Sound Tweak Rpi4

[hestehandler]

This suggests to me the cache need not be very big if size confers no advantage.

I agree, from my observations with this, the larger memory just fills up with tracks that have already been played.  As long as the input buffer is bigger than the single largest file in a collection, it will be big enough.

That is not accurate. Logically the minimum size will be the sum of the size of the two largest tracks you have. While one track is playing from the cache, the next is being loaded into the cache.

But it doesn't look like that's what is happening, it would appear the "next" track is loaded into the input cache at the point that it begins playing so the cache has the currently playing track plus any previously played tracks, there appear to be no future tracks in there.

I just checked the network traffic with vnstat, and it appears you are right. Tracks are loaded as they start playing rather than being pre-loaded. Apologies. The input_cache is rather more crude than I imagined.