Steinway of course, you can hear so much more detail.

since i'm looking when the pianist switch from CFX to Steinway, the Steinway has more refine sound and more magnificent...i'm not a pianist and using only a digital piano using VSL plugins with Bosendorfer and Steinway....but if blindfolded it'll be hard to distinguish but the sounds are separable

I'm not sure as you placed the Yamaha in front of the Steinway so the Yamaha projects somewhat more. They're both fine pianos. So, whichever you choose is fine and may just depend on action, responsiveness, tone control, pedal feel, etc.

How can the sound be compared if the audio if of so low quality?

For me, the mic-ing of the pianos seems stationary and thus the Yamaha sounds louder and brighter and I think the voicing of the Yamaha needs a bit of work to make this a more fair comparison. Then there is the placement of the two instruments. This placement I find problematic and does not lend itself to fairly comparing the sound of each piano. That is the trouble with these types of comparison videos. Each instrument is a fine example of the craftsmanship of there makers. When listening I turn down the volume when the Yamaha is played and the difference between the two sounds becomes barley distinguishable.