From the Windows Start menu, point to Programs, and then click Command Prompt.
In Command Prompt, locate the directory that contains the input source file, and enter the following command (substituting the names of your .asf files):
ASFChop -infilename.asf -outfilename.asf
Append the desired options after the -out option, such as -duration, -end, and -script. Then press enter.
The -out option is optional. If you do not specify this option, ASFChop creates an output file with the same name as the input file and appends the .asf extension.