nils/shairport-sync
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

refine the selection of precision timing to be allowed only if the device is a real hardware device

Browse Source
This commit is contained in:
Mike Brady
2019-06-17 19:43:23 +01:00
parent 9199bf24dd
commit 7013b0cc3d
1 changed files with 16 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files
audio_alsa.c
+16 -9
View File
@@ -175,10 +175,14 @@ int (*delay_and_status)(snd_pcm_state_t *state, snd_pcm_sframes_t *delay, enum y
int precision_delay_available() {
if (precision_delay_available_status == YNDK_DONT_KNOW) {
// At present, the only criterion as to whether precision delay is available
// this is very crude -- if the device is a hardware device, then it's assumed the delay is precise
const char *output_device_name = snd_pcm_name(alsa_handle);
int is_a_real_hardware_device = (strstr(output_device_name,"hw:") == output_device_name);
// The criteria as to whether precision delay is available
// is whether the device driver returns non-zero update timestamps
// If it does, it is considered precision delay is available
// Otherwise, it's considered to be unavailable
// If it does, and the device is a hardware device (i.e. its name begins with "hw:0"),
// it is considered that precision delay is available. Otherwise, it's considered to be unavailable.
// To test, we play a silence buffer (fairly large to avoid underflow)
// and then we check the delay return. It will tell us if it
@@ -213,12 +217,16 @@ int precision_delay_available() {
int ret = precision_delay_and_status(&state, &delay, &uses_update_timestamps);
// debug(3,"alsa: precision_delay_available asking for delay and status with a return status of %d, a delay of %ld and a uses_update_timestamps of %d.", ret, delay, uses_update_timestamps);
if (ret == 0) {
if (uses_update_timestamps == YNDK_YES) {
if ((uses_update_timestamps == YNDK_YES) && (is_a_real_hardware_device)) {
precision_delay_available_status = YNDK_YES;
debug(2,"alsa: precision delay timing is available.");
} else {
precision_delay_available_status = YNDK_NO;
debug(2,"alsa: precision delay timing is not available.");
if ((uses_update_timestamps == YNDK_YES) && (!is_a_real_hardware_device)) {
debug(2,"alsa: precision delay timing is not available because it's not definitely a hardware device.");
} else {
debug(2,"alsa: precision delay timing is not available.");
}
precision_delay_available_status = YNDK_NO;
}
}
}
@@ -1435,14 +1443,13 @@ int precision_delay_and_status(snd_pcm_state_t *state, snd_pcm_sframes_t *delay,
// user information
if (update_timestamp_ns == 0) {
if (delay_type_notified != 1) {
inform("Note: the alsa output device \"%s\" is not capable of high precision delay timing.", snd_pcm_name(alsa_handle));
debug(1,"alsa: delay_and_status must use snd_pcm_delay() to calculate delay");
debug(2,"alsa: update timestamps unavailable");
delay_type_notified = 1;
}
} else {
// diagnostic
if (delay_type_notified != 0) {
debug(2,"alsa: delay_and_status using snd_pcm_status_get_delay() to calculate delay");
debug(2,"alsa: update timestamps available");
delay_type_notified = 0;
}
}