Fwd: SCAudioFillBuffer

Begin forwarded message:

From: Joe Honoroff <email@hidden>
Date: September 8, 2006 12:39:36 PM PDT
To: 'Brad Ford' <email@hidden>
Cc: email@hidden
Subject: RE: SCAudioFillBuffer

Yes, I have been following the scaudiocompress sample. However, when
our app publishes it sends me one video frame and that frame worth of
audio at a time, and specifies the buffer size. So for PCM output I
calculate ioOutputDataPacketSize as numPackets =
bufferSize/asbd.mBytesPerPacket which works. For Apple Lossless output
I get MaximumOutputPacketSize, but it's larger then the sound buffer I'm
given. In this case what should numPackets be?

MaximumOutputPacketSize tells you the maximum size (in bytes) that a single packet might be. In the case of Apple Lossless, if you look at the asbd, it should tell you how many pcm frames are in one packet by inspecting the mFramesPerPacket field.

I've tried numPackets =
1 but then SCAudioFillBuffer returns a PacketDescription with all the
members = 0.

I just tried "scaudiocompress -i /path/to/an_audio_file.aiff -o /path/to/a_quicktime_movie.mov -pullpackets 1

Then in the dialog, I specified Apple Lossless, and it worked perfectly. So you can definitely pull for just 1 packet of lossless at a time, if you so desire.

-Brad Ford

QuickTime Engineering

Thanks
Joe

-----Original Message-----
From: Brad Ford [mailto:email@hidden]
Sent: Thursday, September 07, 2006 12:31 PM
To: Joe Honoroff
Cc: email@hidden
Subject: Re: SCAudioFillBuffer

On Sep 7, 2006, at 12:22 PM, Joe Honoroff wrote:

Where are the error return codes defined for SCAudioFillBuffer and
QTSetComponentProperty?

I get uncompressed PCM 44100Khz, 16bit, stereo from our app and I'm
using the new SCAudioFillbuffer. I got it to work using the same
output format, but now I'm trying to ouput Apple Lossless and
SCAudioFillBuffer returns 0x77686174.

0x77686174 as a 4-char code is 'what'. A lot of CoreAudio errors are
4 character codes. In this case, look at AudioConverter.h:

kAudioConverterErr_UnspecifiedError = 'what',

So it's an unspecified error. Not very helpful, I know. It's not
clear from your description what might be going wrong. Have you
looked at the scaudiocompress sample code? It should succeed in
writing Apple Lossless.

-Brad Ford
QuickTime Engineering

And yes I am providing a a AudioStreamPacketDescription!

Thanks
Joe
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References:
	>RE: SCAudioFillBuffer (From: "Joe Honoroff" <email@hidden>)