Compression reduces the size of a file by using complex mathematical equations that remove information from the content that is not necessary for hearing or viewing it. This means that the video, sound, or file you are working with will be quicker to download online, but you will always lose some quality in the process.
There are several software programs, other than Flash, which are made to compress video files in particular. You can use professional solutions such as Discreet Cleaner 6 (Mac) or Discreet Cleaner XL (Windows), or you can use a simple solution such as QuickTime Pro. Sorenson Squeeze, which has features that are created with Flash in mind, can compress videos directly into FLV (Flash Video) or SWF formats.
Other programs, such as Windows Movie Maker 2, allow you to compress video when you export a video project. This ability can be particularly useful if you need to edit video in ways that Flash cannot.
The most important thing you can remember about compression is to always try to avoid recompressing sounds or video after they haves already been compressed. Recompressing material leads to a significant loss in quality.
Codecs are small pieces of software that are used to compress and then decompress files. The file is compressed for placing online and then it is decompressed by the codec again when viewed on the client's computer. Sorenson Video 3, Cinepak, QDesign Music 2 (audio), Mpeg4, and DivX are examples of codecs. If you compress a video using a particular codec, both you and those watching your video would need that codec installed to decompress the video again. Sometimes codecs are already installed into players such as the QuickTime player, but other codecs need to be installed separately by the end user.
Flash uses On2 VP6 codec by default, which is a codec that is specifically for importing video into a Flash document. The codec is built into the Flash Video importer. Flash 8 can also use the Sorensen Spark codec.