From d365c5394308740f478fbdfbb23e2c5d972f19f0 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sun, 24 Jun 2018 17:46:39 +0300
Subject: [PATCH] Implement seeking in sound decoders

This also fixes a bug in Mp3Decoder where the input buffer was not cleared
on rewind  so playback didn't immediately restart from the beginning.
---
 source/mp3decoder.cpp | 25 ++++++++++++++++++++++++-
 source/mp3decoder.h   |  2 +-
 source/oggdecoder.cpp |  5 +++--
 source/oggdecoder.h   |  2 +-
 source/sounddecoder.h |  3 ++-
 5 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/source/mp3decoder.cpp b/source/mp3decoder.cpp
index ec08be7..34604e3 100644
--- a/source/mp3decoder.cpp
+++ b/source/mp3decoder.cpp
@@ -87,9 +87,32 @@ bool Mp3Decoder::detect(const string &sig)
 	return !sig.compare(0, sizeof(id3_sig), id3_sig);
 }
 
-void Mp3Decoder::rewind()
+void Mp3Decoder::seek(unsigned pos)
 {
+	unsigned unit = get_unit_size(format);
+	pos /= unit;
+
 	in.seek(0, IO::S_BEG);
+	mad_stream_buffer(&priv->stream, 0, 0);
+	fill_input();
+	if(!pos)
+	{
+		priv->synth.pcm.length = 0;
+		return;
+	}
+
+	while(decode(false))
+	{
+		unsigned frame_len = 32*MAD_NSBSAMPLES(&priv->frame.header);
+		if(frame_len>pos)
+		{
+			decode(true);
+			read_pos = pos;
+			break;
+		}
+
+		pos -= frame_len;
+	}
 }
 
 unsigned Mp3Decoder::read(char *buf, unsigned len)
diff --git a/source/mp3decoder.h b/source/mp3decoder.h
index c026081..201d68f 100644
--- a/source/mp3decoder.h
+++ b/source/mp3decoder.h
@@ -35,7 +35,7 @@ public:
 
 	static bool detect(const std::string &);
 
-	virtual void rewind();
+	virtual void seek(unsigned);
 	virtual unsigned read(char *, unsigned);
 
 private:
diff --git a/source/oggdecoder.cpp b/source/oggdecoder.cpp
index 78a2b5a..cd2def8 100644
--- a/source/oggdecoder.cpp
+++ b/source/oggdecoder.cpp
@@ -109,9 +109,10 @@ bool OggDecoder::detect(const std::string &sig)
 	return !sig.compare(0, sizeof(ogg_sig), ogg_sig);
 }
 
-void OggDecoder::rewind()
+void OggDecoder::seek(unsigned pos)
 {
-	ov_pcm_seek(&priv->ovfile, 0);
+	pos /= get_unit_size(format);
+	ov_pcm_seek(&priv->ovfile, pos);
 }
 
 unsigned OggDecoder::read(char *buf, unsigned len)
diff --git a/source/oggdecoder.h b/source/oggdecoder.h
index aab8f5c..3bf33b8 100644
--- a/source/oggdecoder.h
+++ b/source/oggdecoder.h
@@ -31,7 +31,7 @@ public:
 
 	static bool detect(const std::string &);
 
-	virtual void rewind();
+	virtual void seek(unsigned);
 	virtual unsigned read(char *, unsigned);
 };
 
diff --git a/source/sounddecoder.h b/source/sounddecoder.h
index ee5b07d..37fddac 100644
--- a/source/sounddecoder.h
+++ b/source/sounddecoder.h
@@ -37,7 +37,8 @@ public:
 	static SoundDecoder *open_file(const std::string &);
 	static SoundDecoder *open_io(IO::Seekable &);
 
-	virtual void rewind() = 0;
+	virtual void rewind() { seek(0); }
+	virtual void seek(unsigned) = 0;
 	virtual unsigned read(char *, unsigned) = 0;
 	bool eof() const { return eof_flag; }
 
-- 
2.43.0