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C h a p t e r 7 Understanding Audio/Video Technology 73

Understanding Video File Formats

When you’re producing a YouTube video, you have to take into account more than
just resolution and aspect ratio. You also have to choose a video file format, and the
accompanying compression used in that file format.

Understanding Compression and Codecs

Key to all video file formats is the concept of file compression. That’s because raw,
uncompressed video files are extremely large; video information is quite complex
and requires much storage space. Rather than force users to work with unmanage-
ably large files, the video industry adopted the concept of file compression, which
works to reduce the size of the video files.

Each different method of compression is a codec, short for compressor/decompres-
sor. A codec is a system for compressing a large amount of video data into a
smaller, more manageable file. The more efficient the codec, the smaller the result-
ing files.

It isn’t all about size, however. Some codecs do a better job of maintaining video
quality than do others. That is, some compression schemes create videos that are
noticeably inferior to the original; other compression schemes create videos that
look almost identical to the source material. Lossy codecs result in a loss of data and
degradation in audio and video quality, whereas lossless codecs reproduce the
source material with no loss in quality.

Not only are different codecs better or worse at reproducing the source material,
often you have the option of selecting different degrees of compression within a
codec. That is, you can encode the video data at different rates (measured in
kilobytes per second, or kbps). The higher the encoding rate, the better the resulting
quality—and the larger the resulting file. For example, a file encoded at 256kbps
would theoretically have twice the resolution or quality as a file encoded at
128kbps. Which file format and codec you choose represents a compromise
between file size and audio/video quality—with the issue of compatibility thrown
in for good measure.

Comparing File Formats

Codecs are important because different file formats use different forms of compres-
sion—and you have lots of file formats to choose from.

A file format is a particular way of encoding digital information. There are many
different file formats for different uses; for example, Adobe’s PDF file format is used
to create printable documents, Microsoft’s DOC file format is used to create Word