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[alsa] Let the user configure an offset to sync audio if required

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This commit is contained in:
ejurgensen
2016-04-13 20:12:37 +02:00
parent e23fed4ac4
commit ad01d65047
4 changed files with 23 additions and 10 deletions
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16
src/outputs/alsa.c
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@@ -54,6 +54,7 @@ static snd_mixer_t *mixer_hdl;
static snd_mixer_elem_t *vol_elem;
static long vol_min;
static long vol_max;
static int offset;
#define ALSA_F_STARTED (1 << 15)
@@ -552,13 +553,16 @@ playback_start(struct alsa_session *as, uint64_t pos, uint64_t start_pos)
// Clear prebuffer in case start somehow got called twice without a stop in between
prebuf_free(as);
// Adjust the starting position with the configured value
start_pos -= offset;
// The difference between pos and start_pos should match the 2 second
// buffer that AirPlay uses. We will not use alsa's buffer for the initial
// buffering, because my sound card's start_threshold is not to be counted on.
// Instead we allocate our own buffer, and when it is time to play we write as
// much as we can to alsa's buffer.
as->prebuf_len = (start_pos - pos) / AIRTUNES_V2_PACKET_SAMPLES + 1;
if (as->prebuf_len > 2*126)
if (as->prebuf_len > (3 * 44100 - offset) / AIRTUNES_V2_PACKET_SAMPLES)
{
DPRINTF(E_LOG, L_LAUDIO, "Sanity check of prebuf_len (%" PRIu32 " packets) failed\n", as->prebuf_len);
return;
@@ -669,7 +673,7 @@ sync_check(struct alsa_session *as, uint64_t rtptime, snd_pcm_sframes_t delay, i
npackets = 0;
pb_pos = rtptime - delay - AIRTUNES_V2_PACKET_SAMPLES * npackets;
latency = cur_pos - pb_pos;
latency = cur_pos - (pb_pos - offset);
// If the latency is low or very different from our last measurement, we reset the sync_counter
if (abs(latency) < ALSA_MAX_LATENCY || abs(as->last_latency - latency) > ALSA_MAX_LATENCY_VARIANCE)
@@ -692,7 +696,7 @@ sync_check(struct alsa_session *as, uint64_t rtptime, snd_pcm_sframes_t delay, i
as->last_latency = latency;
if (latency)
DPRINTF(E_DBG, L_LAUDIO, "Sync %d cur_pos %" PRIu64 ", pb_pos %" PRIu64 " (diff %d, delay %li), pos %" PRIu64 "\n", sync, cur_pos, pb_pos, latency, delay, as->pos);
DPRINTF(E_SPAM, L_LAUDIO, "Sync %d cur_pos %" PRIu64 ", pb_pos %" PRIu64 " (diff %d, delay %li), pos %" PRIu64 "\n", sync, cur_pos, pb_pos, latency, delay, as->pos);
return sync;
}
@@ -987,6 +991,12 @@ alsa_init(void)
card_name = cfg_getstr(cfg_audio, "card");
mixer_name = cfg_getstr(cfg_audio, "mixer");
nickname = cfg_getstr(cfg_audio, "nickname");
offset = cfg_getint(cfg_audio, "offset");
if (abs(offset) > 44100)
{
DPRINTF(E_LOG, L_LAUDIO, "The ALSA offset (%d) set in the configuration is out of bounds\n", offset);
offset = 44100 * (offset/abs(offset));
}
device = calloc(1, sizeof(struct output_device));
if (!device)