Re: [FFmpeg-devel] [PATCH v2 09/13] avfilter/f_ebur128: move true peak calculation out of main loop

[Niklas Haas <ffmpeg@haasn.xyz>]

On Mon, 16 Jun 2025 13:19:57 +0200 Niklas Haas <ffmpeg@haasn.xyz> wrote:
> From: Niklas Haas <git@haasn.dev>
>
> Easier to read, less convoluted, and ~30% faster. Most importantly, this
> avoids repeating the redundant recalculation of the true peak on every single
> sample, by moving the FIND_PEAK() loop out of the main loop. (Note that
> FIND_PEAK() does not depend on the current sample index at all, so there is no
> reason for it to ever be recomputed here)

Fixed the commit message formatting locally.

> ---
>  libavfilter/f_ebur128.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/libavfilter/f_ebur128.c b/libavfilter/f_ebur128.c
> index 2e1eedd855..23092b597f 100644
> --- a/libavfilter/f_ebur128.c
> +++ b/libavfilter/f_ebur128.c
> @@ -668,16 +668,22 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
>                                (const uint8_t **)insamples->data, nb_samples);
>          if (ret < 0)
>              return ret;
> -        for (ch = 0; ch < nb_channels; ch++)
> -            ebur128->true_peaks_per_frame[ch] = 0.0;
> -        for (idx_insample = 0; idx_insample < ret; idx_insample++) {
> -            for (ch = 0; ch < nb_channels; ch++) {
> -                ebur128->true_peaks[ch] = FFMAX(ebur128->true_peaks[ch], fabs(*swr_samples));
> -                ebur128->true_peaks_per_frame[ch] = FFMAX(ebur128->true_peaks_per_frame[ch],
> -                                                          fabs(*swr_samples));
> -                swr_samples++;
> +
> +        double maxpeak = 0.0;
> +        for (int ch = 0; ch < nb_channels; ch++) {
> +            double tp   = ebur128->true_peaks[ch];
> +            double tppf = 0.0;
> +            for (int i = 0; i < ret; i++) {
> +                const double sample = fabs(swr_samples[i * nb_channels]);
> +                tp   = FFMAX(tp,   sample);
> +                tppf = FFMAX(tppf, sample);
>              }
> +            maxpeak = FFMAX(maxpeak, tp);
> +            ebur128->true_peaks[ch] = tp;
> +            ebur128->true_peaks_per_frame[ch] = tppf;
>          }
> +
> +        ebur128->true_peak = DBFS(maxpeak);
>      }
>  #endif
>
> @@ -720,7 +726,6 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *insamples)
>          }
>
>          FIND_PEAK(ebur128->sample_peak, ebur128->sample_peaks, SAMPLES);
> -        FIND_PEAK(ebur128->true_peak,   ebur128->true_peaks,   TRUE);
>
>          /* For integrated loudness, gating blocks are 400ms long with 75%
>           * overlap (see BS.1770-2 p5), so a re-computation is needed each 100ms
> --
> 2.49.0
>
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