From 8ac5f63d63b298bb729dedde02e8c50d0efb17f4 Mon Sep 17 00:00:00 2001
From: Robin Haberkorn <robin.haberkorn@googlemail.com>
Date: Tue, 5 Sep 2023 03:33:52 +0300
Subject: libsndfile related classes moved into sndfile-stream.lua

---
 sndfile-stream.lua | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 sndfile-stream.lua

(limited to 'sndfile-stream.lua')

diff --git a/sndfile-stream.lua b/sndfile-stream.lua
new file mode 100644
index 0000000..68ed5cc
--- /dev/null
+++ b/sndfile-stream.lua
@@ -0,0 +1,100 @@
+local sndfile = require "sndfile"
+
+SndfileStream = DeriveClass(Stream)
+
+function SndfileStream:ctor(filename, samplerate, channels, format)
+	-- FIXME: This fails if the file is not at the
+	-- correct sample rate. Need to resample...
+	-- NOTE: samplerate and channels are ignored unless SF_FORMAT_RAW
+	-- files are read.
+	local handle = sndfile:new(filename, "SFM_READ",
+	                           samplerate, channels, format)
+	self.filename = filename
+	self.samplerate = handle.info.samplerate
+	self.channel_no = handle.info.channels
+	self.format = handle.info.format
+	self.frames = tonumber(handle.info.frames)
+	handle:close()
+
+	if self.channel_no > 1 then
+		local cached = self:cache()
+		local streams = {}
+		for i = 0, self.channel_no-1 do
+			streams[i+1] = cached:map(function(frame)
+				return tonumber(frame[i])
+			end)
+		end
+		return MuxStream:new(unpack(streams))
+	end
+end
+
+function SndfileStream:gtick()
+	-- The file is reopened, so each tick has an independent
+	-- read pointer which is important when reusing the stream.
+	-- NOTE: We could do this with a single handle per object but
+	-- by maintaining our own read position and seeking before reading.
+	local handle = sndfile:new(self.filename, "SFM_READ",
+	                           self.samplerate, self.channel_no, self.format)
+
+	-- Make sure that we are still reading the same file;
+	-- at least with the same meta-data.
+	-- Theoretically, the file could have changed since object
+	-- construction.
+	assert(handle.info.channels == self.channel_no and
+	       handle.info.frames == self.frames,
+	       "Sndfile changed")
+
+	if self.channel_no == 1 then
+		local read = handle.read
+
+		return function()
+			return read(handle)
+		end
+	else
+		-- For multi-channel audio files, we generate a stream
+		-- of frame buffers.
+		-- However, the user never sees these since they are translated
+		-- to a MuxStream automatically (see ctor())
+		local readf = handle.readf
+		local frame = sndfile.frame_type(self.channel_no)
+
+		return function()
+			return readf(handle, frame) and frame or nil
+		end
+	end
+end
+
+function SndfileStream:len() return self.frames end
+
+-- TODO: Use a buffer to improve perfomance (e.g. 1024 samples)
+function Stream:save(filename, format)
+	if self:len() == math.huge then
+		error("Cannot save infinite stream")
+	end
+
+	local channels = self.channels
+	local hnd = sndfile:new(filename, "SFM_WRITE",
+	                        samplerate, channels, format)
+
+	local frame_buffer = sndfile.frame_type(channels)
+
+	self:foreach(function(frame)
+		-- NOTE: This should be (hopefully) automatically
+		-- unrolled for single-channel streams
+		-- Otherwise each loop copies an entire frame.
+		-- This should be faster than letting LuaJIT translate
+		-- the frame directly.
+		for i = 1, channels do
+			local sample = tonumber(frame[i])
+			assert(sample ~= nil)
+			frame_buffer[i-1] = sample
+		end
+
+		-- NOTE: Apparently we cannot use hnd:write() if a frame is larger than one sample
+		-- (i.e. multichannel streams)
+		-- FIXME: Check return value
+		hnd:writef(frame_buffer)
+	end)
+
+	hnd:close()
+end
-- 
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