[alsa-devel] first and last audio sample timestamp

[Subhashini Rao Beerisetty]

On Mon, Jun 25, 2018 at 8:23 PM, Takashi Iwai <tiwai at suse.de> wrote:

> 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 at suse.de> wrote:
> >
> > > On Fri, 22 Jun 2018 16:00:10 +0200,
> > > Subhashini Rao Beerisetty wrote:
> > > >
> > > > [ 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
> > > > capture the timestamps for the first and last audio samples that
> arrive
> > > 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
> > > > – is it the correct timestamp for the first audio sample arrived at
> the
> > > > driver level?
> > > >
> > > > Similarly does .trigger callbacks SNDRV_PCM_TRIGGER_STOP gives the
> last
> > > > 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?


>
>
> Takashi
>
> > 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
> > >
>