How do you interpret BitTorrent file names?

December 15, 2005 1:58 AM

BitTorrent filter: what do all the letters mean?

The trackers I use often list several different versions of the same thing. I usually go for the file with the largest seed count (on the assumption that most people out there know what they're doing), but I'd like to understand the differences and make my own choices.

So there are two parts to my question:

1. When you look at a list of torrents, (for example, this one), what does it all mean? XviD, HDTV, LOL, HR, BamHD, AC3 5.1, CTU — surely it's all some elaborate practical joke on the uninitiated?

2. The files often vary wildly in size too. Are smaller files always of poorer quality, or do they use better compression? And if, as I suspect, it varies, how do you tell the difference?

Thanks everyone!

posted by londonmark to computers & internet (10 comments total)

1) Either something relating to the format, or something relating to the release group. In your examples, I can spot Xvid (compression format), HDTV (high definition), LOL (name of a release group), AC3 (audio format), 5.1 (audio format). The rest of those I don't know.

2) May be either (or both). How to tell the difference? See point 1.
posted by pompomtom at 2:08 AM on December 15, 2005

• XviD = Open Source Video Codec, equivalant of DivX.... it's usually an avi movie file
• HDTV = High Definition TV... This was captured off of a digital feed, which means that it's probably really good quality, maybe even DVD quality. Usually refers to TV shows
• LOL = probably reference to a release group... Imagine that people who put these files online in the first place are actually pirates, then imagine that they've organized themselves into fleets, so they can accomplish more... LOL would be the name of one group...
• AC3 5.1 = Audio Codec used. Think MP3, only AC3 is a codec for surround sound, and 5.1 means how many channels are encoded...
• The rest, I don't know, probably groups, like LOL

As for file size, the general standard is 350mb per 1 hour TV show (44 minutes), hence 175 mb per half hour show (22 minutes). Movies are generally ripped at a higher quality, so an hour and a half movie (90 minutes) should be at least 700mb... Personally, I rip to about 1,200 mb for a 90 minute movie, but that's a personal preference, since I'm creating my own digital library from my DVDs

Also, some more abbreviations are listed here
posted by hatsix at 2:13 AM on December 15, 2005

Also, HDTV will often simply mean that the source file was HD, so while the file you're downloading might be in widescreen format, it won't be at HD resolution. If you see 'HR.HDTV', the file will be much closer to true HD (though these tend to top out at around 960x540). The difference between these two formats may be what's causing the varying file sizes you noted.

Pretty much any acronym attached after XviD that you don't immediately recognize as video-related is likely to be the release group that posted the file (LOL, CTU, etc.).
posted by toddshot at 2:14 AM on December 15, 2005

The two above me pretty much have it all covered.

In general, 350mb/hour for TV rips is good quality. Anything less will generally look like crap. Although I've found that most Simpsons/Family Guy/American Dad rips are smaller (perhaps the animation compresses more easily?)
posted by antifuse at 2:48 AM on December 15, 2005

really good quality, maybe even DVD quality

err... dvd quality isn't "really good"...

I'm being overly pedantic, because of course there is lots of streamed video that's an awful lot worse than dvd quality... but still, it makes me cringe to hear dvd called "really good".

Technically HDTV should only refer to something at least twice as good as dvd quality (dvd is compressed to 10Mbps, I think the lowest HD format I've heard of is about 20Mbps, ish, someone correct me if I'm wrong. the HD format used by the TV station I work for is XDcam, and this is compressed to about 50Mbps). But I don't really download anything, so I really don't know if you would actually be able to feasibly download something of this quality, or if "HDTV" just refers to something that was hi def a couple of generations back...

So, kinda what toddshot said.

On preview, if 350mb/hour is good quality for a download then you won't get anywhere near dvd quality. I guess it really depends on perspective as to what good quality is, and most people can't tell the difference once you hit a certain threshold... I'll put my hand up first to say that I'm a bit of a snob about quality, but I've been trained to tell the difference, so, *shrug*.
posted by ancamp at 3:04 AM on December 15, 2005

"Snob" is correct. The majority of people downloading torrents would probably watch television shows through basic cable on regular sets if torrents weren't available; 350MB/44min is already better than standard cable television unless you've got an outstanding television. That said, I think there are scene rips that are 700MB/hour (marked with HR, as noted above).

The acronyms in the square brackets often refer to the torrent site, IRC channel or other source of the original file; these serve much the same purpose as the LOL/CTU/etc. acronyms, mainly advertising. I'm assuming you already understand the season/episode codes, but for the uninitiated: 4x09 is the same as S04E09, meaning "season 4, episode 9."

Finally, one more acronym you see occasionally for television is PDTV; this basically means the process used to capture the video is completely digital, and at no point is the signal turned into an analog one. HDTV is the same except that in the case of PDTV, the original broadcast was not high definition.

Movies introduce an entirely new batch of codes. In order of quality from lowest to highest: CAM means recorded in a theatre by some guy with a video camera, and looks/sounds pretty shoddy; TS/Telesync is the same idea except the camera's usually in the projector booth, and the sound is taken directly from the projector as opposed to recorded from the theatre speakers; TC/Telecine skips the video camera altogether and digitally scans the filmprint; DVDrip is self-explanatory. A subcategory of DVDrip is the DVD screener, which is generally as good as a DVD rip but is watermarked with various messages like "FOR YOUR CONSIDERATION" betraying the purpose of the screener (to give members of the Academy something to watch in order to judge the Oscars).
posted by chrominance at 3:38 AM on December 15, 2005 [1 favorite]

On preview, if 350mb/hour is good quality for a download then you won't get anywhere near dvd quality. I guess it really depends on perspective as to what good quality is, and most people can't tell the difference once you hit a certain threshold... I'll put my hand up first to say that I'm a bit of a snob about quality, but I've been trained to tell the difference, so, *shrug*.

It won't be DVD quality, but consider that MPEG 4 based codecs are significantly more efficient than the old MPEG 2 used on DVD video, so it's not as if a 350mb DivX is ten times worse than a 3500mb MPEG 2 file.
posted by wackybrit at 4:24 AM on December 15, 2005

It won't be DVD quality, but consider that MPEG 4 based codecs are significantly more efficient than the old MPEG 2 used on DVD video, so it's not as if a 350mb DivX is ten times worse than a 3500mb MPEG 2 file.

No, but a lot of the time (particularly if the source of the file is outside the USA), that DivX file will have been encoded from a low quality MPEG2 file. I can't understand why people do that, when the gains in size are so minimal.
posted by ascullion at 4:57 AM on December 15, 2005

Thanks everyone, these are all really helpful answers (hatsix and chrominance get the gold stars!) Much appreciated. Sometimes my level of ignorance really scares me. You've inspired me to go and read more about file compression too. Thanks again!
posted by londonmark at 5:36 AM on December 15, 2005

Most tv eps follow the format "Name.SxxEyy.format.codec-group" where format is typically "hr.hdtv", "hdtv", or "pdtv"; codec is almost always xvid, and group is the name of the group that released it.

There are other acronyms for movies and games and so on.

By the way this has nothing to do with bittorrent specifically.
posted by Rhomboid at 1:07 PM on December 15, 2005