diff --git a/docs/audio-input.md b/docs/audio-input.md
new file mode 100644
index 00000000..ef51d705
--- /dev/null
+++ b/docs/audio-input.md
@@ -0,0 +1,30 @@
+# Polling audio input
+
+The runtime connects Ocarina's polling `nn::audio` input calls to SDL3's default recording device. Select the
+microphone or audio interface as the operating system's default input and enable the game's microphone control.
+Both a hummed note and an instrument received by that input go through the game's own note recognition.
+
+Audio capture opens when the game calls `OpenInputStream` and starts only on `StartInputStream`. The runtime does
+not write recordings to disk. SDL converts the input device's format to the requested PCM format and sample rate.
+The capture callback uses a bounded ring: unread overflow drops the oldest complete frames instead of retaining
+an unlimited recording while the game is paused. Stop, purge and close are distinct operations. Purging an unopened
+or failed stream is safe, including the null-stream path that previously crashed in `InputStreamImpl::Purge`.
+
+This implements the non-event polling overload used by Ocarina 1.1.1. Event-based streams, per-device selection,
+hot-unplug recovery and packed 24-bit PCM are not implemented. Statistics return a neutral 24-byte structure.
+Unsupported formats and a denied or missing recording device return an input error rather than reporting a
+successfully opened stream. Input currently follows the operating system's default recording device; there is no
+new runtime menu setting.
+
+## Validation
+
+`python tests/audio_input_check.py --toolchain C:/msys64/ucrt64` builds and runs headless checks using SDL's dummy
+audio driver. They require no game files and do not open a physical microphone. They cover sample ordering across
+ring wrap and overflow, frame counts, start/stop, repeated open/close, purge, unsupported formats and purge/read
+after a failed open. On Linux, omit `--toolchain` and install SDL3's development package and pkg-config.
+
+A separate local real-device check received mono signed PCM16 at 48 kHz, verified the 4800-frame ring remained
+bounded, and opened and closed the device three times. In an Ocarina 1.1.1 Windows session built from the 0.5.0
+runtime, the player enabled the ocarina microphone control and confirmed that it worked without the previous crash.
+The game's actual requested format was mono signed PCM16 at 48 kHz, capacity 4800 frames. The experimental session
+does not establish compatibility with other game updates, drivers or input devices.
diff --git a/runtime/audio_capture.c b/runtime/audio_capture.c
new file mode 100644
index 00000000..229bcafe
--- /dev/null
+++ b/runtime/audio_capture.c
@@ -0,0 +1,156 @@
+#include "audio_capture.h"
+#include <SDL3/SDL.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct MicCapture {
+    SDL_AudioStream *stream;
+    unsigned char *ring;
+    int cap, head, used, bpf;
+};
+
+const char *mic_error(void) { return SDL_GetError(); }
+int mic_device_count(void) {
+    if (!SDL_InitSubSystem(SDL_INIT_AUDIO))
+        return 0;
+    int n = 0;
+    SDL_AudioDeviceID *ids = SDL_GetAudioRecordingDevices(&n);
+    SDL_free(ids);
+    SDL_QuitSubSystem(SDL_INIT_AUDIO);
+    return n;
+}
+
+/* The SDL stream lock serializes the callback and every ring operation.
