PaStreamCallbackTimeInfo members are all 0 - c

Question

From the PortAudio docs:
Stream Timing Information
When using the callback I/O method your stream callback function
receives timing information via a pointer to a
PaStreamCallbackTimeInfo structure. This structure contains the
current time along with the estimated hardware capture and playback
time of the first sample of the input and output buffers. All times
are measured in seconds relative to a Stream-specific clock. The
current Stream clock time can be retrieved using Pa_GetStreamTime().
So PaStreamCallbackTimeInfo::currentTime somehow indicates the current time and PaStreamCallbackTimeInfo::outputBufferDacTime should indicate the output time of the first sample in the current buffer. I don't know why but, on Linux, these values are all zero for me. Maybe I'm doing something wrong. Here's the code and the output:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include "portaudio.h"
#define PI 3.14159265359
#define SRATE 44100
#define FREQ 440
#define DURATION 5000
int
audio_callback(
const void* inbuf,
void* outbuf,
unsigned long bufsize,
const PaStreamCallbackTimeInfo* time_info,
PaStreamCallbackFlags status_flags,
void* user_data)
{
(void)inbuf;
(void)status_flags;
double* phase = (double*)user_data;
float* out = (float*)outbuf;
printf(
"current time = %f; out time = %f\n",
time_info->currentTime,
time_info->outputBufferDacTime);
for (unsigned long i = 0; i < bufsize; i++)
{
*phase += 2 * PI * FREQ / SRATE;
out[i] = sin(*phase);
}
return 0;
}
int
main(int argc, char** argv)
{
(void)argc;
(void)argv;
PaError pa_error;
PaStream* stream = NULL;
int error = 0;
double phase = 0;
pa_error = Pa_Initialize();
if (pa_error != paNoError)
{
return 1;
}
pa_error = Pa_OpenDefaultStream(
&stream,
0,
1,
paFloat32,
SRATE,
paFramesPerBufferUnspecified,
&audio_callback,
&phase);
if (pa_error != paNoError)
{
error = 1;
goto exit;
}
pa_error = Pa_StartStream(stream);
if (pa_error != paNoError)
{
error = 1;
goto exit;
}
Pa_Sleep(DURATION);
pa_error = Pa_CloseStream(stream);
if (pa_error != paNoError)
{
error = 1;
goto exit;
}
printf("Done.\n");
exit:
Pa_Terminate();
if (pa_error != paNoError)
{
printf("PortAudio error: %s\n", Pa_GetErrorText(pa_error));
}
return error;
}
Output:
current time = 0.000000; out time = 0.000000
current time = 0.000000; out time = 0.000000
current time = 0.000000; out time = 0.000000
current time = 0.000000; out time = 0.000000
...
Addendum: This same piece of code seems to work fine with Visual Studio in Windows 10.

Answer 1

Your example compiles fine on my Mac and returns meaningful time information so the issue is not in your code.
You haven't said which audio backend you're using on Linux, but if you're using ALSA and PulseAudio, there've been problems getting time info with those (see there for instance). In this specific case of ALSA/PulseAudio, Pulse is the one to blame and PortAudio has nothing to do with that.
If you're using a different audio backend, you might want to check the implementation of the GetStreamTime() function in the corresponding src/hostapi/<your_backend> PortAudio source folder.
As a side note, never make I/O operations in an audio callback in a real product. printf is a huge function which takes quite a lot of time to execute (from an audio callback point-of-view).