Replacing QuickTime with OpenAL

[Petr Mikšík]

Dear list members,

 

we develop an application which heavily uses QuickTime for audio playback. With Windows Vista, QuickTime, as still based on DirectSound, stopped to be hardware accellerated and cracks appear in the mixed sound output. Besides that, as of QuickTime 7.4, a very significant slowdown could be observed. We have finally decided to ditch QuickTime and use OpenAL, which seems to be a good replacement.

 

Reading OpenAL manual and thinking about the new app's structure, we have found difficulty in getting sound samples as our application either plays the audio back or exports mixed audio into a file (currently WAV, and AAC). We have read about capture device extension but are not sure if this is a way to go and what to do if this extension is NOT present (or at least it seems that it could be missing).

 

How do we get audio samples after they get mixed so we could stream them into a file?

 

Best Regards,

 

  Petr Miksik

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[Thomas husbyn]

---------- Forwarded message ----------
From: Petr Mikšík <petr.miksik@...>
Date: Thu, Jun 5, 2008 at 2:28 PM
Subject: [Openal] Replacing QuickTime with OpenAL
To: openal@...

Dear list members,

 

we develop an application which heavily uses QuickTime for audio playback. With Windows Vista, QuickTime, as still based on DirectSound, stopped to be hardware accellerated and cracks appear in the mixed sound output. Besides that, as of QuickTime 7.4, a very significant slowdown could be observed. We have finally decided to ditch QuickTime and use OpenAL, which seems to be a good replacement.

 

Reading OpenAL manual and thinking about the new app's structure, we have found difficulty in getting sound samples as our application either plays the audio back or exports mixed audio into a file (currently WAV, and AAC). We have read about capture device extension but are not sure if this is a way to go and what to do if this extension is NOT present (or at least it seems that it could be missing).

 

How do we get audio samples after they get mixed so we could stream them into a file?

 

Best Regards,

 

  Petr Miksik

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--
Mvh Thomas husbyn


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[Chris Robinson-5]

On Thursday 05 June 2008 05:28:07 am Petr Mikšík wrote:
> Reading OpenAL manual and thinking about the new app's structure, we have
> found difficulty in getting sound samples as our application either plays
> the audio back or exports mixed audio into a file (currently WAV, and AAC).
> We have read about capture device extension but are not sure if this is a
> way to go and what to do if this extension is NOT present (or at least it
> seems that it could be missing).

The capture extension is likely present on any implementation so long as the
hardware supports capture. That should work fine as long as your card is set
up to capture output. Open a playback device, open a capture device, then
capture samples regularly as you use the playback device normally.

Another possibility is to use OpenAL Soft
<http://kcat.strangesoft.net/openal.html>, which has a Wave File Writer
device built-in, that writes the mixed output to a standard .wav file (named
in alsoft.ini in the ApplicationData path;see the packaged alsoftrc.sample
for more info). If the app is expected to be distributed with that
capability, the capture method would be more reliable since Windows users
won't likely have OpenAL Soft.

As for converting to AAC, you can probably use something like FFMPEG, or
DirectShow, to encode a wave stream into AAC. I've never tried, though, so I
don't know what would be involved.

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[Jason Daly]

Chris Robinson wrote:

On Thursday 05 June 2008 05:28:07 am Petr Mikšík wrote:
  

The capture extension is likely present on any implementation so long as the
hardware supports capture. That should work fine as long as your card is set
up to capture output. Open a playback device, open a capture device, then
capture samples regularly as you use the playback device normally.
  

This is tricky, though.  You first have to have hardware that supports capture of the PCM channel.  I know Creative cards typically support this, but in my experience, most on-board sound chips don't.  Typically, you can only capture from the ADC channels (mic or line).  They probably do this because it's easy for a novice user to set up a feedback loop between an input and the PCM channel.

Even on hardware that supports it, you have to be sure that the PCM channel is selected for capture, and OpenAL has no control over this.

