[FFmpeg-devel] Re: [PATCH] avfilter/af_afftfilt: fix the overlap buffer size

[Sidd via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20933

On Sun, Nov 16, 2025 at 4:19 PM nots1dd <sid9.karanam@gmail.com> wrote:
>
> From what I understand, we only need to be moving N bytes as window_size
> - s->hop_size after inverse fft to the buffer for overlap. Currently the
> compiler throws a warning regarding possible overflow and this patch
> fixs it.
> ---
>  libavfilter/af_afftfilt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/libavfilter/af_afftfilt.c b/libavfilter/af_afftfilt.c
> index 08cdcae2f7..4fc28c6143 100644
> --- a/libavfilter/af_afftfilt.c
> +++ b/libavfilter/af_afftfilt.c
> @@ -250,6 +250,7 @@ static int filter_channel(AVFilterContext *ctx, void *arg, int jobnr, int nb_job
>  {
>      AFFTFiltContext *s = ctx->priv;
>      const int window_size = s->window_size;
> +    const int hop_size = s->hop_size;
>      const float *window_lut = s->window_func_lut;
>      const float f = sqrtf(1.f - s->overlap);
>      const int channels = s->channels;
> @@ -294,7 +295,7 @@ static int filter_channel(AVFilterContext *ctx, void *arg, int jobnr, int nb_job
>
>          s->itx_fn(s->ifft[ch], fft_out, fft_temp, sizeof(*fft_temp));
>
> -        memmove(buf, buf + s->hop_size, window_size * sizeof(float));
> +        memmove(buf, buf + hop_size, (window_size - hop_size) * sizeof(float));
>          for (int i = 0; i < window_size; i++)
>              buf[i] += fft_out[i].re * window_lut[i] * f;
>      }
> --
> 2.51.0
>
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