fixed SubStream of cached streams

* in particular: SndfileStream(...):sub(...) for multi-channel audio files.
* The fix is more of a workaround just like the initial skipping of samples by sub()
  is a workaround.
  I couldn't yet think of a way how to seek in streams elegantly.

2 files changed, 11 insertions, 7 deletions

diff --git a/TODO b/TODO
index c157b61..d49a831 100644
--- a/TODO
+++ b/TODO
@@ -3,9 +3,6 @@
 * Stream:foreach() cannot be interrupted
   Perhaps C core should export an interrupted variable that we can check from Lua.
   For Stream:play() this is solved differently.
-* SndfileStream(...):sub(...) does not work for multi-channel audio files.
-  The reason is that SubStream ticks in gtick() to seek in the source stream
-  which cannot work in cached streams (SndfileStream:ctor() caches for multi-channel streams).
 
 # Features
 
diff --git a/applause.lua b/applause.lua
index 2d86aa6..cac9704 100644
--- a/applause.lua
+++ b/applause.lua
@@ -1707,12 +1707,19 @@ function SubStream:gtick()
 	-- Perhaps ask stream to skip the first self.i-1 samples
 	-- Either gtick() could take an argument or introduce an
 	-- overwritable gtick_seek(). Problem as always is that
-	-- this would have to chain to substreams.
+	-- this would have to chain to substreams and its now always
+	-- obvious how to pass it on (e.g. to MapStream...).
 	-- Perhaps, it would be wiser to let this be handled by
 	-- an optimizer stage that resolves Stream:sub()-calls.
-	-- @fixme Actually, this is plain wrong and does not work
-	-- if self.stream is cached.
-	for _ = 1, self.i-1 do tick() end
+	for _ = 1, self.i-1 do
+		tick()
+		-- self.stream might be cached (somewhere down the line).
+		-- Therefore it is essential to clear the cache in order to progress
+		-- the stream.
+		-- This however might clear more than necessary,
+		-- resulting in superfluous recalculations.
+		table.clear(sampleCache)
+	end
 
 	local i = self.i