+   Discard the oldest frames on overflow, so a paused game cannot grow RAM. */
+static void SDLCALL received(void *userdata, SDL_AudioStream *stream, int added, int total) {
+    (void)added;
+    (void)total;
+    MicCapture *m = userdata;
+    unsigned char scratch[8192];
+    int chunk = (int)sizeof scratch / m->bpf * m->bpf;
+    for (;;) {
+        int n = SDL_GetAudioStreamData(stream, scratch, chunk);
+        if (n <= 0)
+            break;
+        n -= n % m->bpf;
+        if (!n)
+            break;
+        const unsigned char *src = scratch;
+        if (n > m->cap) {
+            src += n - m->cap;
+            n = m->cap;
+        }
+        int drop = m->used + n - m->cap;
+        if (drop > 0) {
+            m->head = (m->head + drop) % m->cap;
+            m->used -= drop;
+        }
+        int tail = (m->head + m->used) % m->cap;
+        int first = n < m->cap - tail ? n : m->cap - tail;
+        memcpy(m->ring + tail, src, first);
+        memcpy(m->ring, src + first, n - first);
+        m->used += n;
+    }
+}
+
+MicCapture *mic_open(int format, int channels, int rate, int frames) {
+    SDL_AudioFormat sf;
+    switch (format) {
+    case 1:
+        sf = SDL_AUDIO_S8;
+        break;
+    case 2:
+        sf = SDL_AUDIO_S16LE;
+        break;
+    case 4:
+        sf = SDL_AUDIO_S32LE;
+        break;
+    case 5:
+        sf = SDL_AUDIO_F32LE;
+        break;
+    default:
+        SDL_SetError("unsupported guest sample format %d", format);
+        return NULL;
+    }
+    if (channels < 1 || channels > 8 || rate < 8000 || rate > 192000 || frames < 1) {
+        SDL_SetError("invalid capture format or capacity");
+        return NULL;
+    }
+    if (!SDL_InitSubSystem(SDL_INIT_AUDIO))
+        return NULL;
+    MicCapture *m = calloc(1, sizeof *m);
+    if (!m) {
+        SDL_QuitSubSystem(SDL_INIT_AUDIO);
+        return NULL;
+    }
+    m->bpf = channels * (SDL_AUDIO_BITSIZE(sf) / 8);
+    if (frames > rate * 2)
+        frames = rate * 2;
+    m->cap = frames * m->bpf;
+    m->ring = malloc(m->cap);
+    if (!m->ring) {
+        free(m);
+        SDL_QuitSubSystem(SDL_INIT_AUDIO);
+        return NULL;
+    }
+    SDL_AudioSpec spec = {.format = sf, .channels = channels, .freq = rate};
+    m->stream = SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_RECORDING, &spec, received, m);
+    if (!m->stream) {
+        free(m->ring);
+        free(m);
+        SDL_QuitSubSystem(SDL_INIT_AUDIO);
+        return NULL;
+    }
+    return m;
+}
+int mic_start(MicCapture *m) { return m && SDL_ResumeAudioStreamDevice(m->stream); }
+void mic_stop(MicCapture *m) {
+    if (m)
+        SDL_PauseAudioStreamDevice(m->stream);
+}
+void mic_close(MicCapture *m) {
+    if (!m)
+        return;
+    SDL_DestroyAudioStream(m->stream); /* joins capture before freeing userdata */
+    free(m->ring);
+    free(m);
+    SDL_QuitSubSystem(SDL_INIT_AUDIO);
+}
+void mic_purge(MicCapture *m) {
+    if (!m)
+        return;
+    SDL_LockAudioStream(m->stream);
+    SDL_ClearAudioStream(m->stream);
+    m->head = m->used = 0;
+    SDL_UnlockAudioStream(m->stream);
+}
+int mic_available(MicCapture *m) {
+    if (!m)
+        return 0;
+    SDL_LockAudioStream(m->stream);
+    int frames = m->used / m->bpf;
+    SDL_UnlockAudioStream(m->stream);
+    return frames;
+}
+int mic_capacity(MicCapture *m) { return m ? m->cap / m->bpf : 0; }
+int mic_read(MicCapture *m, void *out, int frames) {
+    if (!m || !out || frames <= 0)
+        return 0;
+    SDL_LockAudioStream(m->stream);
+    int avail = m->used / m->bpf;
+    if (frames > avail)
+        frames = avail;
+    int n = frames * m->bpf;
+    int first = n < m->cap - m->head ? n : m->cap - m->head;
+    memcpy(out, m->ring + m->head, first);
+    memcpy((unsigned char *)out + first, m->ring, n - first);
+    m->head = (m->head + n) % m->cap;
+    m->used -= n;
+    SDL_UnlockAudioStream(m->stream);
+    return frames;
+}
+void mic_gain(MicCapture *m, float gain) {
+    if (m)
+        SDL_SetAudioStreamGain(m->stream, gain);
+}
diff --git a/runtime/audio_capture.h b/runtime/audio_capture.h
new file mode 100644
index 00000000..0422b085
--- /dev/null
+++ b/runtime/audio_capture.h
@@ -0,0 +1,14 @@
+#pragma once
+#include <stdint.h>
+typedef struct MicCapture MicCapture;
+int mic_device_count(void);
+MicCapture *mic_open(int format, int channels, int rate, int frames);
+int mic_start(MicCapture *m);
+void mic_stop(MicCapture *m);
+void mic_close(MicCapture *m);
+void mic_purge(MicCapture *m);
+int mic_available(MicCapture *m);
+int mic_read(MicCapture *m, void *out, int frames);
+int mic_capacity(MicCapture *m);
+void mic_gain(MicCapture *m, float gain);
+const char *mic_error(void);
diff --git a/runtime/ov_audio_input.c b/runtime/ov_audio_input.c
new file mode 100644
index 00000000..94916f2a
--- /dev/null
+++ b/runtime/ov_audio_input.c
@@ -0,0 +1,180 @@
+/* Polling audio input for the public nn::audio calls Ocarina imports.
