File extensions are notoriously misleading and nowhere is this more true than the AVI file. Many files are renamed using proprietary file extensions such as MP4, DivX or XviD. This is actually a useful practice insofar as it tells you what code was used to compress the file. If you don't have the decompression codec you will not be able to convert the file.

Some codec manufacturers, such as DivX, distribute their decompression codec in two formats: One will decompress the file to play it but you need to buy the pro version to edit or convert the file.

If you're having trouble identifying the codec used to create your AVI file try

SHERLOCK - The Codec Detective

If you are very familiar with computers you can open the source in a binary editor and read the FourCC identifier. The below Web pages may help you match the ID to the name of the codec and find the person or organization that created the codec.

• Microsoft Audio codecs: Registered FourCC Codes and WAVE Formats
• Video codecs: FourCC.org

When converting AVI files to MPEG you should be aware of the height and width resolution of your source versus the resolution of the MPEG target. MPEG-1 has no restrictions on height and width but MPEG-2 is quite specific and your output file might be distorted.

Converting AVI to MPEG-1 (or VCD)

Images below are from a Windows Vista operating system. Other operating systems may appear different.

The Fx MPEG Writer interface requires that you enter the path to the source movie that you wish to convert and to the target movie that will become the converted file.

Clicking the Source button opens a dialog window which displays movies of the type that you select from the drop down. Picking your movie populates the file name in the dialog window, the Movie In text box and, if the automatic naming option is selected, a suggested name for the Movie out.

The load may take some time depending upon the size and complexity of your source movie. Wait until the word Loaded appears in the lower left hand corner before proceeding further.

To convert your moving using the default settings click Start. On the main tab you can also change the source audio, exclude any audio, pop up an audio codec dialog, force the conversion to keep the same number of frames or dither the output to improve low color depth source movies.

You can also fine-tune the MPEG settings by removing the check from the box labeled use MPEG Presets. This will enable the MPEG Settings tab.

When you're ready click the Start button.

Fx MPEG writer will next read the source file video and audio from start to finish. This  may take some time, depending upon the size and complexity of the source.

Once conversion starts progress is shown at the bottom of the window.

When all frames and samples have been read and written to temporary files your new file will be multipelxed.

When the conversion is complete Fx MPEG Writer makes a request to Windows to clean up memory and temporary drive space. The time for this is unpredictable and because Windows provides no feedback during housekeeping, Fx MPEG Writer may appear to be hung. Be patient and wait until the Stop button says Start before closing the program. Try to close it before Windows finishes will produce a "Not Responding" error from Windows and unpredictable results.

Converting to MPEG-2 is essentially the same as MPEG-1. The preset MPEG-2 formats included with Fx MPEG Writer are DVD and SVCD.