Does doing reaction/commenting video of other people videos cause copyright infringement? if so, who is the copy holder of the original video?
<ol>
<li><p>People do reaction video of other people videos, would that make a &quot;huge&quot; different if difference if the people do get permission from the original copyright holder?</p>
</li>
<li><p>Who become the copyright holder of the videos once people upload their online like Tiktok/Youtue/Facebook/Twitter?</p>
</li>
<li><p>What are some ways to obtain a copy right usage from the copyright holder?(when their copyright usage is not public available)</p>
</li>
</ol>
<p>Thank you.</p>

<p>This varies significantly with the law of he country involved.</p>
<p>In the US, creating a video which is composed largely of reactions to or comments on a previous video (the same is true of books or other kinds of works) is often an instance of <em><strong>fair use</strong></em>, and in such cases is not an infringement of copyright. However, if more of the original is included than is needed for the reactions and commentary to be understood, then it <strong>may</strong> be held not to be fair use, and constitute copyright infringement instead. That is a highly fact-dependent matter, which is decided case-by-case, if the copyright owner chooses to bring an infringement suit.</p>
<p>If one gets permission to use a video as part of a reaction video, then it is surly not infringement provided that the terms of the permission, whatever they may be, are complied with.</p>
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<p>Who become the copyright holder of the videos once people upload their online like Tiktok/Youtue/Facebook/Twitter?</p>
</blockquote>
<p>Uploading a video does not change the copyright ownership of the video. The copyright still belongs to whoever it belonged to before the upload. Most often the person who created the video.</p>
<p>It is possible for the agreement permitting upload to include a provision by which the copyright is transferred to the hosting service. But that is quite rare. In the US a copyright  transfer requires a document written and signed by the copyright owner or the owner's authorized agent. What is much more common is an agreement by which certain rights in the video are licensed to the platform on which it is to be displayed. Such an agreement does not change the copyright ownership, but does grant rights, often significant right, to the platform.</p>
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<p>What are some ways to obtain a copy right usage from the copyright holder?(when their copyright usage is not public available)</p>
</blockquote>
<p>By a &quot;copyright usage&quot; I suspect the OP means the right to use the copyright, what is more normnally called a <em><strong>license</strong></em> or simply <strong>permission</strong>*.</p>
<p>The two main ways to get a license are:</p>
<ol>
<li>to ask for it, and have thew owner (or owner's agent) agree, possibly after negotiation on terms and fees);</li>
<li>For then owner to offer a license without being asked, possibly to anyone who will comply with the owner's terms, which may include a license fee.</li>
</ol>
<p>Legally, both of these methods will result in an agreement (usually a contract) that permits use of the work withing certain specified limits and in compliance with specified terms.</p>

copyright copyright-notice copyright-transfer