Bidirectional

While many of the settings available under the Advanced Codec tab will simply affect picture quality, the Bidirectional setting can affect compatibility so this is an important one to consider.

Without going into too much detail about how video compression works, you should understand that the output file is basically a mixture of partial images with a few complete pictures sprinkled around (keyframes). DivX will start with a complete picture then progressively apply changes to make the picture move. Every once in a while, a new, complete picture is displayed and the process starts over again.

Turning the Bidirectional setting off, reduces the number of complete pictures that a DivX player has to track while displaying your video. Changing the setting to Adaptive Single Consecutive, makes DivX players remember more pictures at one time.

The catch is, not all players are capable enough to handle Adaptive Single Consecutive encoded videos. Particularly, small devices like phones may have trouble playing those videos. However, any devices that are DivX certified for the Portable profile or better, will be able to handle those videos with no problem.

You certainly want to use Adaptive Single Consecutive if your DivX player can handle it. Most can and it will provide significantly better picture quality in almost every case.

Max Keyframe Interval

Fundamentally, video compression is achieved by not including every frame from the original video. Only a few key frames are included in the compressed video. The DivX player creates the frames in between by incrementally applying the necessary differences. Dr. DivX tries to figure out the best place for keyframes and will try to go as long as possible without using keyframes. This gives the highest compression but it's also a lot of work for the DivX player. The Max Keyframe Interval allows you to limit how long Dr. DivX will go without a keyframe.

If you are experimenting with low-bitrate encoding, you may want to increase the Max Keyframe Interval to improve the over-all quality assuming your player can handle it.

Framerate

The Framerate setting controls how many frames per. second will be displayed while your video is playing. The exact numbers available for you to choose from will be dependent on the framerate of your original video, but you'll usually have two options that amount to full-rate or half-rate. Typically, you'll want the highest framerate possible. However, if you are making videos for small, portable, slow devices like PDAs or cell phones, you may want to drop the framerate to make sure that the player will be able to keep up. The result might not look as smooth but at least it will play.