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 14:40:20 -0700
That might solve a few problems. Thanks Doug; this information should
prove to be most valuable to our application.
Thanks,
Steve
On Thu, Sep 10, 2009 at 2:35 PM, Doug Wyatt <email@hidden> wrote:
> For some preliminary context: on the phone, the hardware codec tend to take
> longer to decode but consume less power. Software codecs tend to execute
> more quickly but are more CPU and power-intensive.
>
> Software codecs are available at any time via AudioConverter, including the
> higher-level APIs which use AudioConverter -- AudioQueue and ExtAudioFile.
>
> But hardware codecs are only available via AudioQueue. (Exception: as of OS
> 3.1, you can use the AAC hardware encoder via ExtAudioFile...)
>
>
> So, if you've been using AudioQueueOfflineRender to decode and post-process
> AAC or MP3, you may want to try using AudioConverter to do a software decode
> instead.
>
> Doug
>
>
>
> On Sep 10, 2009, at 14:16 , Steven Winston wrote:
>
>> 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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