For example now a days in some TV programs, some pornography or some other videos on YouTube contain kufr and shirk and even in some books and in some websites there is some kufr or shirk in it. So is it kufr or shirk if someone reads or watches something that contains kufr and shirk in it ?
Even strict fatawa claim this is not kufr (and it follows it's not shirk either). In fact, IslamWeb directly addresses this topic:
A Muslim is not considered an unbeliever just because of watching films that contain matters of Kufr, but this does not mean that it is permissible for a Muslim to watch them ...
Nevertheless, they're clear that there's many inherent problems:
... so some viewers may develop doubts that damage their eemaan and shake their belief; they may start to believe some of the false ideas and their hearts may be filled with evil poisons as a result of watching these movies. ...
... When the Muslim indulges in reading these books or watching these movies, it shakes his belief or at the very least wastes his time and keeps him busy with something that is of no benefit to him. ...
In general, it's not a straightforward matter to commit shirk or kufr. Al-Azhar University prepared The Response (pdf, online); it's description says: ... its aim is to contest the growing number of intolerant and/or simply mistaken legal opinions that often go unchallenged in Muslim communities today. One of the key topics they address is the widespread notion that one can easily slip into disbelief.
Sins committed by a Muslim, be they deadly or trivial, do not render a Muslim a non-believer. This is supported by the Qur’anic verse:
“Lo! Allah pardoneth not that partners should be ascribed unto Him. He pardoneth all save that to whom He will”. (Q. 4:116)
According to the Fatwa Centre, supervised by Dr. ‘Abdullah al-Faqih:
... a disbeliever can only be, therefore, an adult of sound mind, who is fully aware that he is committing disbelief unexcused by ignorance or based on claims of interpretation in issues that are open to interpretation or are not widely known.
Dr. Muhammad Fouad
Shirk is a grave matter. We cannot trivially call things Shirk. And there is no reason or evidence to consider watching videos or movies Shirk. But, that does not mean it is good or allowed to do. Drinking alcohol doesn't make you a Mushrik, but it is still haraam.
First of all, about pornography, that is definitely forbidden:
Tell the believing men to lower their vision and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do. (24:30)
Do not give a second look, Ali, (because) while you are not to blame for the first, you have no right to the second. (Abu Dawud)
If we can't even look at the opposite gender directly... it is definitely forbidden to watch pornography.
Watching youtube videos, movies, and TV shows does not make you a Mushrik or Kafir, but there is definitely evidence that it is a sin to watch useless things:
In gardens they will ask one another (40) Concerning the guilty: (41) What hath brought you to this burning? (42) They will answer: We were not of those who prayed (43) Nor did we feed the wretched. (44) We used to speak uselessly with those who spoke uselessly, (45) And we used to deny the Day of Judgment, (46) Till the Inevitable came unto us. (47) (Al-Mudathhir)
Wasting time discussing or listening to uselessness is mentioned along with everything else that are clearly sins.
And it has already been revealed to you in the Book (this Quran) that when you hear the Verses of Allah being denied and mocked at, then sit not with them, until they engage in a talk other than that; (but if you stayed with them) certainly in that case you would be like them. Surely, Allah will collect the hypocrites and disbelievers all together in Hell, (4:140)
Many shows and movies openly deny the God. And even worse, many openly mock him. How can a person in good faith give their time up to watch such videos (except to actively correct them)? It would be a sin as it is against Allah's commands.
Then which of the Graces of your Lord (O man!) will you doubt (55) This (Muhammad SAW) is a warner (Messenger) of the (series of) warners (Messengers) (56) The Day of Resurrection draws near, (57) None besides Allah can avert it. (58) Do you then wonder at this recitation (the Qur'ân)? (59) And you laugh at it and weep not, (60) Wasting your (precious) lifetime in pastime and amusements. (61) So fall you down in prostration to Allâh, and worship Him (Alone). (62)
Wasting time is no good, when you can be doing useful things. As Allah himself commands you in the above Ayah, worship Allah more if you have time. Don't waste it on dubious activities.
And it has already been revealed to you in the Book (this Quran) that when you hear the Verses of Allah being denied and mocked at, then sit not with them, until they engage in a talk other than that; (but if you stayed with them) certainly in that case you would be like them. Surely, Allah will collect the hypocrites and disbelievers all together in Hell, [Qur'an 4:140]
We find in many places in Qur'an advising us not to do / get involved in Kufr / shirk / polytheism / ill practices / Fahsha etc.
Hence, according to verse quoted above, it is not allowed for us to witness or be part of anything that is against which is taught in Qur'an.
