Giz Explains: Every Video Format You Need to Know

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Giz Explains: Every Video Format You Need to Know

                               
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from Gizmodo: Top by matt buchanan

                               
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  Onceupon time, video codecs and formats were really only the concern of AVnerds, anime freaks and hardcore not-so-legal movie downloaders. Now,even the most part-time of geeks has to deal with them, whether they'retrying to stream a flick across their house with an Apple TV, dump somevideo onto their phone or just trying to grab last night's episode of Dexterbecause they, uh, forgot to renew their Showtime subscription. It'smessy and annoying, but we're here to clean it up. Take a deep breath.
You might recall our discussion about video bitrates earlier,or how much data is packed into a file. As a general rule, more bitsper second translates into more betterer quality audio and video. Thevariable in that—the other part of the equation—is how the content iscompressed and de-compressed. Better compression techniques—the zen ofknowing what bits of data to pull out to make big data chunkssmaller—make for better quality video while taking up less space onyour hard drive. Basically, the part you need to know is that codecsare the software that make that magic happen.
Standard Standards
• H.261 is not a term you have to worry about, but it's the technology that most video standards and codecswere originally based on. Originating in 1990, it's the first majordigital video compression standard, and like other "H" standards, itwas developed by the International Telecommunication Union. This onewas primarily for teleconferencing over ISDN lines, and as such, itlooks like ass.
• MPEG-1 Part 2 is another oldie, developed by the Movie Picture Experts Groupand approved in 1991. (BTW, the whole "part" thing is because video isjust one "part" of each MPEG standard.) Based quite a bit on H.261, MPEG-1 was designed to take VHS quality videoand squeeze it down to a bit rate of about 1.5Mbps, optimized for CDtransfers. No surprise, it's the standard used for all VCDs (which canplay in most DVD players), but not a standard you would see hangingaround today.
• With MPEG-2 Part 2, approved in 1994, we're finally talking decent vid. Also known as H.262, since it was developed jointly by the ITU-T and ISO, MPEG-2 is an extension of MPEG-1that delivers better resolution and higher bit rates (3-15Mbps forstandard def and 15-30Mbps for HD). It's the video codec used by DVDand digital television, though now it's slowly being replaced by themore efficient MPEG-4, except on DVDs, where it'll ride out that discformat's lifetime.
• H.263 is designed for sending video over crappy connections. So it's used to encode most Flash video and to send video over mobile networks.
• MPEG-4is where we really stand right now. It has a much broader scope thanpast MPEG standards, aiming to tackle both the low end (crappycellphones on a crappy network) and the high end (Blu-ray). It's stilldeveloping, so it's not-so-coincidentally where this whole story gets messier.There are two relevant parts of the MPEG-4 standard for our myopicvideo purposes: Part 2 and Part 10—which is also known as H.264 orAdvanced Video Coding (AVC). To be clear though, even though they'reboth part of the MPEG-4 standard, they're totally different formats. Nevertheless, both are more efficient at compression than past MPEG codecs, delivering better quality using less space.
• Okay, so if you've ever frequented a Torrent site, you've actually watched tons of videos that use MPEG-4 Part 2, though it's not like they would've had a flashing sign telling you so. MPEG-4 Part 2 actually [url=http://74.125.45.132/search?q=cache:2-AcZvq6F8YJ:www.mpegif.org/public/documents/ ... -4+profiles&hl=en&ct=clnk&cd=4&gl=us&client=firefox-a]has different "profiles"[/url]—thetwo that matter being Simple Profile, for low bitrate, low-res stuff,and Advanced Simple Profile. The latter profile is what's used bymovies you would download in formats like DivX or XviD or 3ivx—whichare all codecs that are essentially just differing implementations ofthe MPEG-4 Part 2 standard.
• MPEG-4 Part 10,the other part, was actually co-devopled by MPEG and the ITU-T, so it'salso known—in fact, more commonly known—as H.264. It's more efficientthan MPEG-2 and MPEG-4 Part 2, delivering the same quality video in aslittle as half the space, making it suitable for the low and high-end.Because of this, it's quickly becoming the standardest standard.It's part of the HD DVD and Blu-ray spec, replacing MPEG-2 in digitalTV (like with satellite services and AT&T's U-Verse IPTV) andsupported by pretty much every portable video player on the planet fromthe iPod to the PSP. Apple has a decent, if Kool-Aid flavored, FAQ about H.264.
• VC-1 is essentially a Microsoft developed alternative video codecto H.264 released as a standard by the Society of Motion Picture andTelevision Engineers, though it descends from the same H.26X/MPEGfamily. (It essentially started life as WMV9, but then Microsoft shopped it to the SMPTEto make it an industry standard, and now it is.) It too, is part of themandatory Blu-ray and HD DVD spec, and is the official video codec ofthe Xbox 360. It's pitch is the same as H.264's—trying to deliverbetter quality using less space, like HD video in 6-8Mbps.
Free-Floating Codecs
Okay, so all that stuff up there are industry-wide standard video codecs. On top of all of those, various entities love putting out their own spin on those standards. As we mentioned before, DivX (proprietary) and XviD(open source), for instance, use MPEG-4 Part 2 (more specifically,MPEG-4 ASP) compression, meaning stuff that'll natively play backMPEG-4 ASP will also play back DivX. Like the Xbox 360,for instance. There are a ton of MPEG-4 ASP-based codecs, actually,like FFmpeg, 3ivx and others, but DivX and XviD are the most common.Same deal with H.264: Some well known codecs that use it are Apple'sQuicktime H.264, x264 and Nero Digital. You've also got Windows MediaVideo (WMV) codecs, which are Microsoft's proprietary twists onindustry standards.
Containers aka Wrappers
Alright, well you've probably noticed that none of your video fileshave the extension .h264 or .vc1 or the like. That's because videos arepackaged in containers or wrappersthat stuff things like the audio, navigational info, etc. along withthe video in a single pretty file. Naturally, there are about as manyof them as there are codecs. To be clear, you would take a videoencoded with, say, H.264, and wrap it up as a .mp4 or .avi file.
The majors ones are:
• AVI (Audio Video Interleave) is Windows' standard multimedia container
• MPEG-4 Part 14 (known to you as .mp4) is the standardized container for MPEG-4
• FLV (Flash Video) is the format used to deliver MPEG video through Flash Player
• MOV is Apple's QuickTime container format
• OGG, OGM and OGV are open-standard containers
• MKV (Mastroska) is another open-specification container that you've seen if you've ever downloaded anime
• VOB means DVD Video Object. Guess what? It's DVD's standard container, and what you get when you rip a DVD.
• ASF is a Microsoft format designed for WMV and WMA—files can end in .wmv or .asf
So, in order to play a video file, your setup has to be able to handle both the actual video codec andthe container. It's why you can try to play an AVI file and WindowsMedia Player laughs at you, even though it totally played one a minuteago— the container was no problem, but it didn't have the right codec.Or conversely, even though an iPod could play back an H.264 encodedvideo, if it was wrapped up in MKV, it won't be able to read it.
Okay,my brain hurts. Hopefully this will make yours hurt less when it comesto dealing with pesky videos. If you'd like to do even more homework,Wikipedia, as always, has a more in-depth discussion. And Doom9 is always an amazing resource for all things digital video.
Somethingyou still wanna know? Send any questions about codecs, kitties or padthai (but not RealMedia) to tips@gizmodo.com, with "Giz Explains" inthe subject line.
[Image: ME@Flickr]