The researcher, who goes by the handle Sealow, detailed his claims in a video on YouTube, providing what he said was evidence of this change which came in during November last year.
A detailed research paper is also avaialble. A total of 800,000 videos were analysed before these conclusions were reached.
YouTube, which is owned by Google, has had issues this year, with major advertisers pulling their ads beginning in March when a report appeared stating that these ads were appearing on videos which had racist, sexist, extremist and anti-Semitic content.
According to his findings, codes are being added to the metadata to indicate different kinds of content. For example the code 102 appears in videos that are being suppressed due to profanity.
Other codes that were spotted were: 104 – sexually suggestive content; 109 – sensational and shocking; 113 – tragedy and conflict; and 115 – sensitive social issues (controversial, guns, etc), according to the blog boingboing.
YouTube has faced additional issues recently, with videos containing scantily clad children showing ads of major advertisers, leading to them pulling their ads.
A Reuters report said hundreds of paedophiles had posted comments below the videos, which appeared to have been uploaded by the children.
It quoted the report as saying that one clip, of a pre-teenage girl in a nightie, had attracted 6.5 million views.
Responding to Sealow's video, one viewer posted: "I wonder what kind of algorithm is working out what is happening in each video and coming up human-like analysis to each video and is showing the trend that Google is censoring 'alternative' content? This seems fairly Orwellian to me."
Said another: "I've suspected this for months. This is definitive proof. (YouTube chief) Susan Wojciciki must be fired for running this site into the ground."