Use audio callback

The libretro frontend now controls audio, and can now therefore pause
the video and audio.
This requires a modified version of libmpv which is not currently
upstream: 789aa4528e

Not that all audio is currently converted to 48000Hz.

Squashed commit of the following:

commit ef16a4045e36cb9acd87ef2632d57f7380494781
Author: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>
Date:   Mon Feb 12 22:29:52 2018 +0000

    Working audio-cb

    Audio currently resampled to 48kHz.

    Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>

commit 0b430219b8cae47af4f0f32611f888d51c3393b1
Author: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>
Date:   Mon Feb 12 19:23:38 2018 +0000

    Minor audio-cb changes for testing

    Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>

commit 65a2ebe354066839bd8e27584684c901709a1c2b
Author: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>
Date:   Mon Feb 12 16:51:53 2018 +0000

    WIP: use mpv audio-cb output

    Audio quality and timing is poor.

    Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>

commit ce22b385461c087217542b2a4c1e0f01ea530164
Author: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>
Date:   Mon Feb 12 10:22:53 2018 +0000

    Remove spaces

    Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>

Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>

libretro.h

@@ -2222,6 +2222,7 @@ typedef void (RETRO_CALLCONV *retro_audio_sample_t)(int16_t left, int16_t right)
  * One frame is defined as a sample of left and right channels, interleaved.
  * I.e. int16_t buf[4] = { l, r, l, r }; would be 2 frames.
  * Only one of the audio callbacks must ever be used.
+ * Limited to a maximum of 1024 samples.
  */
 typedef size_t (RETRO_CALLCONV *retro_audio_sample_batch_t)(const int16_t *data,
       size_t frames);

mpv-libretro.c

@@ -1,16 +1,16 @@
 /* mpv media player libretro core
  * Copyright (C) 2018 Mahyar Koshkouei
- * 
+ *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation, either version 3 of the License, or
  * (at your option) any later version.
- * 
+ *
  * This program 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 General Public License for more details.
- * 
+ *
  * You should have received a copy of the GNU General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
@@ -56,6 +56,13 @@ static int64_t *playback_time = 0;
 /* filepath required globaly as mpv is reopened on context change */
 static char *filepath = NULL;
 
+static volatile int frame_queue = 0;
+
+void queue_new_frame(void *cb_ctx)
+{
+	frame_queue++;
+}
+
 static void fallback_log(enum retro_log_level level, const char *fmt, ...)
 {
 	(void)level;
@@ -193,7 +200,7 @@ void retro_get_system_info(struct retro_system_info *info)
 
 void retro_get_system_av_info(struct retro_system_av_info *info)
 {
-	float sampling_rate = 48000.0f;
+	float sampling_rate = 44100.0f;
 
 	struct retro_variable var = { .key = "test_aspect" };
 	environ_cb(RETRO_ENVIRONMENT_GET_VARIABLE, &var);
@@ -294,6 +301,10 @@ static void context_reset(void)
 		goto err;
 	}
 
+	mpv_opengl_cb_set_update_callback(mpv_gl, queue_new_frame, NULL);
+
+	mpv_set_option_string(mpv, "ao", "audio-cb");
+
 	if(mpv_set_option_string(mpv, "hwdec", "auto") < 0)
 		log_cb(RETRO_LOG_ERROR, "failed to set hwdec option\n");
 
@@ -317,6 +328,11 @@ static void context_reset(void)
 		usleep(10);
 	}
 
+	/* TODO #2: Check for the highest samplerate in audio stream, and use that.
+	 * Fall back to 48kHz otherwise.
+	 */
+	mpv_set_option_string(mpv, "audio-samplerate", "48000");
+
 	log_cb(RETRO_LOG_INFO, "Context reset.\n");
 
 	return;
@@ -381,20 +397,25 @@ void retro_reset(void)
 	return;
 }
 
-#if 0
 static void audio_callback(void)
 {
-	static unsigned phase;
+	/* Obtain len samples to reduce lag. */
+	int len = 2*1024;
+	static int16_t frames[512];
 
-	for (unsigned i = 0; i < 30000 / 60; i++, phase++)
+	while(len > 0)
 	{
-		int16_t val = 0x800 * sinf(2.0f * M_PI * phase * 300.0f / 30000.0f);
+		int mpv_len = mpv_audio_callback(&frames, len > 512 ? 512*2 : len*2);
-		audio_cb(val, val);
+		//printf("mpv cb: %d\n", mpv_len);
-	}
+		if(mpv_len < 1)
+			return;
 
-	phase %= 100;
+		len -= mpv_len;
+
+		//printf("acb: %lu\n", audio_batch_cb(frames, mpv_len));
+		audio_batch_cb(frames, mpv_len);
+	}
 }
-#endif
 
 static void retropad_update_input(void)
 {
@@ -414,7 +435,7 @@ static void retropad_update_input(void)
 	/* A ternary operator is used since input_state_cb returns an int16_t, but
 	 * we only care about whether the button is on or off which is why we store
 	 * the value in a single bit for each button.
-	 * 
+	 *
 	 * Unsure if saving the memory is worth the extra checks, costing CPU time,
 	 * but both are incredibly miniscule anyway.
 	 */
@@ -471,7 +492,7 @@ void retro_run(void)
 	 * retro_get_system_av_info() call.
 	 */
 	static bool updated_video_dimensions = false;
-	static int64_t width, height;
+	static int64_t width = 0, height = 0;
 
 	if(updated_video_dimensions == false)
 	{
@@ -493,18 +514,37 @@ void retro_run(void)
 			.aspect_ratio = -1,
 		};
 
-		environ_cb(RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO, &geometry);
+		struct retro_system_timing timing = {
+			.fps = 60.0f,
+			.sample_rate = 48000.0f,
+		};
+
+		struct retro_system_av_info av_info = {
+			.geometry = geometry,
+			.timing = timing,
+		};
+
+		if(width > 0 && height > 0)
+			environ_cb(RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO, &av_info);
+
 		updated_video_dimensions = true;
 	}
 
 	print_mpv_logs();
 
 	retropad_update_input();
-	/* TODO #2: Implement an audio callback feature in to libmpv */
-	/* audio_callback(); */
 
-	mpv_opengl_cb_draw(mpv_gl, hw_render.get_current_framebuffer(), width, height);
+	if(frame_queue > 0)
-	video_cb(RETRO_HW_FRAME_BUFFER_VALID, width, height, 0);
+	{
+		mpv_opengl_cb_draw(mpv_gl, hw_render.get_current_framebuffer(), width, height);
+		video_cb(RETRO_HW_FRAME_BUFFER_VALID, width, height, 0);
+		frame_queue--;
+	}
+	else
+		video_cb(NULL, width, height, 0);
+
+	/* TODO #2: Implement an audio callback feature in to libmpv */
+	audio_callback();
 	return;
 }