Like Chris said, if this app is only used internally, you're probably fine with using OpenAL-Soft and the "wave" backend.  If you're shipping this application, there might not be an adequate solution for you in OpenAL land.


--"J"

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[Dan Peacock-2]

Also - just a FYI ... on cards that do have the ability to capture
their own output (on Creative boards this feature is called
"What-U-Hear") ... this is *all* the audio output from the system -
not just one particular application.  i.e. If you are playing music
with WMP at the same time as your application, you will capture that
too.

Dan

On 6/5/08, Jason Daly <jdaly@...> wrote:
> Chris Robinson wrote:
> On Thursday 05 June 2008 05:28:07 am Petr Mikšík wrote:

> The capture extension is likely present on any implementation so long as
> the
hardware supports capture. That should work fine as long as your card is
> set
up to capture output. Open a playback device, open a capture device,
> then
capture samples regularly as you use the playback device normally.

>
> This is tricky, though.  You first have to have hardware that supports
> capture of the PCM channel.  I know Creative cards typically support this,
> but in my experience, most on-board sound chips don't.  Typically, you can
> only capture from the ADC channels (mic or line).  They probably do this
> because it's easy for a novice user to set up a feedback loop between an
> input and the PCM channel.
>
> Even on hardware that supports it, you have to be sure that the PCM channel
> is selected for capture, and OpenAL has no control over this.
>
> Like Chris said, if this app is only used internally, you're probably fine
> with using OpenAL-Soft and the "wave" backend.  If you're shipping this
> application, there might not be an adequate solution for you in OpenAL land.
>
>
> --"J"
>
> _______________________________________________
> Openal mailing list
> Openal@...
> http://opensource.creative.com/mailman/listinfo/openal
>
>

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[Stefanos A.]

There is nothing stopping you from distributing OpenAL Soft with your application. If you don't use EFX effects, your users won't lose any significant functionality compared to the OpenAL implementation shipped with the audio card's drivers.

On 6/6/08, Dan Peacock <danthelegoman@...> wrote:

Also - just a FYI ... on cards that do have the ability to capture
their own output (on Creative boards this feature is called
"What-U-Hear") ... this is *all* the audio output from the system -
not just one particular application.  i.e. If you are playing music
with WMP at the same time as your application, you will capture that
too.


Dan


On 6/5/08, Jason Daly <jdaly@...> wrote:
> Chris Robinson wrote:
> On Thursday 05 June 2008 05:28:07 am Petr Mikšík wrote:

> The capture extension is likely present on any implementation so long as
> the
hardware supports capture. That should work fine as long as your card is
> set
up to capture output. Open a playback device, open a capture device,
> then
capture samples regularly as you use the playback device normally.

>
> This is tricky, though.  You first have to have hardware that supports
> capture of the PCM channel.  I know Creative cards typically support this,
> but in my experience, most on-board sound chips don't.  Typically, you can
> only capture from the ADC channels (mic or line).  They probably do this
> because it's easy for a novice user to set up a feedback loop between an
> input and the PCM channel.
>
> Even on hardware that supports it, you have to be sure that the PCM channel
> is selected for capture, and OpenAL has no control over this.
>
> Like Chris said, if this app is only used internally, you're probably fine
> with using OpenAL-Soft and the "wave" backend.  If you're shipping this
> application, there might not be an adequate solution for you in OpenAL land.
>
>
> --"J"
>

> _______________________________________________
> Openal mailing list
> Openal@...
> http://opensource.creative.com/mailman/listinfo/openal
>
>

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[Jason Daly]

StApostol wrote:
>
> There is nothing stopping you from distributing OpenAL Soft with your
> application. If you don't use EFX effects, your users won't lose any
> significant functionality compared to the OpenAL implementation
> shipped with the audio card's drivers.
>

That's certainly true.  The question is whether that will provide enough
of a solution.  Using the wave backend could certainly work, but it
might be too cumbersome to be practical in a real-world application.

--"J"
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