[mythtv] [patch] multi channel audio patch 1
Dibblahmythml0015 at pendor.org
Fri Dec 30 14:15:51 EST 2005
Michael T. Dean wrote:
> Instead of re-encoding to AC-3, ALSA will allow 6-channel PCM output via
> the digital connection.
Not according to:
"Note that surround51 and surround40 are supposed to be analog, not for the
digital AC3/DTS. They don't decode anything. They just support the
"IEC958 was named IEC60958 at 1998. IEC60958 (The S/PDIF) can carry normal
audio and IEC61937 datastreams. IEC61937 datastreams can contain multichannel
sound like MPEG2, AC3 or DTS. When IEC61937 datastrams are transferred, the
bits which normally carry audio samples are replaced with the databits from
the datastream and the headers of the S/PDIF signal. Channel-status
information contains one bit (but 1) which tells if the data in S/PDIF frame
is digital audio or some other data (DTS, AC3, MPEG audio etc.). This bit will
tell normal digital audio equipments that they don't try to play back this
data as they were audio samples. (would sound really horrible if this happens
for some reason)."
So most decoders only support 48kHz @ (max) 24bit x 2 channels. Dividing this
down to get more channels isn't supported AND would sound nasty.
Hence why AC3, DTS etc is used as the protocol.
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