aaudio: Make input preset into a hint, don't set it by default.

Fixes #16130.
Reference Issue #13402.

include/SDL3/SDL_hints.h

@@ -117,6 +117,33 @@ extern "C" {
  */
 #define SDL_HINT_ANDROID_LOW_LATENCY_AUDIO "SDL_ANDROID_LOW_LATENCY_AUDIO"
 
+/**
+ * A variable to control Android's AAudio input preset.
+ *
+ * This hint only applies to SDL's "aaudio" backend on Android 9+ devices.
+ *
+ * Some devices choose the wrong microphone by default (between the one meant
+ * to be spoken in when the phone is held to the user's ear for a phone call,
+ * or an external microphone that's meant to be used when recording video),
+ * or have DSP effects applied to the recorded audio, and changing the input
+ * preset can help control this.
+ *
+ * This can be any number that maps to an `AAUDIO_INPUT_PRESET_*` enum from
+ * the Android NDK headers. The most reasonable choices are 5 ("camcorder",
+ * for external microphones) and 7 ("voice communication", for speaking
+ * directly into the device like a mobile phone). 6 ("voice recognition")
+ * might also be a useful choice.
+ *
+ * If unset (the default), SDL will not specify an input preset at all, which
+ * lets the system choose. This is usually the correct thing to do unless
+ * your app is having problems.
+ *
+ * This hint should be set before a recording audio device is opened.
+ *
+ * \since This hint is available since SDL 3.4.16.
+ */
+#define SDL_HINT_ANDROID_AAUDIO_INPUT_PRESET "SDL_ANDROID_AAUDIO_INPUT_PRESET"
+
 /**
  * A variable to control whether we trap the Android back button to handle it
  * manually.

src/audio/aaudio/SDL_aaudio.c

@@ -368,9 +368,13 @@ static bool BuildAAudioStream(SDL_AudioDevice *device)
     SetOptionalStreamUsage(builder);
 
     if (recording && ctx.AAudioStreamBuilder_setInputPreset) {    // optional API: requires Android 28
-        // try to use a microphone that is for recording external audio. Otherwise Android might choose the mic used for talking
-        // on the telephone when held to the user's ear, which is often not useful at any distance from the device.
-        ctx.AAudioStreamBuilder_setInputPreset(builder, AAUDIO_INPUT_PRESET_CAMCORDER);
+        const char *hint = SDL_GetHint(SDL_HINT_ANDROID_AAUDIO_INPUT_PRESET);
+        if (hint) {
+            const aaudio_input_preset_t preset = (const aaudio_input_preset_t) SDL_atoi(hint);
+            if (preset) {
+                ctx.AAudioStreamBuilder_setInputPreset(builder, preset);
+            }
+        }
     }
 
     LOGI("AAudio Try to open %u hz %s %u channels samples %u",