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Any Linux or *nix Users Out There Who Have a CRC Checksum for GhostBusters: Afterlife?
Posted: Thu Feb 17, 2022 6:34 pm
by Faber
I ripped (copied) the 4K Blu-Ray of Ghostbusters: Afterlife on my PC, but unfortunately, I accidentally scratched it a bit on the tray of my Blu-Ray drive before I had a chance to copy it. I'd really like to see if the digital copy that I got from the disc is flawless or if the scratches negatively affected it. I've watched a bit of it and fast-forwarded through it a bit, but I don't want to have to re-watch the whole movie just to find out if the file has been affected by the scratches.
Also, I did some research, and I found out that CRC32 checksums are derived different ways with different tools. I used the *nix tool cksum to get my checksum, so I need a checksum of a scratch-free version of Afterlife made with cksum. I haven't put my copy through Handbrake yet, so the copy of the movie that you checksum with cksum has to be just the ~60GB file that you got from the disc.
Many thanks in advance!
Re: Any Linux or *nix Users Out There Who Have a CRC Checksum for GhostBusters: Afterlife?
Posted: Thu Feb 17, 2022 7:16 pm
by emrysblack
I do have the film myself, but I doubt that a CRC checksum would tell you much as you would expect them to be different from disc to disc as the foil pressings themselves can differ a bit on the bit level (This is why some UHD discs are playable, but not rippable and people suggest replacing even new discs that are clean when it fails to rip). That will mess up any CRC checks apart from from different subs, attachment rip settings that people have on that are different from your own. I would suggest just watching the movie and seeing if any unwanted artifacts show up. If you really want to do a CRC check it would be more helpful to rip your own disc again and CRC the two files from the same source to see if the scratch actually flipped any bits. Even then it's not guaranteed. MakeMKV also logs any difficulties it had reading particular sectors with retries or workarounds so you can always look at that if you are worried.
Although, if I'm wrong about any of this I'm sure someone will swiftly and kindly correct me. Bottom line, just watch the film and see if it's acceptable or not.
Re: Any Linux or *nix Users Out There Who Have a CRC Checksum for GhostBusters: Afterlife?
Posted: Thu Feb 17, 2022 8:00 pm
by Faber
emrysblack wrote: ↑Thu Feb 17, 2022 7:16 pm
I do have the film myself, but I doubt that a CRC checksum would tell you much as you would expect them to be different from disc to disc as the foil pressings themselves can differ a bit on the bit level (This is why some UHD discs are playable, but not rippable and people suggest replacing even new discs that are clean when it fails to rip). That will mess up any CRC checks apart from from different subs, attachment rip settings that people have on that are different from your own. I would suggest just watching the movie and seeing if any unwanted artifacts show up. If you really want to do a CRC check it would be more helpful to rip your own disc again and CRC the two files from the same source to see if the scratch actually flipped any bits. Even then it's not guaranteed. MakeMKV also logs any difficulties it had reading particular sectors with retries or workarounds so you can always look at that if you are worried.
Although, if I'm wrong about any of this I'm sure someone will swiftly and kindly correct me. Bottom line, just watch the film and see if it's acceptable or not.
As I said earlier, I accidentally scratched the disc before I ripped it, so I don't see how ripping it again and comparing its checksum will help. But thank you for the information about materials.
Re: Any Linux or *nix Users Out There Who Have a CRC Checksum for GhostBusters: Afterlife?
Posted: Thu Feb 17, 2022 11:32 pm
by emrysblack
The scratch could result in random data being read back if it were affecting any of the data of the film, so a CRC check against yourself would differ in such a case. If it came back the same, you could be reasonably confident the scratch didn't affect the part of the disc you were interested in. Which is why I suggested it if you really wanted to investigate with a CRC.