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codecparsers: h264: fix rbsp_more_data() implementation.

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Account for trailing zero bits when checking for rbsp_more_data().

In particular, fix an hypothetical stream whereby rbsp_more_data()
is called in the following conditions for PPS header: NalReader
reached position 20, 12 bits are remaining and trailing data at
current byte position is c8 00.

rbsp_more_data() used to return TRUE whereas it should obviously
return FALSE because x8 00 represents a valid rbsp_trailing_bits()
structure.

https://bugzilla.gnome.org/show_bug.cgi?id=685890

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>
This commit is contained in:
Gwenole Beauchesne 2012-10-10 16:19:49 +02:00
parent 21b897de2f
commit 80a51a8fab
1 changed files with 28 additions and 19 deletions
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47
gst-libs/gst/codecparsers/nalutils.c
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@ -253,33 +253,42 @@ nal_reader_is_byte_aligned (NalReader * nr)
gboolean
nal_reader_has_more_data (NalReader * nr)
{
guint remaining;
NalReader nr_tmp;
guint remaining, nbits;
guint8 rbsp_stop_one_bit, zero_bits;
remaining = nal_reader_get_remaining (nr);
if (remaining == 0)
return FALSE;
if (remaining <= 8) {
guint8 rbsp_stop_one_bit;
nr_tmp = *nr;
nr = &nr_tmp;
if (!nal_reader_peek_bits_uint8 (nr, &rbsp_stop_one_bit, 1))
/* The spec defines that more_rbsp_data() searches for the last bit
equal to 1, and that it is the rbsp_stop_one_bit. Subsequent bits
until byte boundary is reached shall be zero.
This means that more_rbsp_data() is FALSE if the next bit is 1
and the remaining bits until byte boundary are zero. One way to
be sure that this bit was the very last one, is that every other
bit after we reached byte boundary are also set to zero.
Otherwise, if the next bit is 0 or if there are non-zero bits
afterwards, then then we have more_rbsp_data() */
if (!nal_reader_get_bits_uint8 (nr, &rbsp_stop_one_bit, 1))
return FALSE;
if (rbsp_stop_one_bit == 1) {
guint8 zero_bits;
if (remaining == 1)
return FALSE;
if (!nal_reader_peek_bits_uint8 (nr, &zero_bits, remaining))
return FALSE;
if ((zero_bits - (1 << (remaining - 1))) == 0)
return FALSE;
}
}
if (!rbsp_stop_one_bit)
return TRUE;
nbits = --remaining % 8;
while (remaining > 0) {
if (!nal_reader_get_bits_uint8 (nr, &zero_bits, nbits))
return FALSE;
if (zero_bits != 0)
return TRUE;
remaining -= nbits;
nbits = 8;
}
return FALSE;
}
/*********** end of nal parser ***************/