I don't know if DoM does frame level hashing while encoding, but the hashes that are stored in the DCP that are read by the cinema servers are hashes of the full MXF and therefore can't be calculated until all frames are encoded. On Mon, Oct 15, 2018 at 4:34 PM Jim Dummett via DCPomatic &lt;dcpomatic(a)carlh.net <mailto:dcpomatic@carlh.net>> wrote: Hi Carl. I have a rather obscure question: At what point in the process of DCP encoding are the hashes calculated? Reason I am asking is that I have been making a large batch of DCPs but now I suspect that one of the drives I've been using is faulty. Some other files on the drive have become corrupt. I've checked that all the DCPs on that drive pass a hash-check, but... are the hashes calculated: 1. As the MXF files are created *before* they are written to disc? or 2. Files written to disc first, and then read back from disc afterwards to calculate hashes? Because DCP-o-matic has the lengthy "calculating checksums" phase at the end of encode, I am suspecting it might be the latter. If it is, then I am wondering if it's possible some of the DCPs I've made are corrupt. I'm thinking that if any of the data got corrupted between DCP-o-matic writing it to disc and then reading it back again to calculate the hashes, the hashes would reflect the corrupted data. And so the fact that my hash-check passes wouldn't guarantee the DCP is as it should be. Or is there some other integrity checking process which would make this impossible? Sorry for rather random question. Many thanks, Jim _______________________________________________ DCPomatic mailing list DCPomatic(a)carlh.net <mailto:DCPomatic@carlh.net> http://main.carlh.net/cgi-bin/mailman/listinfo/dcpomatic -- TOM HAINES Screenings | Originals Publicity M: 310.467.3069 <http://310.467.3069> | thaines(a)netflix.com <mailto:thaines@netflix.com> 5808 W. Sunset Blvd, 5th fl | Los Angeles, CA 90028 <https://maps.google.com/?q=5808+W.+Sunset+Blvd,+5th+fl+%7C+Los+Angeles,+CA+90028&entry=gmail&source=g>

On Tue, 16 Oct 2018, Jim Dummett via DCPomatic wrote: [snip] Number 2. Sadly you can't do it on the fly (as far as I can see) as when the MXF is finished you have to write some stuff back to the header at the start of the file. You're right here, I think. DCP-o-matic does save individual frame hashes as it writes the DCP, but these are only used for resumption of encodes (to work out where the previously encoded MXF stopped being "right"). It could re-check those hashes when it is making the new hash for the CPL/PKL files. In fact it may not be much of a performance hit as that operation is probably limited by disk IO. https://dcpomatic.com/mantis/view.php?id=1380 Best, Carl _______________________________________________ DCPomatic mailing list DCPomatic(a)carlh.net http://main.carlh.net/cgi-bin/mailman/listinfo/dcpomatic

On Tue, 16 Oct 2018, Jim Dummett via DCPomatic wrote: [snip] Number 2. Sadly you can't do it on the fly (as far as I can see) as when the MXF is finished you have to write some stuff back to the header at the start of the file. You're right here, I think. DCP-o-matic does save individual frame hashes as it writes the DCP, but these are only used for resumption of encodes (to work out where the previously encoded MXF stopped being "right"). It could re-check those hashes when it is making the new hash for the CPL/PKL files. In fact it may not be much of a performance hit as that operation is probably limited by disk IO. https://dcpomatic.com/mantis/view.php?id=1380 Best, Carl