+   SDL converts the default recording device to the format the caller requests. */
+#include "audio_capture.h"
+#include "host.h"
+#include "ipc.h"
+#include "platform/platform.h"
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+
+#define BAD_INPUT 0x70899u
+typedef struct {
+    uint64_t key;
+    MicCapture *mic;
+    int format[3], bpf, running;
+    uint64_t frames_read, next_log;
+} Input;
+static Input inputs[8];
+static const char input_name[] = "WindowsDefaultMicrophone";
+static Input *find(uint64_t key) {
+    for (int i = 0; i < 8; i++)
+        if (inputs[i].key == key && key)
+            return &inputs[i];
+    return NULL;
+}
+static void name_out(uint64_t addr) {
+    char *p = ipc_guest(addr, 256);
+    memset(p, 0, 256);
+    memcpy(p, input_name, sizeof input_name);
+}
+static void list_devices(Cpu *c) {
+    int n = mic_device_count();
+    if ((int)c->x[1] > 0 && n > 0)
+        name_out(c->x[0]);
+    rt_log("mic: input enumeration: %d Windows recording devices", n);
+    ret_x(c, (int)c->x[1] > 0 && n > 0 ? 1 : 0);
+}
+static void default_device(Cpu *c) {
+    name_out(c->x[0]);
+    ret_x(c, 0);
+}
+
+static void close_input(Cpu *c) {
+    Input *s = find(c->x[0]);
+    if (s) {
+        rt_log("mic: close, %llu real audio frames delivered", (unsigned long long)s->frames_read);
+        mic_close(s->mic);
+        memset(s, 0, sizeof *s);
+    }
+    if (c->x[0]) {
+        uint64_t zero = 0;
+        memcpy(ipc_guest(c->x[0], 8), &zero, 8);
+    }
+    ret_x(c, 0);
+}
+static void open_input(Cpu *c) {
+    uint64_t key = c->x[0];
+    int f[3];
+    memcpy(f, ipc_guest(c->x[4], 12), 12);
+    int frames = (int)c->x[5];
+    rt_log("mic: OpenInputStream format=%d channels=%d rate=%d capacity=%d", f[0], f[1], f[2], frames);
+    Input *s = find(key);
+    if (s) {
+        mic_close(s->mic);
+        memset(s, 0, sizeof *s);
+    }
+    for (int i = 0; !s && i < 8; i++)
+        if (!inputs[i].key)
+            s = &inputs[i];
+    uint64_t zero = 0;
+    memcpy(ipc_guest(key, 8), &zero, 8);
+    if (!s) {
+        ret_x(c, BAD_INPUT);
+        return;
+    }
+    MicCapture *m = mic_open(f[0], f[1], f[2], frames);
+    if (!m) {
+        rt_log("mic: cannot open Windows default input: %s", mic_error());
+        ret_x(c, BAD_INPUT);
+        return;
+    }
+    s->key = key;
+    s->mic = m;
+    memcpy(s->format, f, 12);
+    s->bpf = f[1] * (f[0] == 1 ? 1 : f[0] == 2 ? 2 : 4);
+    s->next_log = (uint64_t)f[2] * 5;
+    uint64_t impl = key + 8;
+    memcpy(ipc_guest(key, 8), &impl, 8);
+    rt_log("mic: Windows default input opened; bounded buffer %d frames", mic_capacity(m));
+    ret_x(c, 0);
+}
+static void start_input(Cpu *c) {
+    Input *s = find(c->x[0]);
+    if (!s || !mic_start(s->mic)) {
+        rt_log("mic: start failed: %s", mic_error());
+        ret_x(c, BAD_INPUT);
+        return;
+    }
+    s->running = 1;
+    rt_log("mic: capture started");
+    ret_x(c, 0);
+}
+static void stop_input(Cpu *c) {
+    Input *s = find(c->x[0]);
+    if (s) {
+        mic_stop(s->mic);
+        s->running = 0;
+    }
+    ret_x(c, 0);
+}
