I made a video in 1080i and it is 25 fps, but when I put in video editor it has twice more frames, as 50 fps video. What could be the problem?
According to Wikipedia 1080i
When 1080p material is captured at 25 or 30 frames/second it is converted to 1080i at 50 or > 60 fields/second
Thats due to the interlaced scan (as indicated by the i) the frame is rendered twice for odd and even lines. If you expect it to have 25fps you should switch to 1080p (p for progressive scan).
To get a solution to your problem you should at least add the exact settings you're currently using.
Currently I don't have 1080i footage available to test the de-interlace option in the VSE, you could give it a try:
The problem is that the file is interpreted as 25fps progressive. But there are twice the number of frames (due to interlacing), Blender represents the interlaced frames as individual progressive frames. Thus doubling the strip length. If you add a speed effect you effectively speed up the strip or discard half the resolution (sort of like deinterlace).
I have a Sony AVCHD camera and could not solve this frame handling issue. The frames must be merged back into each other but Blender doesn't recognise this.