mpv/audio/out/ao_sdl.c

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/*
* audio output driver for SDL 1.2+
* Copyright (C) 2012 Rudolf Polzer <divVerent@xonotic.org>
*
* This file is part of mpv.
*
* mpv 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 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with mpv. If not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "audio/format.h"
#include "talloc.h"
#include "ao.h"
#include "internal.h"
#include "common/common.h"
#include "common/msg.h"
#include "options/m_option.h"
#include "osdep/timer.h"
#include <SDL.h>
struct priv
{
bool paused;
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float buflen;
};
static const int fmtmap[][2] = {
{AF_FORMAT_U8, AUDIO_U8},
{AF_FORMAT_S8, AUDIO_S8},
{AF_FORMAT_U16, AUDIO_U16SYS},
{AF_FORMAT_S16, AUDIO_S16SYS},
#ifdef AUDIO_S32SYS
{AF_FORMAT_S32, AUDIO_S32SYS},
#endif
#ifdef AUDIO_F32SYS
{AF_FORMAT_FLOAT, AUDIO_F32SYS},
#endif
{0}
};
static void audio_callback(void *userdata, Uint8 *stream, int len)
{
struct ao *ao = userdata;
void *data[1] = {stream};
if (len % ao->sstride)
MP_ERR(ao, "SDL audio callback not sample aligned");
// Time this buffer will take, plus assume 1 period (1 callback invocation)
// fixed latency.
double delay = 2 * len / (double)ao->bps;
ao_read_data(ao, data, len / ao->sstride, mp_time_us() + 1000000LL * delay);
}
static void uninit(struct ao *ao)
{
struct priv *priv = ao->priv;
if (!priv)
return;
if (SDL_WasInit(SDL_INIT_AUDIO)) {
// make sure the callback exits
SDL_LockAudio();
// close audio device
SDL_QuitSubSystem(SDL_INIT_AUDIO);
}
}
static unsigned int ceil_power_of_two(unsigned int x)
{
int y = 1;
while (y < x)
y *= 2;
return y;
}
static int init(struct ao *ao)
{
if (SDL_WasInit(SDL_INIT_AUDIO)) {
MP_ERR(ao, "already initialized\n");
return -1;
}
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struct priv *priv = ao->priv;
if (SDL_InitSubSystem(SDL_INIT_AUDIO)) {
if (!ao->probing)
MP_ERR(ao, "SDL_Init failed\n");
uninit(ao);
return -1;
}
struct mp_chmap_sel sel = {0};
mp_chmap_sel_add_waveext_def(&sel);
if (!ao_chmap_sel_adjust(ao, &sel, &ao->channels)) {
uninit(ao);
return -1;
}
ao->format = af_fmt_from_planar(ao->format);
SDL_AudioSpec desired, obtained;
desired.format = AUDIO_S16SYS;
for (int n = 0; fmtmap[n][0]; n++) {
if (ao->format == fmtmap[n][0]) {
desired.format = fmtmap[n][1];
break;
}
}
desired.freq = ao->samplerate;
desired.channels = ao->channels.num;
desired.samples = MPMIN(32768, ceil_power_of_two(ao->samplerate *
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priv->buflen));
desired.callback = audio_callback;
desired.userdata = ao;
MP_VERBOSE(ao, "requested format: %d Hz, %d channels, %x, "
"buffer size: %d samples\n",
(int) desired.freq, (int) desired.channels,
(int) desired.format, (int) desired.samples);
obtained = desired;
if (SDL_OpenAudio(&desired, &obtained)) {
if (!ao->probing)
MP_ERR(ao, "could not open audio: %s\n", SDL_GetError());
uninit(ao);
return -1;
}
MP_VERBOSE(ao, "obtained format: %d Hz, %d channels, %x, "
"buffer size: %d samples\n",
(int) obtained.freq, (int) obtained.channels,
(int) obtained.format, (int) obtained.samples);
// The sample count is usually the number of samples the callback requests,
// which we assume is the period size. Normally, ao.c will allocate a large
// enough buffer. But in case the period size should be pathologically
// large, this will help.
