[mythtv] Ticket #13446: Android Digital Audio

Peter Bennett pb.mythtv at gmail.com
Tue May 21 02:57:34 UTC 2019

On 5/20/19 6:01 PM, MythTV wrote:
> #13446: Android Digital Audio
> -----------------------------+-------------------------------
>   Reporter:  Peter Bennett    |          Owner:  Peter Bennett
>       Type:  Developer Task   |         Status:  assigned
>   Priority:  minor            |      Milestone:  unknown
> Component:  Ports - Android  |        Version:  Unspecified
>   Severity:  medium           |     Resolution:
>   Keywords:                   |  Ticket locked:  0
> -----------------------------+-------------------------------
> Comment (by mspieth):
>   My understanding is that there is no digital passthrough working at all
>   ATM since GetOutputSettings does not report as such. I removed the
>   DISABLE_AC3_ENCODE define and no difference in functionality as expected.
>   I can see how to do passthrough though. There are modes available such as
>   ENCODING_AC3 which accept compressed digital streams, just set the bitrate
>   correctly and pass the ac3 stream as encoded/reencoded and everything
>   *SHOULD* just work.
>   I have not check the patches yet so you might have done this already and
>   it didnt work.
Hi Mark

I thought it better to conduct the conversation via email rather than in 
the ticket.

I have an Onkyo amplifier with optical input, no HDMI. What I do with my 
viewing of MythTV is send the audio and video to the TV HDMI port. Then 
I have an optical cable from the TV to the amplifier.

With linux version of MythTV, I select digital capabilities Dolby 
Digital, and it gets through to my amplifier where I see "Dolby Digital" 
displayed on the Onkyo screen. This setup works for AMD64 frontend as 
well as raspberry pi frontend.

This setup cannot support multi-channel LPCM since optical cables are 
not able to support that.

When I connect either the fire stick or the Shield to the TV in this 
setup, and select AudioTrack, enabling the Dolby Digital checkbox, I 
also get Dolby Digital displayed on the Onkyo. From this I conclude it 
is passing through.

The interesting thing is that if I connect the fire stick to an HDMI 
monitor, which does not support AC3, I still get sound from the monitor, 
in stereo. It seems that android is deciding correctly that my monitor 
cannot support AC3 and is decoding for me. I believe that is what the 
"automatic" setting in android does. (Note that with the HDMI monitor if 
I do that with linux I get no sound).

Perhaps in your case the android decides correctly that your TV supports 
multi-channel LPCM and it decides to use that? Or incorrectly decides 
that your TV does not support AC3 and uses LPCM?

There is an advanced audio setting in MythTV called "Stereo PCM only" I 
have that set so that it does not attempt multi-channel LPCM. Have you 
tried setting that?

I may be completely off base here, and somebody with a multi channel 
LPCM capable system will need to check that part of it.

I am not sure what change you are recommending. I know the channel 
assignment is incorrect as you have pointed out, and I will fix that, 
but I don't know if that will fix your problems.

I will be away for two weeks starting next week, so I won't be making 
any major changes before that. If you have a fix before I get back, feel 
free to commit it.


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