[mythtv-users] AC3 passthrough not working

[Allen Edwards]

On Fri, Apr 10, 2009 at 9:09 AM, Glenn Sommer <glemsom at gmail.com> wrote:

> Hey
>
> I'm trying to get AC3 / DTS passthrough to work in MythTV 0.21-fixes.
>
> This is what I've done sofar.
>
> 1. Tested the SPDIF output works using mplayer (mplayer -ac
> hwa3c,hwdts -ao alsa:device=hw=0.1)
>
> 2. Configured MythtTV:
> Audio output device = ALSA:default
> Passthrough output device = ALSA:iec958( AES0 0x02 )
> Max Audio Channels = Stereo
> Upmix = Passive
> Enable AC3 to SPDIF passthrough = checked box
> Enable DTS to SPDIF passthrough = Checked box
> Aggressive Sound Card = Not checked box
> Use internal volume control = Not checked box
>
> (All other channels NOT using AC3 or DTS are working fine over spdif)
>
> aplay -L says:
> mythtv at mediecenter ~ $ aplay -L
> default:CARD=Intel
>     HDA Intel, ALC888 Analog
>     Default Audio Device
> front:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     Front speakers
> surround40:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     4.0 Surround output to Front and Rear speakers
> surround41:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     4.1 Surround output to Front, Rear and Subwoofer speakers
> surround50:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     5.0 Surround output to Front, Center and Rear speakers
> surround51:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     5.1 Surround output to Front, Center, Rear and Subwoofer speakers
> surround71:CARD=Intel,DEV=0
>     HDA Intel, ALC888 Analog
>     7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
> null
>     Discard all samples (playback) or generate zero samples (capture)
>
> aplay -l says:
> mythtv at mediecenter ~ $ aplay -l
> **** List of PLAYBACK Hardware Devices ****
> card 0: Intel [HDA Intel], device 0: ALC888 Analog [ALC888 Analog]
>   Subdevices: 1/1
>   Subdevice #0: subdevice #0
> card 0: Intel [HDA Intel], device 1: ALC888 Digital [ALC888 Digital]
>   Subdevices: 1/1
>   Subdevice #0: subdevice #0
>
> 3. I've ensured no /etc/asound.conf or ~/.asound.conf files exist!
>
> When trying to watch something containing AC3, I shortly see my
> receiver says Dolby Digital... By looking at my receiver - it seems
> that it knows an AC3 stream is there, but it contains 0 channels (my
> receiver shows the channels in use, and all channels are off when
> using MythTV).
>
> When using mplayer everything works as expected.
>
> Clearly I must have missed something obivios here - I just cannot
> figure out what?
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>


Why on earth would you want to resample.  The goal should bit true digital
output.  Pass the bits to the receiver and let it do a DAC.  For best
quality, don't decode, encode, decode just decode.

Allen
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