Re: How to delay AudioQueue playing
Re: How to delay AudioQueue playing
- Subject: Re: How to delay AudioQueue playing
- From: Michael Becker <email@hidden>
- Date: Thu, 1 Oct 2009 12:39:45 +0200
Thanks for the reply! The "lag" you are talking about should be fine
for me, as long as I get the playback working. The user is not really
supposed to switch samples on or off in realtime. But I will keep
Audio Units in the back of my mind in case I will have to use them.
Here's my problem with what you suggest about the buffer: If the time
has come to "play silence" for the duration of one sample, you say, I
should either not enqueue the next buffer or play zeroes. But if I
don't call AudioQueueEnqueueBuffer, the callback is never called again
for that AudioQueue. In other words: how can I resume playback after
the one-sample-pause? My idea was to user
AudioQueueEnqueueBufferWithParameters and pass a certain
AudioTimeStamp for its starttime, but I cannot wrap my head around how
to set that timestamp. I think at that moment the "lag" you are
talking about might become a problem - the AudioQueue's timestamp I
can only get in real-time whereas the buffer playback will be sometime
in the future.
I have the gut-feeling that my simple setup (all samples are same
length and type) should make this all easier...
Regards,
Michael
Am 01.10.2009 um 02:07 schrieb Steven Winston:
AudioQueue unfortunately isn't the best way to go about doing this.
It inherently creates a queue that's buffered ahead of the PCM data
that's played. You'll notice a "lag" on anything that you alter in
your buffering callback which is what you'd expect from that type of
application. Might I recommend using AudioUnits? They'll give you
quicker feedback.
That said, here's the trick that will solve your current question of
how to play silence:
in AudioQueueServices you have a buffer callback and somewhere a call
to AudioQueueEnqueueBuffer. Don't call that when you don't want audio
from that AudioQueue to play. That or you can pass it a buffer full
of 0.
On Wed, Sep 30, 2009 at 9:06 AM, Michael Becker <email@hidden
> wrote:
Hello list, this is my first post!
I have been searching a lot on the web and in the list archives,
but I have
not found anything that helped me, although I guess that my
question has
been asked a zillion times before: I am trying to build an audio
sequencer,
i.e. an 8 track sequencer that plays audio samples. The concept is
fairly
easy: Every sample is exactly the same length, the user can only
switch
samples on or off for a complete duration.
I am using the AudioQueue API and I think I understand that I
should use one
Audio Queue for each track. So far I have managed to have two
queues loop
two samples synchronously. I basically stuck to the Apple
documentation
("Looping audio files"). It works great, they are perfectly in sync.
Now comes the problem: How do I omit individual samples during
playback? I
think the solution either comes down to "playing silence" for the
duration
of one or more samples, or delaying the playback of the next sample
for a
time that is a multiple of a sample length.
On a sidenote: Is this the right way to go about this? Or should I
somehow
create a "main clock" that ticks and only play samples according to
this
"clock"? (Instead of rigorously looping the samples back to back).
Maybe I am phrasing my question the wrong way, but please bear with
me as I
am really new to Core Audio and Sound programming in general.
Kind regards,
Michael
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