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ao_wasapi: Slightly improve timer accuracy

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Use QueryPerformanceCounter to improve the accuracy of
IAudioClock::GetPosition.

While this is mainly for "realtime correctness" (usually the delay is a
single sample or less), there are cases where IAudioClock::GetPosition
takes a long time to return from its call (though the documentation doesn't
define what a "long time" is), so correcting its value might be important in
case the documented possible delay happens.
This commit is contained in:
Diogo Franco (Kovensky) 2014-03-06 16:28:11 -03:00
parent 1d096f9f1b
commit fe03981bbc
1 changed files with 12 additions and 3 deletions
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15
audio/out/ao_wasapi.c
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@ -121,6 +121,7 @@ typedef struct wasapi_state {
IAudioClock *pAudioClock;
UINT64 clock_frequency; /* scale for the "samples" returned by the clock */
UINT64 sample_count; /* the amount of samples per channel written to a GetBuffer buffer */
LARGE_INTEGER qpc_frequency; /* frequency of windows' high resolution timer */
int opt_exclusive;
int opt_list;
@ -528,6 +529,8 @@ static int init_clock(struct wasapi_state *state) {
hr = IAudioClock_GetFrequency(state->pAudioClock, &state->clock_frequency);
EXIT_ON_ERROR(hr);
QueryPerformanceFrequency(&state->qpc_frequency);
state->sample_count = 0;
MP_VERBOSE(state, "IAudioClock::GetFrequency gave a frequency of %"PRIu64".\n", (uint64_t) state->clock_frequency);
@ -1362,19 +1365,25 @@ static int play(struct ao *ao, void **data, int samples, int flags)
}
static float get_device_delay(struct wasapi_state *state) {
/* where we pray that this hasn't desynced */
/* where we pray that sample_count hasn't desynced */
mp_memory_barrier();
UINT64 sample_count = state->sample_count;
UINT64 position;
UINT64 position, qpc_position;
HRESULT hr;
switch (hr = IAudioClock_GetPosition(state->pAudioClock, &position, NULL)) {
switch (hr = IAudioClock_GetPosition(state->pAudioClock, &position, &qpc_position)) {
case S_OK: case S_FALSE:
break;
default:
MP_ERR(state, "IAudioClock::GetPosition returned %s\n", explain_err(hr));
}
LARGE_INTEGER qpc_count;
QueryPerformanceCounter(&qpc_count);
UINT64 qpc_diff = (qpc_count.QuadPart * 10000000 / state->qpc_frequency.QuadPart) - qpc_position;
position += state->clock_frequency * qpc_diff / 10000000;
/* convert position to the same base as sample_count */
position = position * state->format.Format.nSamplesPerSec / state->clock_frequency;