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Video codecs: What to know, how they work, and what to use.

What are codecs? Codecs refer to how a video is compressed, and there are two types of codecs: Lossy, and Lossless. First off, Lossless codecs are codecs which don't degrade the image at all. We typically refer to them as uncompressed and/or raw, uncompressed has no compression at all and has huge file sizes. RAW on the otherhand can be compressed or uncompressed, to put it very roughly and simply; RAW packages the video and allows for some compression, but many of those as well are considered lossless, even if it does degrade the image it's considered very neary inperceptible. So if you're using anything labeled uncompressed or RAW, you're getting the good stuff.

Now for the lossy guys, which are the bulk of this quick tip. To understand lossy codecs, let's go through thier basic settings:

Bitrates are the central control, they are referred to in numbers: lower numbers means higher compression which leads to smaller file sizes and worse quality, and higher numbers mean less compression for better quality with larger file sizes. this is the same for any codec. 

But here's the trick: a bitrate of say 10 for one codec can be entirely different for another codec, which is what we called the codec's efficiency. another thing to keep in mind, is what resolution you're using, because a bitrate of say 2 might be good for standard definition video with a certain codec, but if you keep that bitrate and up the resolution, you'll get terrible results. When you're adding pixels, you need to add more data to maintain quality. Presets in your edit system will give you a very good idea of what settings are good for each codec, i usually give it a 20% or so bump in bitrate for good measure on top of whatever the preset has.

Now for some name calling, but in a good way. The biggest buzz word in codec world today is h.264, which is a great efficient codec, but it's also an absurd shape shifter, see because you also know it by several other names. avc intra, mpeg4 avccam, and probably a few others. 

But When you come right down to it, all of these are actually mpeg-4 level 10, now not that you really need to know that, but understand the reason for all this name changing is that mpeg codecs are absurdly customizable and tunable, so each name means a company has made thier own recipe. And just as it is with food, each recipe can either be delicious, or just mildly satisfying. Now that we cleared that up, suffice it to say you don't need to mess with the depths of settings to get a good image, just stick with the basics and try different bit rates to see what's good for you.

And just to name a few other codecs, there is the older but still great mpeg-2, which has been the codec you have watched for years on every single dvd you've ever owned. It has also shape shifted into HDV, which consequently is not seen much anymore because it's a tape based codec. Then we have panasonic's own dvcpro codec, which is great, very good in editing, at the expense of fairly high recording bit rates. 

Then there's Apple's prores which is also very high in bitrate but that also means its darn close to being lossless even though it's a lossy codec. Then there's WMV, DV, HBO, TMZ, it doesn't matter that there's tons of codecs out there, just what works for your needs, which if that's websites, you'll mostly be using h.264. if DVD delivery, mpeg2, if bluray, likely h.264 again. Codecs like mpeg2 and h.264 can be aquisition(capture) formats, and delivery formats, and what's in the middle that's missing? Editing! Yes, although you can do it, it's not ideal to edit h.264, mpeg2, or any other Long GOP codec, because a GOP(group of pictures) means that the codec uses key frames to then base its compression for the next Group of Pictures. So when you cut your video, your cutting that series apart, and making the computer do more work. It also makes grading(coloring) your video more limited. I'll mention though that there are Non GOP versions of h.264 such as AVC-Intra, which are much better for editing.

This is long enough as it is but there is one last piece i can't leave you without, and that's file extensions, such as .wmv, .mpg, .mp4, yea those. These are called containers, and they contain codecs, and the only thing you need to understand about these are that there are containers which are single codec containers, which means they only represent one codec, and then there are containers which can contain any number of different codecs, just not at the same time. The primary multi purpose codecs are .mov and .avi, so if someone tells you to give them an mov or an avi, they just told you to give them one of several dozen different codecs. So what you need to do, is ask for some specifics. Because if you give them any random codec, chances are they won't be able to play it, and they'll blame you. 

A quick word on delivery formats, say if you need to send files to a distribution company, what do they want? We'll, they should tell you, but i know from experience they may just tell you to give them a .avi, or a .mov, and if that aint the definition of vague.... 

The key here is to ask questions, ask if you can send a huffyuv or Lagarith, which are lossless, very high bitrate codecs that will take up alot of space, but you know it'll be pristine. If they want a lossy codec like mpeg2 or h.264, just be sure to use the highest bitrate possible and match the rest of the render settings to how the video was shot. 

Added on 2011-07-13 by
Darren Levine

Darren Levine

Stimulus Video

DP/Videographer, Video/Film Editor
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