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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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4
INSTALL
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@ -136,8 +136,8 @@ Libraries:
from <http://zlib.net/>
- libunistring 0.9.3+
from <http://www.gnu.org/software/libunistring/#downloading>
- libasound (optional - ALSA support, recommended for Linux)
normally already installed as part of your distro
- libasound (optional - local audio)
often already installed as part of your distro
- libplist 0.16+ (optional - iTunes XML support)
from <http://github.com/JonathanBeck/libplist/downloads>
- libspotify (optional - Spotify support)

8
forked-daapd.conf
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@ -153,7 +153,7 @@ audio {
# Name - used in the speaker list in Remote
nickname = "Computer"
# Type of the output (alsa, oss4, dummy)
# Type of the output (alsa or dummy)
# type = "alsa"
# Audio device name for local audio output
@ -162,6 +162,12 @@ audio {
# Mixer channel to use for volume control - ALSA/Linux only
# If not set, PCM will be used if available, otherwise Master.
# mixer = ""
# If your local audio is out of sync with AirPlay, you can adjust this
# value. Positive values correspond to moving local audio ahead,
# negative correspond to delaying it. The unit is samples, where is
# 44100 = 1 second. The offset must be between -44100 and 44100.
# offset = 0
}
# AirPlay/Airport Express device settings

5
src/conffile.c
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@ -94,12 +94,9 @@ static cfg_opt_t sec_audio[] =
{
CFG_STR("nickname", "Computer", CFGF_NONE),
CFG_STR("type", NULL, CFGF_NONE),
#ifdef __linux__
CFG_STR("card", "default", CFGF_NONE),
#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
CFG_STR("card", "/dev/dsp", CFGF_NONE),
#endif
CFG_STR("mixer", NULL, CFGF_NONE),
CFG_INT("offset", 0, CFGF_NONE),
CFG_END()
};

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)