[FFmpeg-devel] [PATCH 2/2] avcodec/wma: handle run_level_decode error

[Olivier Crête]

On Thu, 2021-08-26 at 12:33 +0200, Michael Niedermayer wrote:
> On Tue, Aug 24, 2021 at 09:43:43AM -0400, Olivier Crête wrote:
> > From: Stéphane Cerveau <scerveau at collabora.com>
> > 
> > Consider data as invalid if ff_wma_run_level_decode
> > gets out with an error.
> > 
> > It avoids an unpleasant sound distorsion.
> > 
> > See http://trac.ffmpeg.org/ticket/9358
> > ---
> >  libavcodec/wmadec.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> > 
> > diff --git a/libavcodec/wmadec.c b/libavcodec/wmadec.c
> > index d627bbe50e..d43fe239ce 100644
> > --- a/libavcodec/wmadec.c
> > +++ b/libavcodec/wmadec.c
> > @@ -601,15 +601,18 @@ static int wma_decode_block(WMACodecContext *s)
> >          if (s->channel_coded[ch]) {
> >              int tindex;
> >              WMACoef *ptr = &s->coefs1[ch][0];
> > +            int ret;
> >  
> >              /* special VLC tables are used for ms stereo because
> >               * there is potentially less energy there */
> >              tindex = (ch == 1 && s->ms_stereo);
> >              memset(ptr, 0, s->block_len * sizeof(WMACoef));
> > -            ff_wma_run_level_decode(s->avctx, &s->gb, &s->coef_vlc[tindex],
> > -                                    s->level_table[tindex], s->run_table[tindex],
> > -                                    0, ptr, 0, nb_coefs[ch],
> > -                                    s->block_len, s->frame_len_bits, coef_nb_bits);
> > +            ret = ff_wma_run_level_decode(s->avctx, &s->gb, &s->coef_vlc[tindex],
> > +                                          s->level_table[tindex], s->run_table[tindex],
> > +                                          0, ptr, 0, nb_coefs[ch],
> > +                                          s->block_len, s->frame_len_bits, coef_nb_bits);
> > +	    if (ret < 0)
> > +                return ret;
> >          }
> >          if (s->version == 1 && s->avctx->channels >= 2)
> >              align_get_bits(&s->gb);
> 
> Does this just discard the packet or replace by silence ?
> if it discards it, it can cause problems with av-sync

It just discards it, but it seems that the Microsoft implementation has
the same behaviour, so I think it's better to be bug compatible with
them.

-- 
Olivier Crête
olivier.crete at collabora.com