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Use two different buffer sizes for alsa -- a short one for software mixer, a longer one for hardware mixer, giving more resilience against delays, etc. without affecting responsiveness

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This commit is contained in:
Mike Brady
2015-06-18 16:14:40 +00:00
parent 7626cc2f2e
commit 193fd3f0ca
2 changed files with 24 additions and 5 deletions
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audio_alsa.c
+22 -4
View File
@@ -95,23 +95,39 @@ static void help(void) {
static int init(int argc, char **argv) {
const char *str;
int value;
uint32_t buffer_length_hardware = 22050;
int hardware_mixer = 0;
config.audio_backend_buffer_desired_length = 6615; // this is the default for ALSA
config.audio_backend_latency_offset = 0; // this is the default for ALSA
config.audio_backend_buffer_desired_length = 6615; // default for alsa with a software mixer
// get settings from settings file first, allow them to be over-ridden by command line options
if (config.cfg != NULL) {
/* Get the desired buffer size setting. */
if (config_lookup_int(config.cfg, "alsa.audio_backend_buffer_desired_length", &value)) {
if (config_lookup_int(config.cfg, "alsa.audio_backend_buffer_desired_length_software", &value)) {
if ((value < 0) || (value > 66150))
die("Invalid alsa audio backend buffer desired length \"%d\". It should be between 0 and "
die("Invalid alsa audio backend buffer desired length (software) \"%d\". It should be between 0 and "
"66150, default is 6615",
value);
else
else {
config.audio_backend_buffer_desired_length = value;
}
}
/* Get the desired buffer size setting. */
if (config_lookup_int(config.cfg, "alsa.audio_backend_buffer_desired_length_hardware", &value)) {
if ((value < 0) || (value > 66150))
die("Invalid alsa audio backend buffer desired length (hardware) \"%d\". It should be between 0 and "
"66150, default is 22050",
value);
else {
buffer_length_hardware = value;
}
}
/* Get the latency offset. */
@@ -183,6 +199,8 @@ static int init(int argc, char **argv) {
if (!hardware_mixer)
return 0;
config.audio_backend_latency_offset = buffer_length_hardware;
if (alsa_mix_dev == NULL)
alsa_mix_dev = alsa_out_dev;
scripts/shairport-sync.conf
+2 -1
View File
@@ -59,7 +59,8 @@ alsa =
// mixer_device = "default"; //actually, the mixer default is whatever the output_device is. Normally you wouldn't have to use this.
// mixer_control_name = "PCM"; // the name of the mixer to use -- there is no default.
// audio_backend_latency_offset = 0; // Set this offset to compensate for a fixed delay in the audio back end. E.g. if the output device delays by 100 ms, set this to -4410.
// audio_backend_buffer_desired_length = 6615; // If set too small, buffer underflow occurs on low-powered machines. Too long and the response times with software mixer become annoying.
// audio_backend_buffer_desired_length_software = 6615; // If set too small, buffer underflow occurs on low-powered machines. Too long and the response times with software mixer become annoying.
// audio_backend_buffer_desired_length_hardware = 22050; // If set too large, there is less opportunity for late packets to be retrieved.
};
// These are parameters for the pipe back end, an experimental back end that directs output to a pipe.