We are not likely to know what went on before what is shown in this video that may have provoked the Chinese.
Let's take a hard look at several of the frames of the video itself.
IMHO, unless that Vietnamese vessel had done something similarly life-threatening to a Chinese vessel or structure, there was no excuse for what happened here. Even if the Vietnamese ship was near a Chinese oil rig. Even if they harassed a Chinese vessel...unless of course they tried something similar and put Chinese lives at risk.
As I say, we do not know the provocation...but that is clearly what happened, and, IMHO, it cannot be sugar-coated by anything on that video.
Is it not all a matter of perspective?
These Vietnamese vessels have repeatedly entered the declared exclusion zone around China's Oil Rig, a national economic asset. Their hostile intent toward the asset is clear via Vietnamese Government statements on the matter and the attempted approach to the Rig by numerous vessels, despite Chinese Coast Guard warnings.
Now were this a US Oil Rig being approached by a multitude of similarly hostile ships, say from Venezuela, would the USCG not warn them off? The difference being vessels disregarding a USCG warning and subsequent arrest attempt would be shot at and forcibly stopped. The USCG would never allow hostile ships to approach a US owned Rig let alone board it (which is the inevitable conclusion).
China understands it's situation and that it cannot shoot first, even in a policing action. So it is using other means to dissuade repeated Vietnamese aggression against the Oil Rig. What else can they do?
If the Chinese ships took no physical action of deterrent and let the Vietnamese vessels continue on through the exclusion zone to the Rig, invariably you would have Vietnamese citizens/activists/naval personnel boarding the Chinese Rig. At which point you would have a much more dangerous situation to de-escalate.
China is pressing it's territorial interests to be sure. But it also has a strong case which include historical facts to back up those interests. My view (which may go against the grain) is that China is being fairly restrained in the actual level of physical force applied in these various circumstances - those of it's making and the making of others equally. We have seen how others in the region deal with conflicting issues from time to time - Philippines v. Taiwanese Fishermen for example.