When choosing to convert regular video to Flash Video, there are two basic codecs: H.263 codec and VP6 codec. Each has different uses and strengths.

What is H.263?

H.263 is a video codec standard originally designed as a low-bitrate compressed format. It was developed by the ITU-T Video Coding Experts Group (VCEG) in a project ending in 1995/1996 as one member of the H.26x family of video coding standards.

H.263 has since found many applications on the internet: much flash video content (as used on sites such as YouTube, Google Video, MySpace, etc.) is encoded in this format, though many sites now use VP6 encoding.

Sorensen Spark, based on h.263, is available in Flash 6-9. It has a wider area of compatibility than the VP6 codec does. If your video is intended to be watched by the public over the internet, it might not be a bad idea to use the Sorensen codec to encode your video. Because video encoded with the Sorenses codec will play on Flash Player versions 6 and later, it is ideal for reaching the broadest audience.

The FLV file encoded with H.263 codec:

What is flash 8 codec?

With the advent of Flash player 8, a new codec has been created that greatly improved encoding and playback of Flash Video. That codec is On2 VP6 (Same as Flash 8 codec), and features much better compression and image quality than the Sorensen codec. However, using the new codec, the users will only be able to watch video encoded in Flash Player 8 or newer, and playback requires more processing power than previous codecs.

The FLV file encoded with Flash 8 codec:

On the whole:

Flash 8 codec only works with Flash Player 8, so the users may need to upgrade their players prior to viewing their videos. If you absolutely need to make your content compatible with Flash Player 7, then choose H.263 (a.k.a Sorenson Spark), which is a somewhat older (though H.263 still very capable) compression technology. Its files will be larger and of poorer quality, but take less time to produce.

In the end, it is a matter of balancing availability versus file size and quality, so choosing which codec depends on your desired project.