General File Questions / .par2 / etc.

[Vectraat]

1.) So I downloaded a video and usually when I do that, It's just the video file itself, but this time the file was accompanied by 10 ".vol" files with different names such as: .vol000+001 / .vol001+002 / .vol063+64 etc.

a.) When I right click on them > properties, I see that these are .par2 files. I assume these were just thrown in with the download for repair purposes if needed?

b.) Yet when I look in SABnzbd and click the downward arrow in "History" I see: Repair: No par2 sets. Trying RAR-based verification -
RAR files verified successfully. Why would SABnzbd tell me that there aren't any par2 sets if there are? Or are par2 sets different than these .par2 vol files?

c.) So I can just delete these .par2 files and the video is likely fine?

c.) Why do some videos include .par2 files while others don't?


2.) On another video (when I click the down arrow) I see: Repair - Quick Check OK.

a.) What is SABnzbd checking over?


Sorry if these questions are noob. I haven't used SABnzbd since 2012 and the other clients I've used function differently. But I'm liking the extra information provided by SABnzbd. I just need to know how to interpret it. Is there a good guide around here discussing what all of this means?

[safihre]

In this case the QuickCheck extracted the par2 verification information and verified the integrity of the download while the files were coming in.
Only if this QuickCheck fails, we start the real par2-repair process that calculates how to repair the files.
In this case it wasn't nessecary.

Sometimes posters do very strange things, where they also include par2 files inside the rar files for some reason.
Maybe you could send me this NZB at [email protected]?

Are you on 2.3.4? Could be that some clean-up of par2 files didn't do it's job. Normally if a job is fine, we cleanup the files.

[Vectraat]

Sure, I sent you an e-mail with the NZB.

[safihre]

The par2 files in this download are damaged, they are not valid so that's why SAB is reporting that it can't find Par2-files.
Luckily we have the fallback of using the Rar-based validation.
If that one succeeds (it's slower) then it also means your unpacked video file is correct.

[Vectraat]

Ok, thanks for the response. I tend to download a lot of stuff off Usenet. If I find any other irregularities should I post here for comment? How do you know they're damaged btw?

[safihre]

You can always post
I opened the par2 files in Quickpar, a Windows GUI for the par2 tool. You could do the same on the commandline on other systems.
It will show that it can't use any of the blocks inside.

[Vectraat]

Slightly off-topic, but if you download a video and SABnzbd says It's "Repairing"

> "Repaired in 11 mins 52 seconds" etc.

Is the video file guaranteed to play ok? Have you ever encountered a situation where SABnzbd said "Repaired" but video playback was damaged in some way?

Is SABnzbd exclusively using .par 2 blocks for the repair process or does it use other data as well?

[safihre]

If it shows "Repaired", then the integrity check of the data has shown that it is now exactly the way it was on the computer of the poster.
So if it was already damaged before par2 files were created by the poster, we can't fix that.

Par2 is the only real file-repair tool out there. You can read more how it calculates the missing data, it's pretty cool math that uses both existing data and the extra data from the par2 files
We don't actually do the repair, we call the par2cmdline or multipar tools (created by others) that do the repair.

[Vectraat]

A few other questions if you wouldn't mind.

1.) Why do downloads sometimes have articles missing? Was this a mistake/negligence of the uploader or is someone trying to remove the upload and they were successful in removing x number of articles?

2.) What does: "articles were malformed" mean?

Examples:

a.) "3 articles were malformed" > "Repaired in 5 mins 26 seconds"

b.) "7 articles were malformed" > Repair: SABnzbd doesn't say it repaired anything as in the above example. SABnzbd only says: Verified in 11 mins 29 seconds, all files correct. Should I be concerned about this download for not saying "Repaired in x minutes x seconds" ?

[safihre]

There can be an upload problem, resulting in missing articles. However, usually it's a DMCA takedown due to copyright infringement.
Malformed means that somehow the article's checksum (each article has it's own) didn't match the data, so somewhere a bit or byte was missing. Maybe during upload or transfer between servers.

Sometimes these malformed ones are not part of the main package but of the par2 files, so nothing actually needs to be repaired of the main data. Or sometimes the checksum data was actually malformed but the data itself was fine. Both cases it doesn't need to repair anything.

[Vectraat]

Oh ok, so even though 7 articles were "malformed" It's likely that everything is ok because SABnzbd didn't need to repair for the reasons you outlined. (par2 files or checksum data are malformed) which won't impact the "main package"

[safihre]

Exactly.
If after the verification there are still problems with the file, then the file was already broken at time of par2 creation on the PC of the uploader.