Re: AAC options dialog 'Encoder Quality'
Re: AAC options dialog 'Encoder Quality'
- Subject: Re: AAC options dialog 'Encoder Quality'
- From: Brad Ford <email@hidden>
- Date: Sun, 22 Apr 2007 18:05:55 -0700
On Apr 22, 2007, at 5:08 PM, Andrea Barbieri wrote:
BF:=Brad Ford
BF> This question could be better answered on the CoreAudio list.
BF> Forwarding.
BF>
BF> -Brad Ford
BF> QuickTime Engineering
BF>
BF> Begin forwarded message:
BF>
BF> >From: Andrea Barbieri <email@hidden>
BF> >Date: April 20, 2007 6:26:59 AM PDT
BF> >To: email@hidden
BF> >Subject: AAC options dialog 'Encoder Quality'
BF> >
BF> >Hello,
BF> >
BF> >when using SoundConverter (I know I should be moving to the
newer API!) and
BF> >launching the options dialog (with title "MPEG-4 Audio
Compressor") for the
BF> >AAC component I wonder what changes when selecting the
different option
BF> >settings for Encoder Quality (Good, Better and Best).
BF> >
BF> >many thanks,
BF> >andrea
BF>
It is interesting that Technical Q&A QA1437:
http://developer.apple.com/qa/qa2006/qa1437.html
contains a reference to the Encoder Quality parameter, it is
flagged only
as an expert parameter (not invisible) but it does not show up in the
StdAudio dialog!
I can answer that one. It's a QuickTime-ie thing. The quality
setting that shows up in the StdAudio dialog is not called "Encoder
Quality", it's just "Quality". It corresponds to the StdAudio
property kQTSCAudioPropertyID_RenderQuality:
/*
* kQTSCAudioPropertyID_RenderQuality: Specifies the quality with
* which QuickTime should render the audio stream during the
* compression/decompression/transcode operation. Accepted constants
* are those used by AudioUnits (defined in AudioUnitProperties.h):
* kRenderQuality_Max, kRenderQuality_High, kRenderQuality_Medium,
* kRenderQuality_Low, kRenderQuality_Min. This property is available
* in QT 7.1 and later.
*/
kQTSCAudioPropertyID_RenderQuality = 'qlty', /* UInt32, Read/Write/
Listen*/
Render Quality is applied to sample rate conversions in the decode-
>mix->encode chain, and applied to codec quality on the encoder (if
applicable).
So when you see "Quality" in the StdAudio UI, it doesn't correspond
to any setting in the settings dictionaries, but can be thought of as
a superset of sample rate conversion quality + encoder quality. We
then purposely suppress the "Encoder Quality" parameter in the UI.
Of course if you are building your own ui from StdAudio properties,
you could choose to show everything.
-Brad Ford
QuickTime Engineering
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