[PATCH] Add support for VBR files without Xing headers

[Xavier Duret]

This patch adds support for VBR files without Xing headers. I have a
few files for which this patch does not work because the first MPEG
frame is not where it is supposed to be. The patch has to be applied
after the set of patches that I sent previously. List of changes:
- Fix a couple of typos.
- Fix the calculation of the frame length.
- Tidy up nextFrameOffset method.
- Add support for VBR files without Xing headers.

diff -ruN taglib.old/taglib/mpeg/mpegheader.cpp
taglib/taglib/mpeg/mpegheader.cpp
--- taglib.old/taglib/mpeg/mpegheader.cpp       2007-01-17
16:01:31.000000000 +0100
+++ taglib/taglib/mpeg/mpegheader.cpp   2007-01-22 16:30:17.000000000 +0100
@@ -153,7 +153,7 @@
 void MPEG::Header::parse(const ByteVector &data)
 {
   if(data.size() < 4 || uchar(data[0]) != 0xff) {
-    debug("MPEG::Header::parse() -- First byte did not mactch MPEG synch.");
+    debug("MPEG::Header::parse() -- First byte did not match MPEG synch.");
     return;
   }

@@ -162,7 +162,7 @@
   // Check for the second byte's part of the MPEG synch

   if(!flags[23] || !flags[22] || !flags[21]) {
-    debug("MPEG::Header::parse() -- Second byte did not mactch MPEG synch.");
+    debug("MPEG::Header::parse() -- Second byte did not match MPEG synch.");
     return;
   }

@@ -242,11 +242,10 @@
   d->isPadded = flags[9];

   // Calculate the frame length
-
   if(d->layer == 1)
-    d->frameLength = 24000 * 2 * d->bitrate / d->sampleRate + int(d->isPadded);
+    d->frameLength = (12 * d->bitrate * 1000 / d->sampleRate +
int(d->isPadded)) * 4;
   else
-    d->frameLength = 72000 * d->bitrate / d->sampleRate + int(d->isPadded);
+    d->frameLength = 144 * d->bitrate * 1000 / d->sampleRate +
int(d->isPadded);

   // Now that we're done parsing, set this to be a valid frame.

diff -ruN taglib.old/taglib/mpeg/mpegfile.cpp taglib/taglib/mpeg/mpegfile.cpp
--- taglib.old/taglib/mpeg/mpegfile.cpp 2007-01-22 17:44:04.000000000 +0100
+++ taglib/taglib/mpeg/mpegfile.cpp     2007-01-22 17:44:21.000000000 +0100
@@ -447,7 +447,7 @@
 {
   // TODO: This will miss syncs spanning buffer read boundaries.

-  ByteVector buffer = readBlock(bufferSize());
+  ByteVector buffer(bufferSize(),0);

   while(buffer.size() > 0) {
     seek(position);
diff -ruN taglib.old/taglib/mpeg/mpegproperties.cpp
taglib/taglib/mpeg/mpegproperties.cpp
--- taglib.old/taglib/mpeg/mpegproperties.cpp   2007-01-22
17:56:06.000000000 +0100
+++ taglib/taglib/mpeg/mpegproperties.cpp       2007-01-22
17:12:59.000000000 +0100
@@ -225,13 +225,48 @@

     // TODO: Make this more robust with audio property detection for
VBR without a
     // Xing header.
+    long position = first;
+    uint nSamples = 0;
+    uint nFrames = 0;
+    int bitRate = 0;
+    bool cbr = true;
+    d->file->seek(position);
+    while (position < d->file->length()) {
+      Header currentHeader(d->file->readBlock(4));
+      if (currentHeader.isValid()) {
+        position += currentHeader.frameLength();
+        nSamples += (currentHeader.layer() > 1) ? 1152 : 384;
+        d->file->seek(position);
+
+        // Assume that if a file has a constant bit rate for more
than 100 frames
+        // then it is CBR and there is no point in parsing it complely.
+        if (bitRate == 0)
+          bitRate = currentHeader.bitrate();
+        else {
+          if (cbr && (bitRate != currentHeader.bitrate())) {
+            cbr = false;
+            bitRate = currentHeader.bitrate();
+          }
+        }
+        nFrames += 1;
+        if (cbr && nFrames > 100)
+          break;

-    if(firstHeader.frameLength() > 0 && firstHeader.bitrate() > 0) {
-      int frames = (last - first) / firstHeader.frameLength() + 1;
+      } else
+        break;
+    }

-      d->length = int(float(firstHeader.frameLength() * frames) /
-                      float(firstHeader.bitrate() * 125) + 0.5);
-      d->bitrate = firstHeader.bitrate();
+    if (position >= d->file->length()) {
+      d->length = nSamples / firstHeader.sampleRate();
+      d->bitrate = d->length > 0 ? (position - first) / d->length / 1000 : 0;
+    } else {
+      if(firstHeader.frameLength() > 0 && firstHeader.bitrate() > 0) {
+        int frames = (last - first) / firstHeader.frameLength() + 1;
+
+        d->length = int(float(firstHeader.frameLength() * frames) /
+                        float(firstHeader.bitrate() * 125) + 0.5);
+        d->bitrate = firstHeader.bitrate();
+      }
     }
   }