RE: OpenAl for streaming

Thanks for your reply
I am not using alBufferDataStatic. My problem is, when I use alSourceUnqueueBuffers, I am getting the same Unqueued bufferid again. Why it is happening? This changes the state of my program.

One more question.
Can I use alSourceUnqueueBuffers while some buffer is playing. When I used like this sometimes I am getting AL_INVALID_VALUE. Why is this? How do we know the buffer id of the processed buffers?
I am using
                        alGetSourcei( m_nALOalSource, AL_BUFFERS_PROCESSED, &iBuffersProcessed );
To get the no of buffers processed and using the following loop to unqueue
                       while ( iBuffersProcessed )
                        {
                            uiBuffer = 0;
                            alSourceUnqueueBuffers( m_nALOalSource, 1, &uiBuffer );
                                    bCheckPrintALErrorString("alSourceUnqueueBuffers")
                            iBuffersProcessed--;
                        }
I am not sure why alSourceUnqueueBuffers is returing AL_INVALID_VALUE. In the document it is specified that alSourceUnqueueBuffers will only return AL_INVALID_VALUE when "At least one buffer can not be unqueued because it has not been processed yet.". From the above code how is that possible since I am only unqueueing iBuffersProcessed from the processed queue.


Best Regards
 Susmith MR

-----Original Message-----
From: Eric Wing [mailto:[email protected]]
Sent: Wednesday, 28. July 2010 12:20 PM
To: Susmith M R (RBEI/ECF1)
Cc: [email protected]
Subject: Re: [Openal] OpenAl for streaming

On 7/27/10, Susmith M R (RBEI/ECF1) <[email protected]> wrote:
> Hi everyone,
>
> I am developing an OpenAL based application for iPhone.
>
> When I use alSourceUnqueueBuffers in a loop I get the same unqueued BufferID
> for the immediately-next alSourceUnqueueBuffers command. Since I am using a
> bufferID list to reuse the bufferIDs for my application, there is no need to
> recreate or delete the buffers. I have already created a set of buffers
> during the initialization of my application. After unqueuing the buffer from
> the OpenAl queue I use the unqueued bufferIDs to fill new buffer data using
> albufferdata and then queue it to OpenAL. I don't know when exactly the
> buffer will be freed. Please refer
> http://old.nabble.com/Why-does-alDeleteBuffers-gives-a-AL_INVALID_OPERATION-error--td22632832.html.
> Can this result in any internal conflict in OpenAL state? alBufferData and
> alSourceQueueBuffer are not returning any error.
>
> Is there any way to know the completion of the command
> alSourceUnqueueBuffers?
>

Reusing the buffer is fine. I think of it like malloc and free. You
use malloc to allocate a block of memory. You write over and over
again to that same block of memory for reuse. But when you are finally
done, you need to free that block of memory.

If you stick to standard OpenAL, I don't think you need to expect
alSourceUnqueueBuffers to have a race condition unless Apple has a
bug, in which case you should file a bug report. However, if you are
using the iPhone OpenAL extension, alBufferDataStatic, then you have
to worry about alDeleteBuffers failing. It is not just limited to
alSourceUnqueueBuffers either. alDeleteBuffers will be your pinch
point. You will need to call alDeleteBuffers and check alGetError() to
see if it failed (because Apple overloaded the function for this
case). Then you must react accordingly (after the fact) if there is a
failure.

Or you could avoid using the alBufferDataStatic extension.


I highly recommend my book, "Beginning iPhone Games Development" in
which I extensively cover OpenAL. Coincidentally, the longest chapter
in the book is on audio streaming and there is a full blown OpenAL
implementation that includes streaming. I also spend considerable
energy explaining the sharp knives associated with the
alBufferDataStatic extension on iOS. (The Creative/Xbox implementation
which also offers the extension is apparently immune to these
problems.)

http://playcontrol.net/iphonegamebook/

-Eric

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