Staff Sergeant is usually abbreviated SSgt without the period, in rare cases it may be abbreviated SSG but I don't believe I've ever personally seen it abbreviated S.Sgt
With that being said, in any rank system usually the rank is the one that the 's' is added to to make plural and the qualifier is left alone. For example, the plural of Gunnery Sergeant is Gunnery Sergeants but the plural of Sergeant Major is Sergeants Major (no source for this, just one of those "ooh ahh" facts I learned as a boot in the Marines).
Edit:
Source for usage of "Sergeants" and Sergeants Major":
The sergeants and sergeants major, trained now to receive instant 8 Regimental Sergeant Major respect and obedience, came home to find alien young males – Was That Really Me?
by Ernest Millington
So in practice zeros is preferred in the US and even more so in the UK, though citations for zeroes include such prominent examples as Stephen Hawking's Brief History of Time. (Mr Hawking is British, but the book was first published by an American publishing house.) The oldest citation for zeroes in the BNC is from 1978. The Corpus of Historical American English has six citations that are even older, the oldest one being from 1914.
For all I know, software is uncountable, so it's perfectly fine to say "there is various software". If you don't like how that sounds (I know many people who don't), you can always go with "there are various software packages", "there are various pieces of software" or something like that. An even simpler alternative would be "programs". Depending on the context of your sample sentence, even "video converters" might work, if it's already clear that you are talking about software.
Best Answer
Staff Sergeant is usually abbreviated SSgt without the period, in rare cases it may be abbreviated SSG but I don't believe I've ever personally seen it abbreviated S.Sgt
https://en.wikipedia.org/wiki/Staff_sergeant
With that being said, in any rank system usually the rank is the one that the 's' is added to to make plural and the qualifier is left alone. For example, the plural of Gunnery Sergeant is Gunnery Sergeants but the plural of Sergeant Major is Sergeants Major (no source for this, just one of those "ooh ahh" facts I learned as a boot in the Marines).
Edit: Source for usage of "Sergeants" and Sergeants Major":
Ngram: Sergeant major - Sergeants major.