file_hash questions

[Camille Moulin]

Hi Tom,
On 22/09/2020 07:43, amindfv at mailbox.org wrote:
> Apologies if this is answered in the docs - a quick search didn't uncover the answers.

Generally speaking, the documentation of the file format could be
improved :-(


> I'm wondering about the "kdenlive:file_hash" property in the file XML:
>
>   - Which hashing algorithm is used?


From what I understand, it's seems to be md5, but, for performance
reasons,  it's calculated only on the first and last Mo of the file if
the file is bigger than 2Mo

In ./src/bin/projectclip.cpp, starting line 820:

>         QFile file(clipUrl());
>         if (file.open(QIODevice::ReadOnly)) { // write size and hash
> only if resource points to a file
>             /*
>              * 1 MB = 1 second per 450 files (or faster)
>              * 10 MB = 9 seconds per 450 files (or faster)
>              */
>             if (file.size() > 2000000) {
>                 fileData = file.read(1000000);
>                 if (file.seek(file.size() - 1000000)) {
>                     fileData.append(file.readAll());
>                 }
>             } else {
>                 fileData = file.readAll();
>             }
>             file.close();
>            
> ClipController::setProducerProperty(QStringLiteral("kdenlive:file_size"),
> QString::number(file.size()));
>             fileHash = QCryptographicHash::hash(fileData,
> QCryptographicHash::Md5);
>         }

>   - When are the hashes checked? E.g. if I save a kdenlive file, quit, then reopen it, will the hashes of the files on disk be checked?
Yes, I think so
>  Are there other points at which it's checked? Can the user manually start a check?

I guess that if you reload the clip, it will check it and update it if
modified.

HTH,

Camille