Fix latency compensation for audio data in portaudio backend

For drivers that correctly report latency values(ASIO) this should result a
much closer alignment of audio in a loopback test. Measurement and
adjustment may still be needed, especially for non-ASIO drivers.

Testing with the RME HDSP Multiface and Yamaha AG06 using ASIO drivers results
in maximum offset of a couple of samples.

diff --git a/libs/backends/portaudio/portaudio_backend.cc b/libs/backends/portaudio/portaudio_backend.cc
index 56e5caf8a2344b6965d6014106a7eae45b9f3ab5..8443da256a6f7ccf135e2ccd2213556271d8eb34 100644 (file)
--- a/libs/backends/portaudio/portaudio_backend.cc
+++ b/libs/backends/portaudio/portaudio_backend.cc
@@ -1242,12 +1242,19 @@ PortAudioBackend::register_system_audio_ports()
        const uint32_t a_ins = _n_inputs;
        const uint32_t a_out = _n_outputs;
 
-       // XXX PA reported stream latencies don't match measurements
-       const uint32_t portaudio_reported_input_latency =  _samples_per_period ; //  _pcmio->capture_latency();
-       const uint32_t portaudio_reported_output_latency = /* _samples_per_period + */ _pcmio->playback_latency();
+       uint32_t capture_latency = 0;
+       uint32_t playback_latency = 0;
+
+       // guard against erroneous latency values
+       if (_pcmio->capture_latency() > _samples_per_period) {
+               capture_latency = _pcmio->capture_latency() - _samples_per_period;
+       }
+       if (_pcmio->playback_latency() > _samples_per_period) {
+               playback_latency = _pcmio->playback_latency() - _samples_per_period;
+       }
 
        /* audio ports */
-       lr.min = lr.max = portaudio_reported_input_latency + (_measure_latency ? 0 : _systemic_audio_input_latency);
+       lr.min = lr.max = capture_latency + (_measure_latency ? 0 : _systemic_audio_input_latency);
        for (uint32_t i = 0; i < a_ins; ++i) {
                char tmp[64];
                snprintf(tmp, sizeof(tmp), "system:capture_%d", i+1);
@@ -1260,7 +1267,7 @@ PortAudioBackend::register_system_audio_ports()
                _system_inputs.push_back (audio_port);
        }
 
-       lr.min = lr.max = portaudio_reported_output_latency + (_measure_latency ? 0 : _systemic_audio_output_latency);
+       lr.min = lr.max = playback_latency + (_measure_latency ? 0 : _systemic_audio_output_latency);
        for (uint32_t i = 0; i < a_out; ++i) {
                char tmp[64];
                snprintf(tmp, sizeof(tmp), "system:playback_%d", i+1);