audio/out: add libmpv callback driver

This adds an ao driver that can be used to register a callback with
libmpv to get raw PCM data. Useful for embedding mpv in applications
such as game engines, which need the audio to be played in a 3D world
and spatialized.

Signed-off-by: Orion Moonclaw <webmaster@fawx.news>

Author: OrionMoonclaw

DOCS/client-api-changes.rst

@@ -32,6 +32,8 @@ API changes
 
 ::
 
+ --- mpv 0.41.0 ---
+ 2.6    - add mpv_set_audio_callback()
  --- mpv 0.40.0 ---
  2.5    - Deprecate MPV_RENDER_PARAM_AMBIENT_LIGHT. no replacement.
  --- mpv 0.39.0 ---

audio/out/ao.c

@@ -51,6 +51,7 @@ extern const struct ao_driver audio_out_opensles;
 extern const struct ao_driver audio_out_null;
 extern const struct ao_driver audio_out_alsa;
 extern const struct ao_driver audio_out_wasapi;
+extern const struct ao_driver audio_out_libmpv;
 extern const struct ao_driver audio_out_pcm;
 extern const struct ao_driver audio_out_lavc;
 extern const struct ao_driver audio_out_sdl;
@@ -104,6 +105,7 @@ static const struct ao_driver * const audio_out_drivers[] = {
 #if HAVE_COREAUDIO
     &audio_out_coreaudio_exclusive,
 #endif
+    &audio_out_libmpv,
     &audio_out_pcm,
     &audio_out_lavc,
 };

audio/out/ao_libmpv.c

@@ -0,0 +1,107 @@
+/*
+ * libmpv audio output driver
+ *
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "ao.h"
+#include "audio/format.h"
+#include "ao_libmpv.h"
+#include "internal.h"
+#include "common/msg.h"
+
+struct priv {
+    void (*write_cb)(void *userdata, const void *data, int bytes);
+    void *userdata;
+};
+
+void ao_libmpv_set_cb(struct ao *ao, void (*cb)(void *userdata, const void *data, int bytes), void *userdata)
+{
+    struct priv *p = ao->priv;
+    p->write_cb = cb;
+    p->userdata = userdata;
+}
+
+static int init(struct ao *ao)
+{
+    ao->format = af_fmt_from_planar(ao->format);
+
+    struct mp_chmap_sel sel = {0};
+    mp_chmap_sel_add_waveext(&sel);
+    if (!ao_chmap_sel_adjust(ao, &sel, &ao->channels))
+        return -1;
+
+    ao->bps = ao->channels.num * (int64_t)ao->samplerate * af_fmt_to_bytes(ao->format);
+
+    MP_INFO(ao, "libmpv: Samplerate: %d Hz Channels: %d Format: %s\n",
+        ao->samplerate, ao->channels.num, af_fmt_to_str(ao->format));
+
+    ao->untimed = true;
+    ao->device_buffer = 1 << 16;
+
+    return 0;
+}
+
+static void uninit(struct ao *ao)
+{
+}
+
+static bool audio_write(struct ao *ao, void **data, int samples)
+{
+    struct priv *priv = ao->priv;
+    const int len = samples * ao->sstride;
+
+    if (priv->write_cb)
+        priv->write_cb(priv->userdata, data[0], len);
+
+    return true;
+}
+
+static void get_state(struct ao *ao, struct mp_pcm_state *state)
+{
+    state->free_samples = ao->device_buffer;
+    state->queued_samples = 0;
+    state->delay = 0;
+}
+
+static bool set_pause(struct ao *ao, bool paused)
+{
+    return true; // signal support so common code doesn't write silence
+}
+
+static void start(struct ao *ao)
+{
+    // we use data immediately
+}
+
+static void reset(struct ao *ao)
+{
+}
+
+#define OPT_BASE_STRUCT struct priv
+
+const struct ao_driver audio_out_libmpv = {
+    .description = "libmpv audio output with a callback",
+    .name      = "libmpv",
+    .init      = init,
+    .uninit    = uninit,
+    .get_state = get_state,
+    .set_pause = set_pause,
+    .write     = audio_write,
+    .start     = start,
+    .reset     = reset,
+    .priv_size = sizeof(struct priv),
+};

