SDL: Add comment to audio clipping (see bug #4104)

SDL Commits
1 
From b649314d627a77f25315e49cd29e43ec6fe12e63 Mon Sep 17 00:00:00 2001
From: Sylvain <[EMAIL REDACTED]>
Date: Mon, 15 Nov 2021 13:43:40 +0100
Subject: [PATCH] Add comment to audio clipping (see bug #4104)

---
 src/audio/SDL_audiocvt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index f0cb7e6e40..0b5317cde3 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -456,6 +456,7 @@ SDL_ConvertStereoTo51(SDL_AudioCVT * cvt, SDL_AudioFormat format)
         lf = src[0];
         rf = src[1];
         ce = (lf + rf) * 0.5f;
+        /* Constant 0.571f is approx 4/7 not to saturate */
         dst[0] = 0.571f * (lf + (lf - 0.5f * ce));  /* FL */
         dst[1] = 0.571f * (rf + (rf - 0.5f * ce));  /* FR */
         dst[2] = ce;  /* FC */
@@ -492,6 +493,7 @@ SDL_ConvertQuadTo51(SDL_AudioCVT * cvt, SDL_AudioFormat format)
         lb = src[2];
         rb = src[3];
         ce = (lf + rf) * 0.5f;
+        /* Constant 0.571f is approx 4/7 not to saturate */
         dst[0] = 0.571f * (lf + (lf - 0.5f * ce)); /* FL */
         dst[1] = 0.571f * (rf + (rf - 0.5f * ce));  /* FR */
         dst[2] = ce;  /* FC */