Here you can find a collection of usage examples.
transcode -i sourcevideo -p sourceaudio -x vmod[,amod] \
-o destvideo -y vmod[,amod] \
-J filter ...
The -i option specifies the filename of the source video. If the video file contains no audio stream, it can be read from a separate file using the -p option. The output file name is given with the -o option.
The -x option sets the video[,audio] import modules. If omitted, transcode will probe for appropriate import modules. The same aplies for the -y option, but for export modules and if omitted, transcode will encode to the null module.
There are many other command line options, such as the -J option for filter plugins.