Perhaps the questioner is referring to what Muslim narrated in his Sahih from Jarir ibn ‘Abdillah (may Allah be pleased with him), who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “… And whoever sets a bad precedent in Islam and others do it after him, a burden of sin will be recorded against him like that of those who do it, without that detracting from their burden in the slightest.”
This hadith is applicable to the one who promotes bad things and calls people to them: he will bear a burden of sin like that of those who do that deed until the Day of Resurrection, because he is the one who caused people to fall into that sin, so he will bear his own burden of sin and a burden like that of others.
Allah, may He be Exalted, says: {But they will surely carry their [own] burdens and [other] burdens along with their burdens} [Al-`Ankabut 29:13].
Ibn Kathir (may Allah have mercy on him) said: This tells us that those who call others to disbelief and misguidance will, on the Day of Resurrection, carry their own burdens and a burden like that of others because of the people they misled, without that detracting from the burdens of the others in the slightest.
End quote from Tafsir Ibn Kathir, 6/266.
Based on that, everyone who calls people to misguidance is included in the general meaning of what is mentioned above. That includes the case mentioned here: everyone who participated in producing that bad video, or sent it to others, or told people about it and told them how to get it, is among those who introduced a bad precedent, and they will carry their own burden and a burden like that of those who acted upon it, without that detracting from the burden of the others in the slightest.
As for the one who only watched the video, without propagating it or calling others to watch it, he will only carry his own burden, and not that of anyone else.
Allah, may He be Exalted, says: {And every soul earns not [blame] except against itself} [Al-An`am 6:164] and {And no bearer of burdens will bear the burden of another } [Al-Isra’ 17:15].
Let the one who persists in sin, even minor sins, beware, for persisting in a minor sin turns it into a major sin, and the doer will incur shame and face the consequences of that.
It was narrated from `Abdullah ibn Mas`ud (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Beware of sins that are thought of as insignificant, because they accumulate against a person until they destroy him.”
And the Messenger of Allah (blessings and peace of Allah be upon him) gave a likeness of such sins: the likeness of people who have halted in the desert and the time comes to cook, so one man goes out and brings a stick, and another man brings another stick, until they have accumulated a lot, then they light a fire and cook what they put on it. Narrated by Ahmad, 3818 and others; classed as sound (hasan) by al-Albani.
So let the one who cares for himself beware, lest he collect sticks of firewood for Hell, and a raging fire be lit by means of his bad deeds. Allah, may He be Exalted, says:
{And if you could but see when the angels take the souls of those who disbelieved... They strike their faces and their backs and [say]: Taste the punishment of the Burning Fire
That is for what your hands have put forth [of evil] and because Allāh is not ever unjust to [His] servants} [Al-Anfal 8:50-51].
And Allah knows best.