I have a file which from progressive 24fps was rendered into a h264 high profile 60fps file by mistake. This can be clearly seen advancing frame by frame because every other frame is duplicated except sometimes there are four equal frames. Is there any software able to drop those duplicates frames producing a 24fps stream without encoding again? Is this possible at all or would those frames depend on previous ones, making it impossible?
Almost all encoded frames depend on the surrounding frames, so it's virtually impossible to delete anything from the encoded output without negatively affecting the video. Short answer: no, you can't do that.
One consolation is that true duplicate frames cost almost nothing in terms of file size. They can effectively be represented by a short sequence that means "repeat previous".