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Suggestion for very-low-latency mode on portaudio

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- Needed to keep audio in sync when playing rhythm game machines such
as konami system 573. This is because the lowest audio_latency currently
supported (audio_latency 1) introduces at least 10 ms of variable latency.
I am unsure how to go about this without breaking backward compatibility
so I set it to work only when audio_latency is 0 (which was previously ignored
by mame itself and was treated equivalent to audio_latency 1). I am aware
that setting audio_latency to 0 is not supported by many mame frontends,
but this change seems natural. Otherwise, would it be better to add
a new mame.ini option, or to automatically enable this low-latency mode
when pa_latency is set lower than, say, 0.01 (10ms), which would
break people's configurations if they already rely on the old behavior?
This commit is contained in:
Eric Vidal 2019-07-14 19:41:20 +08:00
parent a5fdcb40f8
commit 1ccdfb873a
1 changed files with 27 additions and 8 deletions
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21
src/osd/modules/sound/pa_sound.cpp
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@ -132,7 +132,7 @@ private:
enum
{
LATENCY_MIN = 1,
LATENCY_MIN = 0,
LATENCY_MAX = 5,
};
@ -261,8 +261,16 @@ int sound_pa::init(osd_options const &options)
// clamp to a probable figure
callback_interval = std::min<double>(callback_interval, 20.0);
if (m_audio_latency == 0)
{
// very-low-latency mode (set audio_latency to 0); pa_latency controls allowable audio jitter
m_skip_threshold = (options.pa_latency() ? options.pa_latency() : device_info->defaultLowOutputLatency) * m_sample_rate * 2 + 0.5f;
}
else
{
// set the best guess callback interval to allowed count, each audio_latency step > 1 adds 20 ms
m_skip_threshold = ((std::max<double>(callback_interval, 10.0) + (m_audio_latency - 1) * 20.0) / 1000.0) * m_sample_rate * 2 + 0.5f;
}
osd_printf_verbose("PortAudio: Using device \"%s\" on API \"%s\"\n", device_info->name, api_info->name);
osd_printf_verbose("PortAudio: Sample rate is %0.0f Hz, device output latency is %0.2f ms\n",
@ -342,6 +350,16 @@ int sound_pa::callback(s16* output_buffer, size_t number_of_samples)
// if we have been above the set threshold for ~1 second, skip forward
if (m_osd_ticks - m_skip_threshold_ticks > m_osd_tps)
{
if (m_audio_latency == 0)
{
// in very-low-latency mode, always skip forward the whole way
// to prevent input from appearing delayed (due to sound cues getting delayed)
m_ab->increment_playpos(m_buffer_min_ct);
//osd_printf_verbose("PortAudio: skip ahead %d samples\n", m_buffer_min_ct);
m_has_overflowed = true;
}
else
{
int adjust = m_buffer_min_ct - m_skip_threshold / 2;
@ -350,6 +368,7 @@ int sound_pa::callback(s16* output_buffer, size_t number_of_samples)
m_ab->increment_playpos(adjust);
m_has_overflowed = true;
}
}
m_skip_threshold_ticks = m_osd_ticks;
m_buffer_min_ct = INT_MAX;