Mo' action Mo' bytes

Codecs are a seemingly complicated concept, so I;m going to try to make it as easy and painful as possible because it's good to know this kind of stuff. I got lots of my information from this video: 
How Codecs Work - Tutorial from David Kong on Vimeo.
It's by a respected contributor on a popular film tutorial website. Here's the breakdown.

First of all:
It understand codecs, you need to understand the difference between codecs and containers. Containers are files like .mov and .avi, they store codecs like h.264 and DNxHD.

Within the category of codecs there are several kinds. There are capture codecs that come in formats like h.264. When shooting, you want as much info possible. There are also editing codecs in formats like DNxhD, in which you would want no temporal compression. From there  you would go onto delivery and archival codecs. I know that this is all still super confusing with new words and concepts, so I'm going to try to clear up the confusion by going through this one chunk at a time.

Bit Depth
Bit depth is the number of values between light and dark. A high bit depth is a super smooth image, a low bit depth is a more choppy image like in pop art. 8-bit means that there is 256 possible values for red yellow and green, so more color.

Chroma Subsampling
Lets say you have four yards in a square. All of the residents of these yards want to use the same landscaper because it would save money, so they all chip in a hire the bottom left yard's landscaper. Now all tho their lawns look like the yard on the bottom left. That would be a 4:2:0 ratio. On the other end of the spectrum there is a 4:4:4 ratio where all pixels maintain their color. Chroma subsampling is minimizing the amount of space that color takes up.

Spatial Compression
This is another way to shrink a file size. This algorithm takes blocks of an image that are the same color and save it as one color. Sometimes this is can be add a "blocky" look to your image.

Temporal Compression
This is a inter frame technique which saves space over a long GOP (Group of pictures) as opposed to all all of the terms we have been using. Chroma Subsampling and Spatial Compression are intra frame techniques so all of the space saving done inside a single frame. Temporal Compression is when the background of several frames are the same and only the difference is saves. This helps with storage because you don't need to restore the image.

Lossless vs Lossy
Lossless means you don't lose any data. They are usually files types like .zip and .rar. Lossy means you are losing info. Most stuff is lossy. But this isn't a bad thing. It just means you are saving more storage.

Bit Rate
Bit rate is essentially how much data a codec uses. Usually it is measured in kilobits/megabits per second, or kbpm/mbps. This is not to confused it megabytes. Here are the conversion rates. 1 Byte = 8 bits. 1000 bits= 1 kilobit. 1,000,000 bits= 1 megabit. The more action you have in your footage, the more bits you need.


So that's pretty much it. Hope this helped with your understanding of Codecs.