Re: OpenAl for streaming

Susmith,

It would be helpful if you could write a bug report to Apple and include a test program that exhibits this behavior.

thanks,
-bob aron

________________________________
Bob Aron • CoreAudio Team, Apple Inc.
[email protected]


On Jul 28, 2010, at 1:35 AM, Susmith M R (RBEI/ECF1) wrote:

> 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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