Re: [alsa-devel] first and last audio sample timestamp

25 Jun 2018


      On Mon, 25 Jun 2018 16:58:26 +0200,
Subhashini Rao Beerisetty wrote:
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On Mon, Jun 25, 2018 at 8:23 PM, Takashi Iwai tiwai@suse.de wrote:
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On Mon, 25 Jun 2018 16:50:20 +0200,
Subhashini Rao Beerisetty wrote:
...
On Mon, Jun 25, 2018 at 8:04 PM, Takashi Iwai tiwai@suse.de wrote:
...
On Fri, 22 Jun 2018 16:00:10 +0200,
Subhashini Rao Beerisetty wrote:
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[ Please keep me in CC as I'm not subscribed to the list]
Hi All,
Hello all,
I’m using aplay and arecord utilities for playback and capture. I
need to
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...
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capture the timestamps for the first and last audio samples that
arrive
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at
...
the driver level.
For this I’m capturing the CLOCK_MONOTONIC_RAW timestamp at the
.trigger(for playback & capture) callback in SNDRV_PCM_TRIGGER_START
case
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– is it the correct timestamp for the first audio sample arrived at
the
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...
driver level?
Similarly does .trigger callbacks SNDRV_PCM_TRIGGER_STOP gives the
last
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...
audio sample timestamp?
No, it's the timestamp upon calling the trigger callback.
It has nothing to do directly with the first or the last sample.
(But usually the start trigger is the time of the first sample for
 capture, though.)
Okay then if start trigger is the time of the first sample for capture,
then is stop trigger is for last sample?
No, it's not necessarily the last sample.  It's the just time you stop
the stream.  The stop might happen some time after the last sample got
received.  The accuracy in that regard pretty much depends on the
hardware and the driver implementation.
Thanks for the clarification. What about for playback scenario?
A similar situation.  The timestamp at stop trigger is the time you
stopped the stream, and it's not about the "last" sample time.
BTW, for the accurate timestamping, check
Documentation/sound/design/timestamping.rst.
Takashi
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Takashi
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For example, i'm printing the
timestamp as given below. Similarly in which call back I can use the
getrawmonotonic()
for playback case.
static int snd_mychip_capture_trigger(struct snd_pcm_substream
*substream,
...
int cmd)
{
struct timespec ts;


switch(cmd) {

    case SNDRV_PCM_TRIGGER_START:

        getrawmonotonic(&ts);

        printk("1st audio sample received time:

[%.6lu:%.9lu]\n",ts.tv_sec, ts.tv_nsec);
        break;

    case SNDRV_PCM_TRIGGER_STOP:

        getrawmonotonic(&ts);

        printk("Last audio sample received time:

[%.6lu:%.9lu]\n",ts.tv_sec, ts.tv_nsec);
        break;

}


}
...
Takashi
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