From 85914b1843bd89ca94a722cc26e572089dbd0774 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sun, 24 Jun 2018 17:45:13 +0300
Subject: [PATCH] Refactor Mp3Decoder a bit

It's now possible to decode only the header for a frame
---
 source/mp3decoder.cpp | 43 +++++++++++++++++++++++++------------------
 source/mp3decoder.h   |  3 ++-
 2 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/source/mp3decoder.cpp b/source/mp3decoder.cpp
index 00fc918..ec08be7 100644
--- a/source/mp3decoder.cpp
+++ b/source/mp3decoder.cpp
@@ -54,7 +54,9 @@ Mp3Decoder::Mp3Decoder(IO::Seekable &io):
 
 	try
 	{
-		decode_frame();
+		if(!fill_input() || !decode(false))
+			throw runtime_error("no mp3 data");
+
 		format = create_format(2, MAD_NCHANNELS(&priv->frame.header));
 		freq = priv->frame.header.samplerate;
 	}
@@ -98,11 +100,8 @@ unsigned Mp3Decoder::read(char *buf, unsigned len)
 	unsigned pos = 0;
 	while(pos+2*nchan<=len)
 	{
-		if(read_pos>=pcm.length)
-		{
-			if(!decode_frame())
-				break;
-		}
+		if(read_pos>=pcm.length && !decode(true))
+			break;
 
 		for(unsigned i=0; i<nchan; ++i)
 		{
@@ -135,26 +134,34 @@ bool Mp3Decoder::fill_input()
 	return len;
 }
 
-bool Mp3Decoder::decode_frame()
+bool Mp3Decoder::try_decode(bool full)
 {
-	while(1)
+	if(full)
+		return !mad_frame_decode(&priv->frame, &priv->stream);
+	else
+		return !mad_header_decode(&priv->frame.header, &priv->stream);
+}
+
+bool Mp3Decoder::decode(bool full)
+{
+	while(!try_decode(full))
 	{
-		if(!priv->stream.buffer || priv->stream.error==MAD_ERROR_BUFLEN)
+		if(priv->stream.error==MAD_ERROR_BUFLEN)
+		{
 			if(!fill_input())
 				return false;
-
-		if(!mad_frame_decode(&priv->frame, &priv->stream))
-		{
-			mad_synth_frame(&priv->synth, &priv->frame);
-			read_pos = 0;
-			return true;
 		}
-
-		if(priv->stream.error==MAD_ERROR_BUFLEN)
-			continue;
 		else if(!MAD_RECOVERABLE(priv->stream.error))
 			throw mp3_error("mad_frame_decode", priv->stream.error);
 	}
+
+	if(full)
+	{
+		read_pos = 0;
+		mad_synth_frame(&priv->synth, &priv->frame);
+	}
+
+	return true;
 }
 
 } // namespace AL
diff --git a/source/mp3decoder.h b/source/mp3decoder.h
index 06060de..c026081 100644
--- a/source/mp3decoder.h
+++ b/source/mp3decoder.h
@@ -40,7 +40,8 @@ public:
 
 private:
 	bool fill_input();
-	bool decode_frame();
+	bool try_decode(bool);
+	bool decode(bool);
 };
 
 } // namespace AL
-- 
2.43.0