Re: SCAudioFillBuffer

I too am trying to write out a QT movie using SCAudioFillBuffer, i am being handed a (video) frame and a frame's worth of uncompressed audio (44k, 16 bit big endian int, interleaved stereo)

How do I calculate how many packets to ask for, that results in exactly N bytes of uncompressed audio getting sucked thru?

for example: i need to pull exactly 2940 (uncompressed audio) samples per (video) frame (it's 15 fps).

going from what you said below:

numCompressedPackets = 2940 / asbd.mFramesPerPacket;

Unfortunately, that is a float number: 2.87109 "compressed" packets is what I apparently need to request, in order to pull out exactly 2940 uncompressed samples on this frame.

If I round up, i run out of audio before i run out of video, they're supposed to finish at the same time.

Then i think, well i'll only return 2940 samples no matter how many they ask for, yeah that'll show 'em!

But, what happens is, SCAudioFillBuffer()doesn't just return to the caller if, in my input callback, i say "i'm only going to give you 2940 samples", what happens is my input callback is called *repeatedly* until SCAudioFillBuffer() is satisfied, and THEN it returns.

Is there some setting i've missed?

should i just accumulate my audio and wait until there's at least an even multiple and THEN process it?

Begin forwarded message:

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.

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.

References:
	>RE: SCAudioFillBuffer (From: "Joe Honoroff" <email@hidden>)
	>Fwd: SCAudioFillBuffer (From: Brad Ford <email@hidden>)