 19 '17 at 11:30
• @poinedit If you say, "Best option would be resampling". Sure, can do that in audacity. But what should I resample it into? Current: wav @ 48kHz. Or is it maybe the video that should be resampled. Your comments are already very much appreciated! – Ideogram Nov 20 '17 at 7:30
• Looking at the codec parameters it looks correct. Hmmm, when we shoot stuff for TV we sync long recordings so that they do not drift from each other. This involves using a video sync lead between recording devices. You may have to manually break the audio and resync to video at regular periods, sorry – 3pointedit Nov 20 '17 at 8:35