[FFmpeg-devel] [PATCH 1/2] avcodec/dca_parser: Extend DTS core sync word

[Michael Niedermayer]

On Tue, Apr 28, 2015 at 05:45:35PM +0300, foo86 wrote:
> Check extended sync word for 16-bit LE and BE core streams to reduce 
> probability of alias sync detection. Previously sync word extension was
> checked only for 14-bit streams. 
> 
> This is sufficient to make the sample in ticket #4492 parse successfully.
> The proper solution, however, would involve taking extension sub-stream
> length into account by the parser.
> ---
>  libavcodec/dca_parser.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/dca_parser.c b/libavcodec/dca_parser.c
> index 9797760..41658a5 100644
> --- a/libavcodec/dca_parser.c
> +++ b/libavcodec/dca_parser.c
> @@ -38,7 +38,9 @@ typedef struct DCAParseContext {
>  #define IS_MARKER(state, i, buf, buf_size) \
>      ((state == DCA_SYNCWORD_CORE_14B_LE && (i < buf_size - 2) && (buf[i + 1] & 0xF0) == 0xF0 &&  buf[i + 2]         == 0x07) || \
>       (state == DCA_SYNCWORD_CORE_14B_BE && (i < buf_size - 2) &&  buf[i + 1]         == 0x07 && (buf[i + 2] & 0xF0) == 0xF0) || \
> -      state == DCA_SYNCWORD_CORE_LE || state == DCA_SYNCWORD_CORE_BE || state == DCA_SYNCWORD_SUBSTREAM)
> +     (state == DCA_SYNCWORD_CORE_LE     && (i < buf_size - 2) && (buf[i + 2] & 0xFC) == 0xFC) || \
> +     (state == DCA_SYNCWORD_CORE_BE     && (i < buf_size - 1) && (buf[i + 1] & 0xFC) == 0xFC) || \
> +     state == DCA_SYNCWORD_SUBSTREAM)

i dont think this is safe, buf_size could be always 1, a parser
could be feeded by 1 byte only in each call

also testing with a few random dts files this patch causes many
changes like:
is this intended ?

tested with https://samples.mplayerhq.hu/A-codecs/DTS/dts/5.1%2024bit.dts

--- ref2.crc    2015-04-28 19:21:47.619285678 +0200
+++ new2.crc    2015-04-28 19:21:44.187285606 +0200
@@ -56,8 +56,7 @@
 ,      960,     2012, 0x2583fa70
 ,      960,     2012, 0x979ff3f3
 ,      960,     2012, 0xbc32f58f
-,      960,     2012, 0xbef8eb01
-,      960,     2012, 0x9a37115b
+,      960,     4024, 0xc153fc5c
 ,      960,     2012, 0x5625f402
 ,      960,     2012, 0xab29f377
 ,      960,     2012, 0xc528e7ad
@@ -312,8 +311,7 @@
 ,      960,     2012, 0x334da9f1
 ,      960,     2012, 0xbd47b990
 ,      960,     2012, 0x4fa0cd82
-,      960,     2012, 0x3bc2c8cb
-,      960,     2012, 0xa68ccb2b
+,      960,     4024, 0x5a479405
 ,      960,     2012, 0x3c64bf12
 ,      960,     2012, 0xb473bd06
 ,      960,     2012, 0x9b1ac192

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
it to them? Then do not be too eager to deal out death in judgement. For
even the very wise cannot see all ends. -- Gandalf
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