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Ceil the audio resampling rate to avoid over-estimating output samples. 

Reverts 580a496391, fixes #12115
This commit is contained in:
Brick 2025-03-01 12:47:10 +00:00 committed by Sam Lantinga
parent cbdc93b17f
commit f868408a3a
1 changed files with 13 additions and 2 deletions
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15
src/audio/SDL_audioresample.c
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@ -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;