Re: SPDIF encoded output on G5
Re: SPDIF encoded output on G5
- Subject: Re: SPDIF encoded output on G5
- From: Derk-Jan Hartman <email@hidden>
- Date: Thu, 1 Dec 2005 01:09:27 +0100
Incorrect. You need to byte-swap as dictated by the flags.
Natively, an AC-3 bitstream has the same endian properties as MPEG
data streams. That is, it's big endian. When you take the native
stream and hack it up to be put on a SPDIF cable (which is what
kAudioFormat60958AC3 signifies), you are basically making the AC-3
packet behave like 16 bit, stereo, signed integer data (which is
why the standard format flags apply to the ASBD).
So, if the ASBD sets kAudioFormatFlagIsBigEndian, you don't need
to byte-swap. If kAudioFormatFlagIsBigEndian is clear, you have to
byte-swap the data as if it was 16 bit samples.
mm, ok.
This is extraordinary in my eyes. I have not seen a device so far
that has big endian set for SPDIF output in HAL or Alsa.
In this case does the SPDIF header have to be byteswapped as well ?
Answer to self,
YES you do.
I made some changes to the VLC framer to output big endian, and now
it works !!!!!
wohooo. the question now is how i nicely integrate this into the VLC
architecture. Alsa is always LE as far as i know, but from DirectX
i'm no so sure. Depending on the commonness of this i will either
byteswap back in IOProc or introduced spdif_LE and spdif_BE. but
that's for tomorrow.
Finally after all this time, VLC will be able to support digital
audio and discrete multichannel audio in one application. :D It took
a while, but we are finally there :D
DJ
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