Freedom of speech is clearly enshrined in the US Constitution as freedom of restriction from government, but freedom of speech is a fundamental human right. It's kind of an academic distinction if a multinational corporation like Twitter is restricting it or a government.
1) US freedom of speech, which is only freedom from government interference with political speech, and obviously US-only.
2) UN "international" freedom of speech. Has 2 major problems
* cannot actually be used to sue anyone for denying it, unlike the US law
* has been repeatedly judged to not even cover "muhammad is an asshole", despite that obviously being political speech in a third of the countries that signed it. Same goes of Chinese and EU politicians, EU royalty, Thai royalty, and a myriad of other cases.
In political philosophy (at least the standard USA political philosophy I learned in school) rights are things that we agree in principle people should be allowed to do. Laws are made to protect rights, but they are not the source of those rights. Rights are founded in our collective moral beliefs.
Says who? If you believe the Supreme Court, calls to violence are core political speech (Brandenburg v. Ohio, NAACP v. Claiborne Hardware). I'm not even sure what law distributing videos of murder would break.