audio/out/ao_libmpv.h

@@ -0,0 +1,24 @@
+/*
+ * libmpv audio output driver
+ *
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "ao.h"
+
+void ao_libmpv_set_cb(struct ao *ao, void (*cb)(void *userdata, const void *data, int bytes), void *userdata);

include/mpv/client.h

@@ -248,7 +248,7 @@ extern "C" {
  * relational operators (<, >, <=, >=).
  */
 #define MPV_MAKE_VERSION(major, minor) (((major) << 16) | (minor) | 0UL)
-#define MPV_CLIENT_API_VERSION MPV_MAKE_VERSION(2, 5)
+#define MPV_CLIENT_API_VERSION MPV_MAKE_VERSION(2, 6)
 
 /**
  * The API user is allowed to "#define MPV_ENABLE_DEPRECATED 0" before
@@ -1768,6 +1768,18 @@ MPV_EXPORT void mpv_wakeup(mpv_handle *ctx);
  */
 MPV_EXPORT void mpv_set_wakeup_callback(mpv_handle *ctx, void (*cb)(void *d), void *d);
 
+ /**
+ * Set a custom function that should be called on new audio data.
+ * Raw PCM is passed in as an argument to the callback, the format should be set before init using appropriate options.
+ *
+ * This can only be used with ao_libmpv and must be called before the ao is initialized (so before playback starts).
+ * Only one audio callback can be set per instance.
+ *
+ * @param cb function that should be called on audio data
+ * @param d arbitrary userdata passed to cb
+ */
+MPV_EXPORT int mpv_set_audio_callback(mpv_handle *ctx, void (*cb)(void *d, const void *data, int bytes), void *d);
+
 /**
  * Block until all asynchronous requests are done. This affects functions like
  * mpv_command_async(), which return immediately and return their result as

meson.build

@@ -72,6 +72,7 @@ sources = files(
     'audio/out/ao.c',
     'audio/out/ao_lavc.c',
     'audio/out/ao_null.c',
+    'audio/out/ao_libmpv.c',
     'audio/out/ao_pcm.c',
     'audio/out/buffer.c',
 

player/audio.c

@@ -21,6 +21,8 @@
 #include <limits.h>
 #include <math.h>
 #include <assert.h>
+#include <audio/out/ao_libmpv.h>
+#include <audio/out/internal.h>
 
 #include "mpv_talloc.h"
 
@@ -447,6 +449,9 @@ static int reinit_audio_filters_and_output(struct MPContext *mpctx)
                              mpctx, mpctx->encode_lavc_ctx, out_rate,
                              out_format, out_channels);
 
+    if (strcmp(mpctx->ao->driver->name, "libmpv") == 0)
+        ao_libmpv_set_cb(mpctx->ao, mpctx->ao_libmpv_cb, mpctx->ao_libmpv_userdata);
+
     int ao_rate = 0;
     int ao_format = 0;
     struct mp_chmap ao_channels = {0};

player/client.c

@@ -47,6 +47,9 @@
 #include "core.h"
 #include "client.h"
 
+#include <audio/out/internal.h>
+#include <audio/out/ao_libmpv.h>
+
 /*
  * Locking hierarchy:
  *
@@ -2245,3 +2248,14 @@ bool mp_streamcb_lookup(struct mpv_global *g, const char *protocol,
     mp_mutex_unlock(&clients->lock);
     return found;
 }
+
+int mpv_set_audio_callback(mpv_handle *ctx, void (*cb)(void *userdata, const void *data, int bytes), void *userdata)
+{
+    lock_core(ctx);
+
+    ctx->mpctx->ao_libmpv_cb = cb;
+    ctx->mpctx->ao_libmpv_userdata = userdata;
+
+    unlock_core(ctx);
+    return MPV_ERROR_SUCCESS;
+}

player/core.h

@@ -324,6 +324,10 @@ typedef struct MPContext {
     struct mp_aframe *ao_filter_fmt; // for weak gapless audio check
     struct ao_chain *ao_chain;
 
+    // Callback that will be set for ao_libmpv
+    void (*ao_libmpv_cb)(void *userdata, const void *data, int bytes);
+    void *ao_libmpv_userdata;
+
     struct vo_chain *vo_chain;
 
     struct vo *video_out;