[FFmpeg-devel] [PATCH] avfilter/af_alimiter: fix misbehavior when nb_channels != 2

[David Flater]

This is a friendly reminder.

Cc: Paul B Mahol <onemda at gmail.com>

On 2022-08-14 21:53, David Flater wrote:
> Some code in alimiter assumes that there are 2 channels, resulting in
> clipping if the loudest channel is 3 or above and an out-of-bounds read if
> the input is monophonic.  Fix that in 2 places.
> 
> Signed-off-by: David Flater <dave at flaterco.com>
> ---
>  libavfilter/af_alimiter.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/libavfilter/af_alimiter.c b/libavfilter/af_alimiter.c
> index 622dc66324..c683c4bcf4 100644
> --- a/libavfilter/af_alimiter.c
> +++ b/libavfilter/af_alimiter.c
> @@ -194,10 +194,11 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>              } else {
>                  for (i = s->nextiter; i < s->nextiter + s->nextlen; i++) {
>                      int j = i % buffer_size;
> -                    double ppeak, pdelta;
> +                    double ppeak = 0, pdelta;
>  
> -                    ppeak = fabs(buffer[nextpos[j]]) > fabs(buffer[nextpos[j] + 1]) ?
> -                            fabs(buffer[nextpos[j]]) : fabs(buffer[nextpos[j] + 1]);
> +                    for (c = 0; c < channels; c++) {
> +                        ppeak = FFMAX(ppeak, fabs(buffer[nextpos[j] + c]));
> +                    }
>                      pdelta = (limit / peak - limit / ppeak) / (((buffer_size - nextpos[j] + s->pos) % buffer_size) / channels);
>                      if (pdelta < nextdelta[j]) {
>                          nextdelta[j] = pdelta;
> @@ -241,14 +242,16 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
>                  s->delta = get_rdelta(s, release, inlink->sample_rate,
>                                        peak, limit, s->att, 1);
>                  if (s->nextlen > 1) {
> +                    double ppeak = 0, pdelta;
>                      int pnextpos = nextpos[(s->nextiter + 1) % buffer_size];
> -                    double ppeak = fabs(buffer[pnextpos]) > fabs(buffer[pnextpos + 1]) ?
> -                                                            fabs(buffer[pnextpos]) :
> -                                                            fabs(buffer[pnextpos + 1]);
> -                    double pdelta = (limit / ppeak - s->att) /
> -                                    (((buffer_size + pnextpos -
> -                                    ((s->pos + channels) % buffer_size)) %
> -                                    buffer_size) / channels);
> +
> +                    for (c = 0; c < channels; c++) {
> +                        ppeak = FFMAX(ppeak, fabs(buffer[pnextpos + c]));
> +                    }
> +                    pdelta = (limit / ppeak - s->att) /
> +                             (((buffer_size + pnextpos -
> +                             ((s->pos + channels) % buffer_size)) %
> +                             buffer_size) / channels);
>                      if (pdelta < s->delta)
>                          s->delta = pdelta;
>                  }