From 57f0ec1474bf5c0f0d5f361bd9909381ead9b915 Mon Sep 17 00:00:00 2001
From: Thom Johansen <thomj@rockbox.org>
Date: Sun, 12 Jun 2005 14:03:31 +0000
Subject: Added support for reading LAME header delay and padding fields for
 proper gapless MP3 support.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@6689 a1c6a512-1295-4272-9138-f99709370657
---
 firmware/export/mp3data.h | 10 ++++++----
 firmware/mp3data.c        | 24 +++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/firmware/export/mp3data.h b/firmware/export/mp3data.h
index c031cc20ce..a7f2e3d7f0 100644
--- a/firmware/export/mp3data.h
+++ b/firmware/export/mp3data.h
@@ -47,13 +47,15 @@ struct mp3info {
     long byte_count;  /* File size in bytes */
     long file_time;   /* Length of the whole file in milliseconds */
     int vbr_header_pos;
+    int enc_delay;    /* Encoder delay, fetched from LAME header */
+    int enc_padding;  /* Padded samples added to last frame. LAME header */
 };
 
 /* Xing header information */
-#define VBR_FRAMES_FLAG 0x01
-#define VBR_BYTES_FLAG  0x02
-#define VBR_TOC_FLAG    0x04
-
+#define VBR_FRAMES_FLAG  0x01
+#define VBR_BYTES_FLAG   0x02
+#define VBR_TOC_FLAG     0x04
+#define VBR_QUALITY_FLAG 0x08
 
 unsigned long find_next_frame(int fd, long *offset, long max_offset, unsigned long last_header);
 unsigned long mem_find_next_frame(int startpos, long *offset, long max_offset,
diff --git a/firmware/mp3data.c b/firmware/mp3data.c
index 32b3be4ffc..2b58710715 100644
--- a/firmware/mp3data.c
+++ b/firmware/mp3data.c
@@ -32,6 +32,7 @@
 #include <string.h>
 #include <stdbool.h>
 #include "debug.h"
+#include "logf.h"
 #include "mp3data.h"
 #include "file.h"
 #include "buffer.h"
@@ -379,6 +380,12 @@ int get_mp3file_info(int fd, struct mp3info *info)
         return -1;
 
     memset(info, 0, sizeof(struct mp3info));
+    /* These two are needed for proper LAME gapless MP3 playback */
+    /* TODO: These can be found in a LAME Info header as well, but currently
+       they are only looked for in a Xing header. Xing and Info headers have
+       the exact same format, but Info headers are used for CBR files. */
+    info->enc_delay = -1;
+    info->enc_padding = -1;
     if(!mp3headerinfo(info, header))
         return -2;
 
@@ -448,6 +455,22 @@ int get_mp3file_info(int fd, struct mp3info *info)
         if(vbrheader[7] & VBR_TOC_FLAG) /* Is table-of-contents there? */
         {
             memcpy( info->toc, vbrheader+i, 100 );
+            i += 100;
+        }
+        if (vbrheader[7] & VBR_QUALITY_FLAG)
+        {
+            /* We don't care about this, but need to skip it */
+            i += 4;
+        }
+        i += 21;
+        info->enc_delay = (vbrheader[i] << 4) | (vbrheader[i + 1] >> 4);
+        info->enc_padding = ((vbrheader[i + 1] & 0x0f) << 8) | vbrheader[i + 2];
+        if (!(info->enc_delay >= 0 && info->enc_delay <= 1152 && 
+            info->enc_padding >= 0 && info->enc_padding <= 2*1152))
+        {
+           /* Invalid data */
+           info->enc_delay = -1;
+           info->enc_padding = -1;
         }
     }
 
@@ -488,7 +511,6 @@ int get_mp3file_info(int fd, struct mp3info *info)
                                      vbrheader[12], vbrheader[13]);
         info->frame_count = BYTES2INT(vbrheader[14], vbrheader[15],
                                       vbrheader[16], vbrheader[17]);
- 
         info->file_time = info->frame_count * info->frame_time;
         info->bitrate = info->byte_count * 8 / info->file_time;
 
-- 
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