The nsf format is for 2a03 only; expansions are accepted in the nsfplus format.
Accepted file format
A common beginner's mistake is to submit a FTM (FamiTracker Module) to a NSF compo instead of an NSF file (don't do this!).
Playback (for voting)
Examples of tools that can play .NSF files include:
- VirtuaNSF (version 220.127.116.11 is recommended)
There is a more comprehensive list with compatibility info here.
Render to MP3
Both NSFPlay and VirtuaNSF can render .wav files from .nsf files; note that in some cases, such as when a song is longer than five minutes or loops forever, the output length will need to be specified and/or the resulting file will need to be trimmed. After rendering to .wav, a sound editing tool such as Audacity can be used to normalize the sound file, add a fade out to a looping track, and convert the (minimally) edited song to an .mp3.