From f868408a3ab7e2fbed4be9ae97a2c00d437870dc Mon Sep 17 00:00:00 2001
From: Brick <[EMAIL REDACTED]>
Date: Sat, 1 Mar 2025 12:47:10 +0000
Subject: [PATCH] Ceil the audio resampling rate to avoid over-estimating
output samples.
Reverts 580a4963917cf5057e3b4cb3d9a04b985f27dc9d, fixes #12115
---
src/audio/SDL_audioresample.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/src/audio/SDL_audioresample.c b/src/audio/SDL_audioresample.c
index 400396aba1320..371002e317ac9 100644
--- a/src/audio/SDL_audioresample.c
+++ b/src/audio/SDL_audioresample.c
@@ -587,7 +587,18 @@ Sint64 SDL_GetResampleRate(int src_rate, int dst_rate)
SDL_assert(src_rate > 0);
SDL_assert(dst_rate > 0);
- Sint64 sample_rate = ((Sint64)src_rate << 32) / (Sint64)dst_rate;
+ Sint64 numerator = (Sint64)src_rate << 32;
+ Sint64 denominator = (Sint64)dst_rate;
+
+ // Generally it's expected that `dst_frames = (src_frames * dst_rate) / src_rate`
+ // To match this as closely as possible without infinite precision, always round up the resample rate.
+ // For example, without rounding up, a sample ratio of 2:3 would have `sample_rate = 0xAAAAAAAA`
+ // After 3 frames, the position would be 0x1.FFFFFFFE, meaning we haven't fully consumed the second input frame.
+ // By rounding up to 0xAAAAAAAB, we would instead reach 0x2.00000001, fulling consuming the second frame.
+ // Technically you could say this is kicking the can 0x100000000 steps down the road, but I'm fine with that :)
+ // sample_rate = div_ceil(numerator, denominator)
+ Sint64 sample_rate = ((numerator - 1) / denominator) + 1;
+
SDL_assert(sample_rate > 0);
return sample_rate;
@@ -657,7 +668,7 @@ Sint64 SDL_GetResamplerOutputFrames(Sint64 input_frames, Sint64 resample_rate, S
}
// output_frames = div_ceil(input_offset, resample_rate)
- Sint64 output_frames = (input_offset > 0) ? ((input_offset + resample_rate * 3 / 4) / resample_rate) : 0;
+ Sint64 output_frames = (input_offset > 0) ? ((input_offset - 1) / resample_rate) + 1 : 0;
*inout_resample_offset = (output_frames * resample_rate) - input_offset;