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flacparse: detect when a file lies about fixed block size

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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.
This commit is contained in:
Vincent Penquerc'h 2011-11-14 15:34:57 +00:00
parent 1169bb05af
commit 011c33e91e
2 changed files with 14 additions and 0 deletions
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12
gst/audioparsers/gstflacparse.c
View file

@ -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

2
gst/audioparsers/gstflacparse.h
View file

@ -79,6 +79,8 @@ struct _GstFlacParse {
GList *headers;
GstBuffer *seektable;
gboolean force_variable_block_size;
};
struct _GstFlacParseClass {