From 700 m (2310 ft) to zero in 20 secs, means 6930 ft/min???
It means 126 Km/h and 70 Kts
It only means that average vertical speed was 70 kts, it says nothing about their final speed at the time of the crash.
hat's only covering about 150m in 4s, so it's not hitting very fast: about 80 knots
Again, this assumes the video is shown to us in real-time speed, it doesn't have to be the case. Also, their final speed as registered by FDR was around 245 kts - so I would stick with this.