Apple

On Nov 18, 2008, at 5:27 PM, William Bates wrote:

I've been parsing CAF files that I created with ExtAudioFile, and some Apple-distributed in various sample code.

I'm doing this on an Intel machine. Everything works well as long as you are very careful about Endian-ness.

However, I note the following anomalies and would like opinions on whether the following are me, known bugs, or worth filing bug reports on:

(1) Missing channels per frame in Audio Description Chunk.

An Audio Description Chunk Data is 32 bytes, whereas the fields described should take 36 bytes:
Size of Float64 = 8
Size of UInt32 = 4
8 + 7*4 = should be size = 36
sizeof(CAFAudioDescription) = 32
ChunkSize in file = 32

I'm not sure where you are getting your info but here is the struct as defined in CAFFile.h and on this page:

http://developer.apple.com/documentation/MusicAudio/Reference/CAFSpec/CAF_spec/chapter_3_section_4.html

struct CAFAudioDescription

{

Float64 mSampleRate;

UInt32 mFormatID;

UInt32 mFormatFlags;

UInt32 mBytesPerPacket;

UInt32 mFramesPerPacket;

UInt32 mChannelsPerFrame;

UInt32 mBitsPerChannel;

} ATTRIBUTE_PACKED;

So that is 8 + 6*4 = 32 bytes. So 32 bytes is correct.

Here's a hexdump of a CAF file:

00000000 63 61 66 66 00 01 00 00 64 65 73 63 00 00 00 00 |caff....desc....|

00000010 00 00 00 20 40 e5 88 80 00 00 00 00 61 61 63 20 |... @.......aac |

00000020 00 00 00 00 00 00 00 00 00 00 04 00 00 00 00 02 |................|

00000030 00 00 00 00 6b 75 6b 69 00 00 00 00 00 00 00 27 |....kuki.......'|

...

Here's the size of the chunk, 0x20 == 32 bytes:

00000010 00 00 00 20

The channels field is the last 4 bytes on this line == 2 channels:

00000020 00 00 00 00 00 00 00 00 00 00 04 00 00 00 00 02 |................|

In practice, it seems that mChannelsPerFrame field is simply missing.

The Float64 does indeed seem to be a Float64.

References:
	>CAF file anomalies (From: William Bates <email@hidden>)