Having worked some with AC-3 I can answer a few questions here.
AC3's header contains all the sample and channel information, so it
can effectively ignore the information provided by the container. In
may ways, it is just like an MPEG stream format.
Some good news for you: I have recently fixed and release a core-
audio decoder for AC3 (http://trac.cod3r.com/a52codec). It is
capable of multi-channel decoding up to 5.1. In addition, I have
written a quicktime importer to read the .ac3 file format, but this
is available only through the source in subversion. I downloaded
the .ac3 file you listed (not the wav) and it works perfectly fine
within this decoder/importer. With the importer, you can save a .mov
(reference or otherwise) and it will serve as a complete container
format for the audio. Now, none of this does passthrough to a
decoder, so in order to enjoy surround sound, you must have an audio
device with enough discrete channels. Also, you can use QT or core
audio to export to another format if you like.
On Jun 15, 2006, at 1:21 PM, Stephen F. Booth wrote:
Hello all,
I recently downloaded a 5.1 AC-3 sample WAV from http://
www.kellyindustries.com/sounds.html
Background: Opening the file with QuickTime Player results in
static- the file is shown as stereo. However, VLC correctly opens
and plays the file.
If I open the file with ExtAudioFileOpen(), and then get
information using ExtAudioFileGetProperty(), the resulting
AudioStreamBasicDescription is filled in with 44.1 kHz, 2-channel
audio at 16 bits per sample. Obviously any operations performed on
the 5.1 file treating it as 2 channels result in audio garbage (I
primarily want to convert to FLAC).
The WAVE header looks like (starting at the 'fmt ' chunk): 66 6D 74
20 10 00 00 00 01 00 02 00 44 AC 00 00 10 B1 02 00 04 00 10 00.
With this header, the Core Audio interpretation seems to be
correct- the header implies 2-channel audio (I referred to the WAVE
header info at http://ccrma.stanford.edu/courses/422/projects/
WaveFormat/).
I couldn't find any information on 5.1 WAVE format, but assuming
the same as regular WAVE, I am stumped how this file plays
correctly in VLC but generates static in QuickTime Plyaer. Have I
done something wrong or does Core Audio not support this type of WAV?
Thanks,
Stephen
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