Multi-pass encoding
Encode in multiple passes, which is useful for bitrate-based encoding. This can be achieved by putting a semicolon between options for differenc passes, for example:
bitrate=??? pass=1; bitrate=??? pass=2
Multi-threading
For encoders that support multi-threading (using multiple processor cores simultaneously), you can use a special variable which will be replaced by the number of CPU cores.
%(threads)s
If an encoder has the option threads then this would look like: