This patch series reduces the playback latency for audio backends, in some cases significantly. For PulseAudio, the audio buffer is also moved from the QEMU side to the PulseAudio server side. This improves the drop-out safety for PulseAudio.
I actually measured the latency reduction with the PulseAudio backend. For the test I used my Linux host configured to play audio with PulseAudio. The guest was a Linux guest, also configured to use PulseAudio. Measuring audio latencies is difficult. I played a sine tone in the guest with Audacity and measured the time from releasing the left mouse button until the tone can be heard. A few seconds before the measurement I started playback of an audio file with 10 minutes of silence to fill the audio buffers. The over-all latency can't be used to estimate the playback latency, but it can be used to calculate the playback latency reduction. The measured over-all latency with PulseAudio is around 200ms without these patches and around 135ms with these patches. The difference of 65ms agrees well with the expected value of 46.4ms * 2 + 15ms - 46.4ms = 61.4ms. 46.4ms * 2 is the size of the mixing-engine buffer ("[PATCH 14/15] paaudio: fix samples vs. frames mix-up" explains the factor 2), 15ms is the server side PulseAudio buffer size used before these patches and 46.4ms is the new server side PulseAudio buffer size. For JACK users these patches don't reduce the playback latency but improve drop-out safety. After patch "audio: restore mixing- engine playback buffer size" the buffer size used is exactly the same as before these patches. v2: [PATCH v2 01/15] audio: replace open-coded buffer arithmetic Replaced the audio_ring_posb macro with an inline function. The macro trick made the code quite unreadable. Compared to v1 the generated code size stays the same. [PATCH v2 06/15] jackaudio: use more jack audio buffers Improved commit message. [PATCH v2 09/15] Revert "audio: fix wavcapture segfault" Used git revert cbaf25d1f5. [PATCH v2 13/15] ossaudio: reduce effective playback buffer size Improved commit message. Volker Rümelin (15): audio: replace open-coded buffer arithmetic audio: move function audio_pcm_hw_clip_out() audio: add function audio_pcm_hw_conv_in() audio: inline function audio_pcm_sw_get_rpos_in() paaudio: increase default latency to 46ms jackaudio: use more jack audio buffers audio: copy playback stream in sequential order audio: add pcm_ops function table for capture backend Revert "audio: fix wavcapture segfault" audio: restore mixing-engine playback buffer size paaudio: reduce effective playback buffer size dsoundaudio: reduce effective playback buffer size ossaudio: reduce effective playback buffer size paaudio: fix samples vs. frames mix-up sdlaudio: fix samples vs. frames mix-up audio/alsaaudio.c | 1 + audio/audio.c | 194 ++++++++++++++++++++++++-------------------- audio/audio_int.h | 13 ++- audio/coreaudio.c | 13 +-- audio/dsoundaudio.c | 30 ++++--- audio/jackaudio.c | 5 +- audio/noaudio.c | 1 + audio/ossaudio.c | 17 +++- audio/paaudio.c | 49 ++++++----- audio/sdlaudio.c | 21 +++-- audio/wavaudio.c | 1 + 11 files changed, 203 insertions(+), 142 deletions(-) -- 2.31.1