Joined: 4/30/2008
Posts: 89
Location: Northeast Kansas USA, GMT -06:00
I was watching a run of Megaman Battle Network 2 and right in the middle, the movie got cut off, so I went into my torrents and forced a re-check on the file, and it said there were bad pieces in it. Would someone explain why some of the people that use our torrents are giving out bad data?
Not that it matters, but if a seeder sends up ANY piece that fails hashcheck the client bans it automatically. You might as well check your torrents now and see if you have incomplete files or if your client banned anyone.
Follow-up Examination
It appears to affect the archive.org web seeder.
Files may have been slightly altered, or linked to a different source format or material.
This appears to affect only 10-bit 4:4:4 movies.
Any client that CAN'T detect hash failures I would call defective. 90% of the space of a .torrent file is checksum data.
There are a few known scenarios where NAT routers would modify traffic in transit which could cause data corruption. It would render it impossible to finish downloading as everyone you try to download from would cause the same corruption. Furthermore you shouldn't be able to connect to a remote bittorrent user who's downloading the wrong file unless their system is broken as well because the file identity is tied to said hashes and the other user should have checked theirs first.
Someone should independently verify this failure. Sadly I'm calling Not It right now.
I verified that:
- The SHA-1 the torrent file I have matches SHA-1 of the torrent file on the server.
- The SHA-1 of video file I have matches SHA-1 of video file in archive.org collection file metadata.
- The file in the torrent pass hash check against the torrent itself.
All these checks seem OK.
Joined: 4/30/2008
Posts: 89
Location: Northeast Kansas USA, GMT -06:00
Where do I find a setting that does a piece check after finishing the download? This way I don't have my movie interrupted partway and have to go back and check manually.
It seems to be aggravated more when small movies use large (>= 256 KiB) block sizes. Movies should dynamically allocate block size based on the length of the movie, frame size and the encoding used (standard vs. 10-bit 4:4:4). This reduces the chance of a crippling hash check failure, at the expense of more blocks.
Where do I find a setting that does a piece check after finishing the download? This way I don't have my movie interrupted partway and have to go back and check manually.
I used CFV for checking downloads against torrents. But there probably are GUI-based ones too.
GuidMorrow wrote:
It seems to be aggravated more when small movies use large (>= 256 KiB) block sizes. Movies should dynamically allocate block size based on the length of the movie, frame size and the encoding used (standard vs. 10-bit 4:4:4).
The encoding shouldn't affect it, as primary/10bit444 is often approximately the same size. And yeah, the block size should be chosen based on the file size.
Joined: 3/9/2004
Posts: 4588
Location: In his lab studying psychology to find new ways to torture TASers and forumers
GuidMorrow wrote:
Where do I find a setting that does a piece check after finishing the download?
Every torrent client is different, but the good ones should have some kind of option.
In qBittorrent for example, Settings->Advanced->Force recheck upon completion.
Warning: Opinions expressed by Nach or others in this post do not necessarily reflect the views, opinions, or position of Nach himself on the matter(s) being discussed therein.
