I heard that is possible to put a copyrighted music just for few seconds in my youtube (or in soundcloud track) video without infringing copyright laws...is that true? How many seconds? Where can I found these rules?

 

where you located...in EU ...i dont think so

further in youre yt means a video of yours ?
soundcloud is another thing

 

Internationally is recognized a "Right to Quote", as set forth in the Berne Convention, article 10: "It shall be permissible to make quotations [...] provided that their making is compatible with fair practice, and their extent does not exceed that justified by the purpose". National legislations usually provide their own wordings and variations to "copyright exceptions". European copyright law covers some of the practices known elsewhere as "fair use". Always state "credits"! When in doubt about practice appropriate under the circumstance, contact owner of the copyright in question. Be your own judge, not your own lawyer.

 

Amen

 

There is No or Never has been an "Allowed amount use of copyrighted material" without the permission of the copyright owner....What you contend is a Myth...a Legend..a Rumour...that IS Not True.....that had been done by some a long time ago "illegally" with the point of finally getting caught AND procecuted. So the Point of Permission!

"Being your own lawyer puts you in front of someone else's judge"!

 

It's possible to put an entire song there, copyrighted or not. If the copyright holder decides that they don't want it in your video, the sound will be muted for that portion of the video or they may choose to display ads, but it's rarely a reason for a takedown, if your video contains more content than what belongs to the copyright holder.
Copyright strike is issued only on grounds of DMCA request.

No. There is something called "Fair use" under US Copyright Act. Also the aforementioned right to quote.

 

It is one thing to do a rearrangement of someone else's tunes and give credit to the composers. It is a totally different thing to take someone else's music whether it is five seconds or more and call it your own.
I see a lot of music up there that is the CD's we all can buy as end users.
So if all you are asking is if you can put it up and give credit to the composer's, perhaps ask youtube and/or the people that have not received a copyright infringement notice how to go about it? It is quite possible that the people that have put entire CD's on youtube have not been caught yet, but asking never hurt anyone.

 

Correct.

Also correct, however often in infringement on author's rights.

Bottom line.

 

Amen