Re: AAC options dialog 'Encoder Quality'
Re: AAC options dialog 'Encoder Quality'
- Subject: Re: AAC options dialog 'Encoder Quality'
- From: Andrea Barbieri <email@hidden>
- Date: Mon, 23 Apr 2007 09:16:41 +0100 (BST)
Hello Brad,
see below
BF:=Brad Ford
BF>
BF> On Apr 22, 2007, at 5:08 PM, Andrea Barbieri wrote:
BF>
BF> >BF:=Brad Ford
BF> >
BF> > BF> This question could be better answered on the CoreAudio list.
BF> > BF> Forwarding.
BF> > BF>
BF> > BF> -Brad Ford
BF> > BF> QuickTime Engineering
BF> > BF>
BF> > BF> Begin forwarded message:
BF> > BF>
BF> > BF> >From: Andrea Barbieri <email@hidden>
BF> > BF> >Date: April 20, 2007 6:26:59 AM PDT
BF> > BF> >To: email@hidden
BF> > BF> >Subject: AAC options dialog 'Encoder Quality'
BF> > BF> >
BF> > BF> >Hello,
BF> > BF> >
BF> > BF> >when using SoundConverter (I know I should be moving to the newer
BF> > BF> >API!) and
BF> > BF> >launching the options dialog (with title "MPEG-4 Audio Compressor")
BF> > BF> >for the
BF> > BF> >AAC component I wonder what changes when selecting the different
BF> > BF> >option
BF> > BF> >settings for Encoder Quality (Good, Better and Best).
BF> > BF> >
BF> > BF> >many thanks,
BF> > BF> >andrea
BF> > BF>
BF> >
BF> >It is interesting that Technical Q&A QA1437:
BF> >http://developer.apple.com/qa/qa2006/qa1437.html
BF> >
BF> >contains a reference to the Encoder Quality parameter, it is flagged only
BF> >as an expert parameter (not invisible) but it does not show up in the
BF> >StdAudio dialog!
BF>
BF>
BF> I can answer that one. It's a QuickTime-ie thing. The quality setting that
BF> shows up in the StdAudio dialog is not called "Encoder Quality", it's just
BF> "Quality". It corresponds to the StdAudio property
BF> kQTSCAudioPropertyID_RenderQuality:
BF>
BF> /*
BF> * kQTSCAudioPropertyID_RenderQuality: Specifies the quality with
BF> * which QuickTime should render the audio stream during the
BF> * compression/decompression/transcode operation. Accepted constants
BF> * are those used by AudioUnits (defined in AudioUnitProperties.h):
BF> * kRenderQuality_Max, kRenderQuality_High, kRenderQuality_Medium,
BF> * kRenderQuality_Low, kRenderQuality_Min. This property is available
BF> * in QT 7.1 and later.
BF> */
BF> kQTSCAudioPropertyID_RenderQuality = 'qlty', /* UInt32, Read/Write/Listen*/
BF>
BF> Render Quality is applied to sample rate conversions in the
BF> decode->mix->encode chain, and applied to codec quality on the encoder (if
BF> applicable).
BF>
BF> So when you see "Quality" in the StdAudio UI, it doesn't correspond to any
BF> setting in the settings dictionaries, but can be thought of as a superset of
BF> sample rate conversion quality + encoder quality. We then purposely
BF> suppress the "Encoder Quality" parameter in the UI. Of course if you are
BF> building your own ui from StdAudio properties, you could choose to show
BF> everything.
thanks for the explanation why the Hint flag is purposely ignored in that
example.
still, can the 'Encoder Quality' parameter be a little better explained?
many thanks,
andrea
--
Andrea Barbieri
Moving Image Research http://www.movingimageresearch.com/
The Workshop, Hampton Lane, Bristol, BS6 6LE, UK
Tel: +44 117 9732200 FAX: +44 117 9732210
PGP ID=0x034DFD5A KeyFingerprint=C168EA9A7189538D214F1281A7529F32034DFD5A
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