If by watching you mean supporting then yeah it does.
Let's say we were watching porn, now, does watching this filth support the producer of porn in any way? Well, the answer is "it does". "You say how?" When you watch them the views count and the more views you know the rest. So when you're watching or reading anything bad and it supports the producer of it then yeah it is a sin according to this ayah:
And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah ; indeed, Allah is severe in penalty. [5:2]
I don't know why you would think that. The Quran states:
Behold, those who are bent on denying the truth and on evildoing - God will indeed not forgive them, nor will He guide them onto any road. (4:168)
And whenever there came unto them a [new] revelation from God, confirming the truth already in their possession-and [bear in mind that] aforetime they used to pray for victory over those who were bent on denying the truth -: whenever there came unto them something which they recognized [as the truth], they would deny it. And God's rejection is the due of all who deny the truth. (2:89)
Verily, it is We who bestowed from on high the Torah, wherein there was guidance and light. On `its strength did the prophets, who had surrendered themselves unto God, deliver judgment unto those who followed the Jewish faith; and so did the [early] men of God and the rabbis, inasmuch as some of God's writ had been entrusted to their care; and they [all] bore witness to its truth. Therefore, [O children of Israel,] hold not men in awe, but stand in awe of Me; and do not barter away My messages for a trifling gain: for they who do not judge in accordance with what God has bestowed from on high are, indeed, deniers of the truth! (5:44)
Verily, those who [despite all evidence] are bent on denying the truth - [be they] from among the followers of earlier revelation or from among those who ascribe divinity to aught beside God - will find themselves in the fire of hell, therein to abide: they are the worst of all creatures. (98:6)
What you would recognise from the Quran is that Kufr - or disbelief - is the active and continued rejection of God's "clear signs", which are supposed to leave no room for any doubt. It is for this reason that the kafir is NOT A NON MUSLIM, but a "concealer". The other meaning of a "kafir" in the Quran is those who historically prevented Muslims from following their religion by persecution.
And the inmates of paradise will call out to the inmates of the fire: "Now we have found that what our Sustainer promised us has come true; have you. too, found that what your Sustainer promised you has come true?" [The others] will answer, "Yes!"-whereupon from their midst a voice will loudly proclaim: "God's rejection is the due of the evildoers who turn others away from God's path and try to make it appear crooked, and who refuse to acknowledge the truth of the life to come!" (7:44-45)
Shirk, on the other hand, is understood by some as idol worship after the message of God has become undeniably true, or those who set up idols of men (ie, hold their own brethren at the level of God):
AND WE BROUGHT the children of Israel across the sea; and thereupon they came upon people who were devoted to the worship of some idols of theirs. Said [the children of Israel]: "O Moses, set up for us a god even as they have gods!" He replied: "Verily, you are people without any awareness [of right and wrong]! (7:138)
And, lo, Luqman spoke thus unto his son, admonishing him: “O my dear son! Do not ascribe divine powers to aught beside God: for, behold, such [a false] ascribing of divinity is indeed an awesome wrong! (31:13)
VERILY, God does not forgive the ascribing of divinity to aught beside Him, although He forgives any lesser sin unto whomever He wills: for he who ascribes divinity to aught beside God has indeed contrived an awesome sin. (4:48)
You don't seem to fit any of these descriptions, do you?
What you also ought to remember is that movies, magazines, and books come centuries after Muhammad and his claim of Prophethood. There is therefore nothing that PROHIBITS you from reading and watching anything in the Quran, but you may infer that something - eg. pornography or even terrorist propaganda - may not be good for you. The Quran exhorts you to think:
Verily, We have shown him the way: and it rests with him to prove himself either grateful or ungrateful. (76:3)
Therefore, if you choose to disassociate with someone or something simply because of their different beliefs is unjustifiable. The Quran tells us:
As for such [of the unbelievers] as do not fight against you on account of [your] faith, and neither drive you forth from your homelands, God does not forbid you to show them kindness and to behave towards them with full equity: for, verily, God loves those who act equitably. (60:8)
Therefore, if Muslims are told that they can love and be kind with non Muslims - who follow a way different from Islam - and still remain Muslim, then what makes you think watching a movie could change you in the eyes of your Lord, whose children we all are? On the other hand, you could make a conscious decision not to watch something immoral, such as material encouraging violence, racial hatred, or complete nudity. It is up to you, but don't fall into the trap of believing extremists who cannot justify their false claims with the Quran.
May God bless you and establish peace in this world. I hope this answered your question :)