In this video some guy, who calls himself One Man Sho, sings gibberish while performing various actions such as knocking over wooden blocks and drinking a glass of orange soda. Then the video plays in reverse to reveal that he was actually singing the national anthem backwards.
It would be possible to fake this. For instance, you could dub over the voice, though I imagine it would be a technical challenge to match the dubbed voice to the movement of his lips. Or you could sing gibberish and then dub over the reversed portion of the video. So I downloaded the video to check that the second half really is the first half played in reverse. It is.
So I'm concluding that the video is real. This guy actually memorized how to sing the national anthem backwards. An impressive, but odd talent.
The second half is completely unintelligible noise to me, but then I don't know the American national anthem.
So, I am not too surprised that anyone could sing the American anthem, or any song for that matters, backwards.
W. A. Mozart was known to be able to speak fluently backwards, and I have seen some people who can do it rather effortlessly.
Investigation into the alleged 'backwards masking' of rock songs have shown that regular speech reversed phonetically "says" something completely different. That's how the Beatles singing "Number Nine" becomes "turn me on, dead man" and Queen's "another one bites the dust" becomes "its fun to smoke marijuana". Of course intentional backwards masking is BS.
So, I think Mozart may have been able to say words backwards (as depicted in 'Amadeus'), but speaking fluently backwards (as in it would sound correct forwards) would mean he'd be speaking gibberish as this guy is doing.
So I would say the video is legit. And alot of work to determine the gibberish that phonetically becomes understandable as the lyrics when reversed.
Anyways, I knew a girl once who could say a sentence and then repeat it back immediately backwards. She said she's been practicing since she was a child.