+static void purge_input(Cpu *c) {
+    Input *s = find(c->x[0]);
+    if (s)
+        mic_purge(s->mic);
+    ret_x(c, 0);
+}
+static void filled(Cpu *c) {
+    Input *s = find(c->x[0]);
+    ret_x(c, s ? mic_available(s->mic) : 0);
+}
+static void state(Cpu *c) {
+    Input *s = find(c->x[0]);
+    ret_x(c, s ? (s->running ? 2 : 1) : 0);
+}
+static void read_input(Cpu *c) {
+    Input *s = find(c->x[0]);
+    int frames = (int)c->x[2];
+    if (!s || frames <= 0) {
+        ret_x(c, 0);
+        return;
+    }
+    int available = mic_available(s->mic);
+    if (frames > available)
+        frames = available;
+    if (!frames) {
+        ret_x(c, 0);
+        return;
+    }
+    int n = mic_read(s->mic, ipc_guest(c->x[1], (uint64_t)frames * s->bpf), frames);
+    s->frames_read += n;
+    if (s->frames_read >= s->next_log) {
+        rt_log("mic: delivered %llu real frames (%d Hz)", (unsigned long long)s->frames_read, s->format[2]);
+        s->next_log = s->frames_read + (uint64_t)s->format[2] * 30;
+    }
+    ret_x(c, n);
+}
+static void statistics(Cpu *c) { memset(ipc_guest(c->x[8], 24), 0, 24); }
+
+static PlatMutex input_lock = PLAT_MUTEX_INIT;
+#define LOCKED_HANDLER(fn)                                                                                             \
+    static void fn##_locked(Cpu *c) {                                                                                  \
+        plat_mutex_lock(&input_lock);                                                                                  \
+        fn(c);                                                                                                         \
+        plat_mutex_unlock(&input_lock);                                                                                \
+    }
+LOCKED_HANDLER(list_devices)
+LOCKED_HANDLER(default_device)
+LOCKED_HANDLER(open_input)
+LOCKED_HANDLER(close_input)
+LOCKED_HANDLER(start_input)
+LOCKED_HANDLER(stop_input)
+LOCKED_HANDLER(purge_input)
+LOCKED_HANDLER(filled)
+LOCKED_HANDLER(state)
+LOCKED_HANDLER(read_input)
+LOCKED_HANDLER(statistics)
+
+HOST_OVERRIDE("_ZN2nn5audio23ListVirtualInputDevicesEPNS0_15AudioDeviceNameEi", list_devices_locked);
+HOST_OVERRIDE("_ZN2nn5audio28GetDefaultVirtualInputDeviceEPNS0_15AudioDeviceNameE", default_device_locked);
+HOST_OVERRIDE("_ZN2nn5audio26GetTrueRawAudioInputDeviceEPNS0_15AudioDeviceNameE", default_device_locked);
+HOST_OVERRIDE("_ZN2nn5audio15OpenInputStreamEPNS0_15InputStreamTypeEPvmRKNS0_15AudioDeviceNameERKNS0_12StreamFormatEi",
+              open_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio16CloseInputStreamEPNS0_15InputStreamTypeE", close_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio16StartInputStreamEPNS0_15InputStreamTypeE", start_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio15StopInputStreamEPNS0_15InputStreamTypeE", stop_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio16PurgeInputStreamEPNS0_15InputStreamTypeE", purge_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio30GetInputStreamFilledFrameCountEPKNS0_15InputStreamTypeE", filled_locked);
