What are the reaction products of sulfur and potassium nitrate? YouTube shows videos of dropping a piece of elemental sulfur into molten potassium nitrate and applying additional heat to accelerate the process. A white precipitate falls out to the bottom. There is never any mention as to what this material is. An internet search yields not a clue. Sulfur dioxide is obviously evolved, but KNO doesn't seem to exist if one relies on an internet search.
There are at least two videos (first and second) showing the reaction between sulfur and potassium nitrate. For the chemicals:

\begin{array}{cc}
\rm Species&amp;\rm Melting~point\\\hline
\rm Sulfur &amp;  \rm 115~^\circ C     \\
\rm Potassium~nitrate &amp; \rm 334~^\circ C
\end{array}

It isn't clear if nitrogen, some nitrogen oxides, or both would be produced. My guess is that it would depend on particle size, mixing and so forth, thus that a mixture of nitrogen oxides would be very likely. Also the test tube starts with a tiny amount of oxygen gas from the air. One possible balanced reaction would be:

$$\ce{4KNO3 + 5S -&gt; 2K2O + 5SO2_{(g)} + 2N2_{(g)}}$$

Looking at the products of black powder burning $\ce{K2SO4}$ and $\ce{K2S}$ can also be formed.