sdl2-compat: audiocvt: Use src_format stored in documented SDL_AudioCVT fields

SDL Commits
1 
From 31973dca6b1856c19cf4651546bfa843579a129d Mon Sep 17 00:00:00 2001
From: Cameron Gutman <[EMAIL REDACTED]>
Date: Sun, 23 Feb 2025 15:23:57 -0600
Subject: [PATCH] audiocvt: Use src_format stored in documented SDL_AudioCVT
 fields

Real SDL2 uses this value (but not dst_format) in SDL_ConvertAudio().
---
 src/sdl2_compat.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/src/sdl2_compat.c b/src/sdl2_compat.c
index c31ac9e..71278bd 100644
--- a/src/sdl2_compat.c
+++ b/src/sdl2_compat.c
@@ -10397,7 +10397,7 @@ static bool SDL_IsSupportedChannelCount(const int channels)
 
 
 typedef struct {
-    SDL2_AudioFormat src_format;
+    /* src_format is read directly from the AudioCVT in real SDL2 */
     Uint8 src_channels;
     int src_rate;
     SDL2_AudioFormat dst_format;
@@ -10477,7 +10477,6 @@ SDL_BuildAudioCVT(SDL_AudioCVT *cvt,
 
     { /* Use the filters[] to store some data ... */
         AudioParam ap;
-        ap.src_format = src_format;
         ap.src_channels = src_channels;
         ap.src_rate = src_rate;
         ap.dst_format = dst_format;
@@ -10531,7 +10530,7 @@ SDL_DECLSPEC int SDLCALL
 SDL_ConvertAudio(SDL_AudioCVT *cvt)
 {
     SDL2_AudioStream *stream2;
-    SDL2_AudioFormat src_format, dst_format;
+    SDL2_AudioFormat dst_format;
     int src_channels, src_rate;
     int dst_channels, dst_rate;
 
@@ -10552,7 +10551,6 @@ SDL_ConvertAudio(SDL_AudioCVT *cvt)
             (Uint8 *)&cvt->filters[SDL_AUDIOCVT_MAX_FILTERS + 1] - (sizeof(AudioParam) & ~3),
             sizeof(ap));
 
-        src_format = ap.src_format;
         src_channels = ap.src_channels;
         src_rate = ap.src_rate;
         dst_format = ap.dst_format;
@@ -10561,13 +10559,13 @@ SDL_ConvertAudio(SDL_AudioCVT *cvt)
     }
 
     /* don't use the SDL3 stream directly or even SDL_ConvertAudioSamples; we want the U16 support in the sdl2-compat layer */
-    stream2 = SDL_NewAudioStream(src_format, src_channels, src_rate,
+    stream2 = SDL_NewAudioStream(cvt->src_format, src_channels, src_rate,
                                  dst_format, dst_channels, dst_rate);
     if (stream2 == NULL) {
         goto failure;
     }
 
-    src_samplesize = (SDL_AUDIO_BITSIZE(src_format) / 8) * src_channels;
+    src_samplesize = (SDL_AUDIO_BITSIZE(cvt->src_format) / 8) * src_channels;
 
     src_len = cvt->len & ~(src_samplesize - 1);
     dst_len = cvt->len * cvt->len_mult;