+HOST_OVERRIDE("_ZN2nn5audio19GetInputStreamStateEPKNS0_15InputStreamTypeE", state_locked);
+HOST_OVERRIDE("_ZN2nn5audio15ReadInputStreamEPNS0_15InputStreamTypeEPvi", read_input_locked);
+HOST_OVERRIDE("_ZN2nn5audio24GetInputStreamStatisticsEPNS0_15InputStreamTypeEb", statistics_locked);
diff --git a/tests/audio_input_check.c b/tests/audio_input_check.c
new file mode 100644
index 00000000..900f8ce9
--- /dev/null
+++ b/tests/audio_input_check.c
@@ -0,0 +1,132 @@
+/* No game data or physical microphone: exercise conversion, bounded capture and the polling ABI. */
+#include "../runtime/audio_capture.c"
+#include "../runtime/ov_audio_input.c"
+#include <assert.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+static SDL_Mutex *registry_lock;
+void plat_mutex_lock(PlatMutex *m) {
+    (void)m;
+    SDL_LockMutex(registry_lock);
+}
+void plat_mutex_unlock(PlatMutex *m) {
+    (void)m;
+    SDL_UnlockMutex(registry_lock);
+}
+void *ipc_guest(uint64_t addr, uint64_t size) {
+    assert(addr && size);
+    return (void *)(uintptr_t)addr;
+}
+void rt_log(const char *fmt, ...) { (void)fmt; }
+
+static void ring_check(void) {
+    assert(SDL_InitSubSystem(SDL_INIT_AUDIO));
+    MicCapture *m = calloc(1, sizeof *m);
+    m->bpf = 2;
+    m->cap = 16;
+    m->ring = malloc(m->cap);
+    SDL_AudioSpec spec = {.format = SDL_AUDIO_S16LE, .channels = 1, .freq = 48000};
+    m->stream = SDL_CreateAudioStream(&spec, &spec);
+    assert(m->stream);
+    assert(SDL_SetAudioStreamPutCallback(m->stream, received, m));
+    int16_t first[] = {1, 2, 3, 4, 5, 6, 7, 8}, second[] = {9, 10, 11, 12, 13, 14, 15, 16}, out[16] = {0};
+    assert(SDL_PutAudioStreamData(m->stream, first, sizeof first));
+    assert(mic_available(m) == 8);
+    assert(mic_read(m, out, 3) == 3);
+    assert(out[0] == 1 && out[2] == 3);
+    assert(SDL_PutAudioStreamData(m->stream, second, sizeof second));
+    assert(mic_available(m) == 8); /* oldest unread samples were dropped */
+    assert(mic_read(m, out, 16) == 8);
+    assert(memcmp(out, second, sizeof second) == 0);
+    assert(mic_read(m, out, -1) == 0);
+    assert(SDL_PutAudioStreamData(m->stream, first, sizeof first));
+    mic_purge(m);
+    assert(mic_available(m) == 0);
+    mic_close(m);
+}
+
+static void polling_check(void) {
+    uint64_t opaque[128] = {0};
+    int format[3] = {2, 1, 48000};
+    int16_t samples[4800];
+    Cpu c = {0};
+    uint64_t key = (uintptr_t)opaque;
+    for (int repeat = 0; repeat < 3; repeat++) {
+        c.x[0] = key;
+        c.x[4] = (uintptr_t)format;
+        c.x[5] = 4800;
+        open_input_locked(&c);
+        assert(c.x[0] == 0);
+        c.x[0] = key;
+        state_locked(&c);
+        assert(c.x[0] == 1);
+        c.x[0] = key;
+        start_input_locked(&c);
+        assert(c.x[0] == 0);
+        c.x[0] = key;
+        state_locked(&c);
+        assert(c.x[0] == 2);
+        SDL_Delay(350); /* overflow the 100 ms ring, not system memory */
+        c.x[0] = key;
+        filled_locked(&c);
+        assert(c.x[0] > 0 && c.x[0] <= 4800);
+        c.x[0] = key;
+        c.x[1] = (uintptr_t)samples;
+        c.x[2] = 4800;
+        read_input_locked(&c);
