Re: Accessing audio samples from Audio Queue Buffers
Re: Accessing audio samples from Audio Queue Buffers
- Subject: Re: Accessing audio samples from Audio Queue Buffers
- From: Steven Winston <email@hidden>
- Date: Thu, 10 Sep 2009 14:16:53 -0700
So Doug, This means that we'd be using the 'software' decoders and
not the 'hardware' decoders? So there's really no benefit towards not
including a software decoder library as it's not really going to the
hardware decoder, then providing PCM back to the OS prior to sending
it to the DAC?
Have a feeling you can't answer this in its' entirety so just a quick
explanation about what's available would be most helpful.
Thanks,
Steve
On Thu, Sep 10, 2009 at 2:12 PM, Doug Wyatt <email@hidden> wrote:
> Oops, I was just reminded that we *do* have a software MP3 decoder as of
> 3.0. I don't know what I was thinking.
>
> sorry for the confusion
> Doug
>
> On Sep 10, 2009, at 13:55 , Doug Wyatt wrote:
>
>> The new capability in 3.1 is to be able to use the hardware AAC *encoder*,
>> *only* ... nothing has changed with respect to hardware decoders. We do have
>> some software decoders available as of 3.0, but MP3 isn't one of them.
>>
>> As for the difference in MP3 decode rates, that's interesting. If you
>> like, file a bug and attach files which illustrate the problem and we'll
>> investigate.
>>
>> thanks,
>> Doug
>>
>> On Sep 9, 2009, at 17:43 , Steven Winston wrote:
>>
>>> Well in my tests I'm noticing that some audio when encoded with the
>>> exact same format are filling the audioqueueofflinerender buffers at
>>> different rates than other files encoded with the same format. I
>>> didn't investigate too far into this however, it seems like there must
>>> be some overhead that prevents the callback happening at a more
>>> consistant rate between the files.
>>>
>>> So for instance if file A is encoded as a MP3 44.2 khz 16 bit 2 chan
>>> file and file B is also encoded as a MP3 44.2 khz 16 bit 2 chan file
>>> when they are decoding file A might decode at an appreciable rate
>>> slower than file B when using AudioQueueOfflineRender. If that
>>> problem doesn't exist, in the ExtAudioFile, then I can scrap the
>>> external software MP3 decoder in my project.
>>>
>>> On Wed, Sep 9, 2009 at 5:33 PM, William Stewart<email@hidden> wrote:
>>>>
>>>> On Sep 9, 2009, at 5:28 PM, Steven Winston wrote:
>>>>
>>>>> That's awesome! However, a question, is this solution going to suffer
>>>>> from the same different files of the exact same format decode at
>>>>> different rates problem?
>>>>
>>>> "same different" - sorry, but I don't understand the problem you are
>>>> referring too.
>>>>
>>>>> I'll start digging through 3.1 docs and will
>>>>> eagerly await the further details.
>>>>>
>>>>> On Wed, Sep 9, 2009 at 5:22 PM, William Stewart<email@hidden> wrote:
>>>>>>
>>>>>> One of the new things in iPhone OS 3.1 is that you can use
>>>>>> ExtAudioFile
>>>>>> to
>>>>>> read and write compressed data where you may need to use a hardware
>>>>>> assisted
>>>>>> codec (such as AAC encoding) to do so.
>>>>>>
>>>>>> Details are forthcoming, including some example code - have a look in
>>>>>> the
>>>>>> tech notes and release notes for the 3.1 release
>>>>>>
>>>>>> Bill
>>
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