but why?
This changes from release to release
this is more complicated to do than you think, and I really don't have the time to go through all the details unless you can give me a good reason too (sorry, I'm not trying to be difficult, but I just don'e understand the real problem that you are trying to solve).... So, perhaps you can think about this some more, explain what your design parameters, restrictions, etc, are, and we can give you a recommendation based on that.
Thanks
On Apr 8, 2010, at 3:42 PM, McD wrote:
> Stephen,
> Thanks for the feedback. My intent is to test decoding on iPhone OS specifically. My understanding is that AAC SW decoding is more efficient than MP3 on iPhone OS.
>
> Bill,
> I plan to compare not
only AAC vs. MP3, but also other data formats like LPCM, ima4, and a-law to get a list in order of performance efficiency on iPhone OS. I also want to benchmark the AAC and MP3 SW vs HW decoding to see how big the difference will be. My test results don't seem to make sense which makes me think my test doesn't make sense. I'm comparing the CPU Time taken by my app as reported by Instruments' Activity Monitor. Is there a better way to do it?
>
> Regards,
> Paul
>
> --- On Thu, 4/8/10, William Stewart <
email@hidden> wrote:
>
> From: William Stewart <
email@hidden>
> Subject: Re: iPhone SW Decoding Performance of MP3 vs AAC
> To: "McD" <
email@hidden>
> Cc: "CoreAudio API" <
email@hidden>
> Date: Thursday, April 8, 2010, 4:14 PM
>
> Unless you really really need to be concerned about this, I would use the format that best suits your needs - by and large, AAC decoding will be more efficient in our implementations than MP3
>
> Bill
>
> On Apr 8, 2010, at 11:56 AM, Stephen Davis wrote:
>
> > Your test isn't really meaningful in the context of your opening statement.
> >
> > The statement that AAC decoding "should" be more efficient than MP3 is only relevant if the two SW decoders have received the same level of optimization tweaks. In other words, a plain vanilla AAC decoder will obviously be more expensive
than a highly optimized MP3 decoder even though the latter's compression algorithm might indicate that it *should* be more expensive.
> >
> > I have no knowledge of the implementation details on the iPhone but it's certainly possible that most of the optimization work has been done on the hw-accelerated path for AAC decoding since that is the common case. In other words, it is perfectly reasonable for the SW AAC decoder to be less efficient than the SW MP3 decoder on iPhoneOS.
> >
> > What you have compared is two specific SW implementations, not the complexity of the compression algorithms.
> >
> > hth,
> > stephen
> >
> > On Apr 8, 2010, at 11:43 AM, McD wrote:
> >
> >> Sorry. I meant decoding. Everything I wrote relates to decoding. No encoding was done. Any ideas?
> >>
> >> --- On Thu,
4/8/10, James McCartney <
email@hidden> wrote:
> >>
> >> From: James McCartney <
email@hidden>
> >> Subject: Re: iPhone SW Decoding Performance of MP3 vs AAC
> >> To: "McD" <
email@hidden>
> >> Cc:
email@hidden> >> Date: Thursday, April 8, 2010, 1:15 PM
> >>
> >>
> >>> My understanding is that AAC should be more efficient than MP3 for SW decoding.
> >>> ...
> >>> However,
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