As classic an example of compression pumping as you will ever hear...
Let's dive right in with the example...
There are many good features about this video, and it is extremely useful for its intended purpose.
But the audio has a problem. Two problems in fact.
The first is the noise. Clearly the audio is being recorded direct into the camcorder through its built-in mic. If it is a tape-based camcorder, then this could be the reason for the noise.
But also, there is a huge amount of pumping, due to the automatic gain control (AGC) of the camcorder.
When the player hits a note or chord, the AGC kicks in and quickly lowers the gain. But as the notes decay, the AGC relaxes and allows the gain to go up again. The result is that, between notes, the volume swells.
The solution of course is to record the audio separately onto a dedicated audio recording device, then sync it again in a video editing app. Or, if possible, use an external microphone and set the camcorder's gain manually, switching off the AGC.
Of course, either way is more fiddly than straightforward point-and-shoot. Although the results may be better, it might result in fewer videos from this YouTube contributor. Some might say that fewer but better videos would be the way to go. On the other hand, this pianist has set himself a mighty task of recording a lot of music that many people will undoubtedly find useful.