accelerated image after export

Hello,

When I export my project (H264, 25fps), I get an image that is accelerated compared to the sound. So the end of the exported video (1'42") has about 10 seconds of black screen with the sound still audible.
I did tests, when I export my video at 30 fps it works, there are no more problems.
But since my images are filmed at 25 fps, it totally destructures the video.
Would you have a solution?