From a19fe100cbebec4ffda1eead0a06a5d6c24a2ef2 Mon Sep 17 00:00:00 2001
From: Arthur Taylor <art@ified.ca>
Date: Mon, 12 Dec 2022 14:10:08 -0800
Subject: [PATCH] sndfile: Identify 'naked' MPEG streams last, even after
 rforks (issue 830)

---
 src/sndfile.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/sndfile.c b/src/sndfile.c
index 21975f65..397740f0 100644
--- a/src/sndfile.c
+++ b/src/sndfile.c
@@ -2771,6 +2771,17 @@ format_from_extension (SF_PRIVATE *psf)
 	return format ;
 } /* format_from_extension */
 
+static int
+identify_mpeg (uint32_t marker)
+{	if ((marker & MAKE_MARKER (0xFF, 0xE0, 0, 0)) == MAKE_MARKER (0xFF, 0xE0, 0, 0) && /* Frame sync */
+		(marker & MAKE_MARKER (0, 0x18, 0, 0)) != MAKE_MARKER (0, 0x08, 0, 0) && /* Valid MPEG version */
+		(marker & MAKE_MARKER (0, 0x06, 0, 0)) != MAKE_MARKER (0, 0, 0, 0) && /* Valid layer description */
+		(marker & MAKE_MARKER (0, 0, 0xF0, 0)) != MAKE_MARKER (0, 0, 0xF0, 0) && /* Valid bitrate */
+		(marker & MAKE_MARKER (0, 0, 0x0C, 0)) != MAKE_MARKER (0, 0, 0x0C, 0)) /* Valid samplerate */
+		return SF_FORMAT_MPEG ;
+	return 0 ;
+} /* identify_mpeg */
+
 static int
 guess_file_type (SF_PRIVATE *psf)
 {	uint32_t buffer [3], format ;
@@ -2872,13 +2883,6 @@ retry:
 	if (buffer [0] == MAKE_MARKER ('R', 'F', '6', '4') && buffer [2] == MAKE_MARKER ('W', 'A', 'V', 'E'))
 		return SF_FORMAT_RF64 ;
 
-	if ((buffer [0] & MAKE_MARKER (0xFF, 0xE0, 0, 0)) == MAKE_MARKER (0xFF, 0xE0, 0, 0) && /* Frame sync */
-		(buffer [0] & MAKE_MARKER (0, 0x18, 0, 0)) != MAKE_MARKER (0, 0x08, 0, 0) && /* Valid MPEG version */
-		(buffer [0] & MAKE_MARKER (0, 0x06, 0, 0)) != MAKE_MARKER (0, 0, 0, 0) && /* Valid layer description */
-		(buffer [0] & MAKE_MARKER (0, 0, 0xF0, 0)) != MAKE_MARKER (0, 0, 0xF0, 0) && /* Valid bitrate */
-		(buffer [0] & MAKE_MARKER (0, 0, 0x0C, 0)) != MAKE_MARKER (0, 0, 0x0C, 0)) /* Valid samplerate */
-		return SF_FORMAT_MPEG ;
-
 	if (buffer [0] == MAKE_MARKER ('I', 'D', '3', 2) || buffer [0] == MAKE_MARKER ('I', 'D', '3', 3)
 			|| buffer [0] == MAKE_MARKER ('I', 'D', '3', 4))
 	{	psf_log_printf (psf, "Found 'ID3' marker.\n") ;
@@ -2887,6 +2891,10 @@ retry:
 		return 0 ;
 		} ;
 
+	/* ID3v2 tags + MPEG */
+	if (psf->id3_header.len > 0 && (format = identify_mpeg (buffer [0])) != 0)
+		return format ;
+
 	/* Turtle Beach SMP 16-bit */
 	if (buffer [0] == MAKE_MARKER ('S', 'O', 'U', 'N') && buffer [1] == MAKE_MARKER ('D', ' ', 'S', 'A'))
 		return 0 ;
@@ -2898,10 +2906,16 @@ retry:
 	if (buffer [0] == MAKE_MARKER ('a', 'j', 'k', 'g'))
 		return 0 /*-SF_FORMAT_SHN-*/ ;
 
-	/* This must be the last one. */
+	/* This must be (almost) the last one. */
 	if (psf->filelength > 0 && (format = try_resource_fork (psf)) != 0)
 		return format ;
 
+	/* MPEG with no ID3v2 tags. Only have the MPEG sync header for
+	 * identification and it is quite brief, and prone to false positives.
+	 * Check for this last, even after resource forks. */
+	if (psf->id3_header.len == 0 && (format = identify_mpeg (buffer [0])) != 0)
+		return format ;
+
 	return 0 ;
 } /* guess_file_type */