[FFmpeg-devel] [PATCH] avcodec/ac3dec: Check expacc

Michael Niedermayer michael at niedermayer.cc
Thu Nov 3 22:25:40 EET 2016


On Thu, Nov 03, 2016 at 09:18:57PM +0100, Andreas Cadhalpun wrote:
> On 03.11.2016 11:30, Michael Niedermayer wrote:
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavcodec/ac3dec.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
> > index a95c204..499971a 100644
> > --- a/libavcodec/ac3dec.c
> > +++ b/libavcodec/ac3dec.c
> > @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s,
> >      group_size = exp_strategy + (exp_strategy == EXP_D45);
> >      for (grp = 0, i = 0; grp < ngrps; grp++) {
> >          expacc = get_bits(gbc, 7);
> > +        if (expacc >= 125) {
> 
> This is somewhat a magic number, which can be understood from reading section
> "7.1.2 Exponent Strategy" of the ac3 specification, in short:
> Three exponents each represented as number 0-4 are grouped together and
> base-5 encoded, so the maximal correct value is 25*4 + 5*4 + 4 = 124.
> 
> Maybe mention this in the commit message.

added, applied

thx

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

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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