This won't be easy. If you freeze the video, you won't move around in the picture, which is sort of counter-productive. To remove the legs, you have to cut an animated hole in the video, and then replace the missing video with something else.
Do you have video you can put in that hole as a replacement? If you don't, the entire painful process of leg removal is pretty much fruitless.
This is why people shoot on chroma key (aka greenscreen). In your case, you would make sure your legs are your chroma key color. Then you would shoot a background, over which you would then put the video.
The animated hole you said seems like a good idea to me. I have some video to replace that missing video. But how can I cut an animated hole, because masks stay in the same place?
...how can I cut an animated hole, because masks stay in the same place?
You can animate masks by setting a mask path keyframe, then advancing down the timeline, and altering the mask path, which automatically creates a new mask path keyframe. The process is called rotoscoping.
I have to warn you: this rotoscoping stuff is NOT for the faint of heart. It's tough. Before you jump into the deep end of the pool, I strongly recommend you read up on it.
There is a lot of valuable information in that link. Read carefully.
Thank you very much for the information sir. It really helps me out.