Previous Image « » Next Image Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge

Formats and Codecs

With the continuing evolution of digital video and the advent of consumer-accessible high-definition video, the landscape has changed. New formats have come to light, and, with them, new codecs are now in fairly widespread use.

Say What?

A codec is defined as a compressor/decompressor, or a piece of hardware or software that compresses a data stream into a specific format for recording or decompresses the data from that same format for playback. In this context, we'll be discussing codecs for video and audio, although there are also codecs for compressing still images and computer files used from day to day.

We've provided handy-dandy comparison tables of some of the most common formats you'll run across in your days of video production. In it, we include the name of the codec, its developer, the type (whether lossy, lossless or uncompressed) and the typical use for it. We hope it helps you follow along as you read.

Why Should I Care?

The choice of which codec you use for a certain purpose may be a function of how much disk space you have on hand or what your customer might be asking for you to deliver. In these cases, the choice is easier. But if you have a choice or want to be prepared to make a case for using a different codec, we hope to arm you with the information you need.

Codecs can be lumped into several categories. One of the most-used means of comparison for codecs is whether it is lossless or lossy. Lossless compression packs the data in such a way that you preserve every single bit of it, so when you decompress the file, the original file is unscathed. A typical lossy compression scheme, on the other hand, discards data that a typical human wouldn't notice was missing in order to save space. You could also store data in an uncompressed format that you haven't compressed at all - this is the easiest format to process, but, of course, it also takes up the largest amount of data.

Video Codecs

The codec most video producers know best is DV, which is unique in that its compression is particularly gentle (well, processing-wise, anyway). Technically, the reason any computer editing DV can perform editing operations so quickly is that all compression on DV is performed intra-frame, so each frame stands alone. You can perform any cut cleanly, and dissolves take a minimum of processor power to execute. The most common form of DV operates at 25Mbps and is restricted to standard-definition video, but Panasonic's DVCPRO HD (which uses four DV codecs operating in parallel) is worth mentioning as the most accessible high-definition codec that also performs intra-frame compression.

There are a couple of other major codecs used for both acquisition and distribution. The best-known of these is currently MPEG-2. MPEG-2 has become a popular distribution format for its relatively low-bitrate requirements. It is the most common format in such applications as DVD, DBS, digital cable and both of the new high-def disc formats. The other one is H.264/AVC, which is used by AVCHD and both Blu-ray Disc and HD DVD, which is approximately twice as efficient as MPEG-2 but requires significantly more processor power to play back and is supported by only a very small number of editing programs.

Distribution-only codecs include Windows Media and RealVideo. These codecs feature tremendous efficiency, since they are designed for streaming the highest-quality video possible over the finite amount of available bandwidth on the internet - the downside is that you generally are not able to edit them at all.

Another drawback when it comes to compression is that, if you make an edit on a compressed file and then recompress it, the quality may not always be preserved. Some editing programs are able to work with MPEG-2 video clips at I-frame level, so if recompression is necessary, they can do this intelligently to preserve the quality and increase the speed of the render. If the extent of your editing was simple cuts, you might find that a DVD- or hard drive-based camcorder might work just fine for your needs, when paired with an editing program that performs I-frame level editing.

As far as video goes, there are ways to store video without using compression. You'll have to get out your credit card to use any of them, though. Any solution for using uncompressed video requires extremely high bandwidth for storage. This would be one of the times where you'd want to use a RAID 0 for storage (to maximize throughput).

To succinctly summarize this discussion, keep the following in mind. In general, the degree of compression in use determines how difficult the footage will be to edit. The considerations you have to make in finding the best balance include amount of disk space available, processing power available, the amount of bandwidth available (if streaming) or the number of bits available (if authoring to disc).