ao->device_buffer = 3 * obtained.samples;
ao->format = 0;
for (int n = 0; fmtmap[n][0]; n++) {
if (obtained.format == fmtmap[n][1]) {
ao->format = fmtmap[n][0];
break;
}
}
if (!ao->format) {
if (!ao->probing)
MP_ERR(ao, "could not find matching format\n");
uninit(ao);
return -1;
}
if (!ao_chmap_sel_get_def(ao, &sel, &ao->channels, obtained.channels)) {
uninit(ao);
return -1;
}
ao->samplerate = obtained.freq;
priv->paused = 1;
return 1;
}
audio/out/pull: remove race conditions There were subtle and minor race conditions in the pull.c code, and AOs using it (jack, portaudio, sdl, wasapi). Attempt to remove these. There was at least a race condition in the ao_reset() implementation: mp_ring_reset() was called concurrently to the audio callback. While the ringbuffer uses atomics to allow concurrent access, the reset function wasn't concurrency-safe (and can't easily be made to). Fix this by stopping the audio callback before doing a reset. After that, we can do anything without needing synchronization. The callback is resumed when resuming playback at a later point. Don't call driver->pause, and make driver->resume and driver->reset start/stop the audio callback. In the initial state, the audio callback must be disabled. JackAudio of course is different. Maybe there is no way to suspend the audio callback without "disconnecting" it (what jack_deactivate() would do), so I'm not trying my luck, and implemented a really bad hack doing active waiting until we get the audio callback into a state where it won't interfere. Once the callback goes from AO_STATE_WAIT to NONE, we can be sure that the callback doesn't access the ringbuffer or anything else anymore. Since both sched_yield() and pthread_yield() apparently are not always available, use mp_sleep_us(1) to avoid burning CPU during active waiting. The ao_jack.c change also removes a race condition: apparently we didn't initialize _all_ ao fields before starting the audio callback. In ao_wasapi.c, I'm not sure whether reset really waits for the audio callback to return. Kovensky says it's not guaranteed, so disable the reset callback - for now the behavior of ao_wasapi.c is like with ao_jack.c, and active waiting is used to deal with the audio callback.
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static void reset(struct ao *ao)
{
struct priv *priv = ao->priv;
if (!priv->paused)
SDL_PauseAudio(SDL_TRUE);
priv->paused = 1;
}
static void resume(struct ao *ao)
{
struct priv *priv = ao->priv;
if (priv->paused)
SDL_PauseAudio(SDL_FALSE);
priv->paused = 0;
}
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#define OPT_BASE_STRUCT struct priv
const struct ao_driver audio_out_sdl = {
.description = "SDL Audio",
.name = "sdl",
.init = init,
.uninit = uninit,
audio/out/pull: remove race conditions There were subtle and minor race conditions in the pull.c code, and AOs using it (jack, portaudio, sdl, wasapi). Attempt to remove these. There was at least a race condition in the ao_reset() implementation: mp_ring_reset() was called concurrently to the audio callback. While the ringbuffer uses atomics to allow concurrent access, the reset function wasn't concurrency-safe (and can't easily be made to). Fix this by stopping the audio callback before doing a reset. After that, we can do anything without needing synchronization. The callback is resumed when resuming playback at a later point. Don't call driver->pause, and make driver->resume and driver->reset start/stop the audio callback. In the initial state, the audio callback must be disabled. JackAudio of course is different. Maybe there is no way to suspend the audio callback without "disconnecting" it (what jack_deactivate() would do), so I'm not trying my luck, and implemented a really bad hack doing active waiting until we get the audio callback into a state where it won't interfere. Once the callback goes from AO_STATE_WAIT to NONE, we can be sure that the callback doesn't access the ringbuffer or anything else anymore. Since both sched_yield() and pthread_yield() apparently are not always available, use mp_sleep_us(1) to avoid burning CPU during active waiting. The ao_jack.c change also removes a race condition: apparently we didn't initialize _all_ ao fields before starting the audio callback. In ao_wasapi.c, I'm not sure whether reset really waits for the audio callback to return. Kovensky says it's not guaranteed, so disable the reset callback - for now the behavior of ao_wasapi.c is like with ao_jack.c, and active waiting is used to deal with the audio callback.
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.reset = reset,
.resume = resume,
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.priv_size = sizeof(struct priv),
.priv_defaults = &(const struct priv) {
.buflen = 0, // use SDL default
},
.options = (const struct m_option[]) {
OPT_FLOAT("buflen", buflen, 0),
{0}
},
};