Is there a way to handle 2 different frame rates in the VSE? 99% of my footage is 24p, 1% is in 25p. My editing is in 24p, audio from the 25p footage is out of sync. If the VSE can't handle it, do you know of another open source software who could do this? Many thanks.
If you can, just separate both into two separated scenes rendered at different frame rates. This will be the case if your final footage doesn't change too often (ideally, one time).
If the amount of footage is manageable, use the speed control effect strip to make both the same speed.
Otherwise, put all your raw 25fps into one large edit and render it at 24fps. Now you can import it into your actual project and edit it like the rest of the video.
I assume that your render is set at 24 fps. If this is the case, and your 25 fps strip has audio included, you should see a small difference in length between that 25 video strip and its corresponding audio. If not, you should set your render at 24 fps.
I had a similar problem, having to mix 50 fps strips with 30 fps strips.
According to samblers answer to this question, you could insert a speed effects strip over your 25 fps strip to downspeed it and make frames match with your projects render (and with strips corresponding audio). I think you should set speed modifier to 1.04 (25*100/24=96 - 100-96=4). That should make your 25 fps strip equivalent to the 24 ones. But that math didn't work for me. I had neither time nor necessity to have an awesome quality video rendered, so I just tried different speeds until it looked just well.
Surely someone else can improve this answer, I hope it helps you getting forward with your job.