+        assert(c.x[0] > 0 && c.x[0] <= 4800);
+        c.x[0] = key;
+        stop_input_locked(&c);
+        c.x[0] = key;
+        purge_input_locked(&c);
+        c.x[0] = key;
+        filled_locked(&c);
+        assert(c.x[0] == 0);
+        c.x[0] = key;
+        close_input_locked(&c);
+        assert(opaque[0] == 0);
+        c.x[0] = key;
+        purge_input_locked(&c); /* regression: Purge after failed/closed Open */
+    }
+    format[0] = 99;
+    c.x[0] = key;
+    c.x[4] = (uintptr_t)format;
+    c.x[5] = 4800;
+    open_input_locked(&c);
+    assert(c.x[0] == BAD_INPUT);
+    c.x[0] = key;
+    purge_input_locked(&c);
+    c.x[0] = key;
+    state_locked(&c);
+    assert(c.x[0] == 0);
+    c.x[0] = key;
+    c.x[1] = (uintptr_t)samples;
+    c.x[2] = 4800;
+    read_input_locked(&c);
+    assert(c.x[0] == 0);
+    unsigned char stats[32];
+    memset(stats, 0xa5, sizeof stats);
+    c.x[8] = (uintptr_t)stats;
+    statistics_locked(&c);
+    for (int i = 0; i < 24; i++)
+        assert(stats[i] == 0);
+    for (int i = 24; i < 32; i++)
+        assert(stats[i] == 0xa5);
+    mic_stop(NULL);
+    mic_purge(NULL);
+    mic_close(NULL);
+    assert(mic_available(NULL) == 0);
+}
+
+int main(void) {
+    assert(SDL_SetHint(SDL_HINT_AUDIO_DRIVER, "dummy"));
+    registry_lock = SDL_CreateMutex();
+    assert(registry_lock);
+    ring_check();
+    polling_check();
+    SDL_DestroyMutex(registry_lock);
+    puts("PASS: sample order, bounded overflow, polling frame units, reopen, purge and failed-open regression");
+    return 0;
+}
diff --git a/tests/audio_input_check.py b/tests/audio_input_check.py
new file mode 100644
index 00000000..648d0677
--- /dev/null
+++ b/tests/audio_input_check.py
@@ -0,0 +1,31 @@
+"""Build and run the input-audio regression checks without game files or recording hardware.
+
+Windows: python tests/audio_input_check.py --toolchain C:/msys64/ucrt64
+Linux: python tests/audio_input_check.py (clang and SDL3 development files via pkg-config)
+"""
+import argparse
+import os
+from pathlib import Path
+import shlex
+import shutil
+import subprocess
+
+root = Path(__file__).resolve().parents[1]
+ap = argparse.ArgumentParser(description=__doc__)
+ap.add_argument('--toolchain', type=Path)
+a = ap.parse_args()
+out = root / 'build' / 'audio-input-check'
+out.mkdir(parents=True, exist_ok=True)
+env = dict(os.environ)
+if a.toolchain:
+    env['PATH'] = str(a.toolchain / 'bin') + os.pathsep + env.get('PATH', '')
+    cc = str(a.toolchain / 'bin' / 'clang.exe')
+    flags = ['-L', str(a.toolchain / 'lib'), '-lSDL3']
+else:
+    cc = shutil.which('clang') or 'cc'
+    flags = shlex.split(subprocess.check_output(['pkg-config', '--cflags', '--libs', 'sdl3'], text=True))
+exe = out / ('audio-input-check.exe' if os.name == 'nt' else 'audio-input-check')
+subprocess.run([cc, '-std=gnu11', '-O2', '-fno-strict-aliasing', '-Wall', '-Wextra', '-Werror',
+                '-I', str(root / 'runtime'), str(root / 'tests' / 'audio_input_check.c'),
+                '-o', str(exe), *flags], env=env, check=True)
+subprocess.run([str(exe)], env=env, timeout=15, check=True)