Hello,
The software buffer size is determined by aplay, it depends
on some default values and/or command line options, and will
have an impact on your measure if you do it this way.
Have a look at --period-time and --buffer-size.
I guess you are intending to measure the inner latency of snd_aloop,
FYI the softmixer introduces an extra delay, because it has to deal
with a copy loop, too (from snd-aloop capture, to the PCM stack
softvol+rate_converter+route+dmix+harware card).
That delay buffer is configurable, it is the "delayms" option in the HAL
json
file.
Notice that there are some things that can be done to reduce this
latency at the softmixer size, for instance mmap writes/reads have been
tested at the beginning of the project, but not validated up to now.
Best regards,
Thierry.
On 04/02/2019 06:11 AM, luop wrote:
Hello,
I understood that AGL is using the ALSA loopback driver to create a
virtual sound card to abstract underlying real sound cards. Softmixer
capture audio from the loopback in user-space, and then subsequently
playback to a real sound card.
So there must be a latency introduced. I want to measure how much this
latency is.
I recorded the time stamp that aplay invoked the snd_pcm_writei for the
first time. And recorded the time stamp that write thread in softmixer
invoked the snd_pcm_writei for the first time. The difference of these
two time stamps should be the latency introduced.
But the measurement result of latency is extremely high, which is nearly
1.4 second.
1. I am wondering that if the approach of measurement is wrong.
2. I am wondering that if anyone has measured this latency. Would it be
possible for you to share the approach and result with me?
Thank you , and I look forward to hearing from you.
Best Regards
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Neusoft Automotive Solution Business Unit
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