From 011c33e91ec56c64e26312cf5cdb60890a84d32e Mon Sep 17 00:00:00 2001
From: Vincent Penquerc'h <vincent.penquerch@collabora.co.uk>
Date: Mon, 14 Nov 2011 15:34:57 +0000
Subject: [PATCH] flacparse: detect when a file lies about fixed block size

If the sample/block number happens to be the same as the block
size, we assume variable block size, and thus counters in samples
in the headers. This can only get us a false positive for a block
size of 1, which is invalid. We can get false negatives more
often though (eg, if not starting at the start of the stream),
but then that's already GIGO.
---
 gst/audioparsers/gstflacparse.c | 12 ++++++++++++
 gst/audioparsers/gstflacparse.h |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/gst/audioparsers/gstflacparse.c b/gst/audioparsers/gstflacparse.c
index 05bfd0e0f1..637319f621 100644
--- a/gst/audioparsers/gstflacparse.c
+++ b/gst/audioparsers/gstflacparse.c
@@ -399,6 +399,8 @@ gst_flac_parse_frame_header_is_valid (GstFlacParse * flacparse,
 
   /* 0 == fixed block size, 1 == variable block size */
   blocking_strategy = gst_bit_reader_get_bits_uint8_unchecked (&reader, 1);
+  if (flacparse->force_variable_block_size)
+    blocking_strategy = 1;
 
   /* block size index, calculation of the real blocksize below */
   block_size = gst_bit_reader_get_bits_uint16_unchecked (&reader, 4);
@@ -532,6 +534,16 @@ gst_flac_parse_frame_header_is_valid (GstFlacParse * flacparse,
   if (actual_crc != expected_crc)
     goto error;
 
+  /* Sanity check sample number against blocking strategy, as it seems
+     some files claim fixed block size but supply sample numbers,
+     rather than block numbers. */
+  if (set && blocking_strategy == 0 && block_size == sample_number) {
+    GST_WARNING_OBJECT (flacparse, "This file claims fixed block size, "
+        "but seems to be lying: assuming variable block size");
+    flacparse->force_variable_block_size = TRUE;
+    blocking_strategy = 1;
+  }
+
   /* 
      The FLAC format documentation says:
      The "blocking strategy" bit determines how to calculate the sample number
diff --git a/gst/audioparsers/gstflacparse.h b/gst/audioparsers/gstflacparse.h
index 1c6db0e581..282755244c 100644
--- a/gst/audioparsers/gstflacparse.h
+++ b/gst/audioparsers/gstflacparse.h
@@ -79,6 +79,8 @@ struct _GstFlacParse {
 
   GList *headers;
   GstBuffer *seektable;
+
+  gboolean force_variable_block_size;
 };
 
 struct _GstFlacParseClass {