If you transcode and encode the same video to another codec, it will inevitably lead to quality degradation due to the nature of video compression.

So, if you have an HEVC video and transcode it to AV1, then transcode it again to HEVC, you will lose quality at each step: first from the original BD to HEVC, then from HEVC to AV1, and from AV1 back to HEVC (resulting in blurriness, pixelation, etc.). That is why a visual side-by-side comparison of sample frames is the most efficient way to assess quality loss.

The question is clear enough to understand, so be a ware of fake users just fusing around to get attention.

There is no method to determine the previous codec from the final file alone.

The only way is to get the person encoding the file to tell you that it originated from an HEVC source (in your case) but then, what tells you that HEVC used for the encode was not itself reencoded from a VP9 source? That that VP9 encode was not also reencoded from NVENC (h264/h265) source? Etc.

SOURCE => NVENC => HEVC => VP9 => HEVC : could you tell that last HEVC took this road to "be" ? Nope.

So no, there's no magical way to get any certainty, you can only assess the damage.

Thanks for your response.

I very much understand the abbreviations, it's that your question was very poorly worded. And the answer below is quite simply misconstrued.

Why would you respond to a question if you do not understand the abbreviations or the question itself. Any way i already have my awnser.

Yes, I thought that would be the case. Thanks.

The only way is to use forensic tools and perform a side-by-side comparison. You will need to have an original and a supposedly re-encoded version. Once encoded and altered, the 'new' video can be re-encoded to another codec, assuming new properties. I Hope it helps, seek for forensic video tools.

Sorry if my answer wasn't up to your standards, it's just that your question itself is very confusing. What do you mean by "some other x264"? Could you perhaps word it a little better? People here also have no idea what this "AI" you're mentioning has said.

EDIT: Did you perhaps mean something along the lines of: "How to tell if a remake/re-encode has been re-encoded to AV1 or some other codec?" I'm really trying to understand what you're asking. Maybe an example would help...

Thanks, but AI already mention mediainfo and about the tag from nyaa will not apply to downloaded shows.
About your statement "The codec (HEVC/H.265/x265, AVC/H.264/x264, AV1 etc) don't really matter...", is not true, it matters for some of us and that is the point of the question.

Please, if someone else has a more academic answer, feel free to comment, thanks.

The "Remake" tag on nyaa (which looks like this here) is the first indicator that a release was re-encoded more than once. However it's not always respected, so the description is just as valuable to tell if it's a re-encode. And you can check the mediainfo for any clues of leftover metadata giving out which release was used as a source, like the track names. The codec (HEVC/H.265/x265, AVC/H.264/x264, AV1 etc) don't really matter since you can freely encode from one to the other.

How to tell if a video HEVC was re-encoded to AV1 or some other x264?
Please don't paste respose from AI, i would like to know from personal info or technique.
Thanks