Re: 5.1 AC-3 WAVs recognized as 2 channels?
Re: 5.1 AC-3 WAVs recognized as 2 channels?
- Subject: Re: 5.1 AC-3 WAVs recognized as 2 channels?
- From: William Stewart <email@hidden>
- Date: Thu, 15 Jun 2006 12:22:10 -0700
Basically, both Dolby Digital and DTS content can (and have in the
past) masqueraded as if they are Linear PCM, 44.1KH, 16 bit stereo
source material, so that is why you see the file reporting itself
this way. There are file formats explicitly for AC-3 (its the format
Dolby uses for its AC-3 validation discs) but you don't generally see
this (rather you'd see WAVE or AIF files).
VLC is also (aside from having a decoder) going through and snooping
the bit stream to see if it is actually linear PCM data or AC-3. Once
it determines that it is, it would then pass that data to its
decoder, etc... One thing we can look at is doing some more work in
our WAVE/AIF file code to detect if the contained bit stream is
actually AC-3, so if you want to file a bug for this, that would be
appreciated.
Thanks
Bill
On 15/06/2006, at 11:21 AM, 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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