[mythtv-users] Digital audio: centre channel drops out intermittently
Marc Sherman
msherman at projectile.ca
Mon Jan 16 02:16:31 UTC 2012
On 1/15/2012 6:26 PM, Jean-Yves Avenard wrote:
>
> You can't do upmixing 2->5 outside of myth (say using ALSA custom config).
> If that's what you are hoping to achieve it will never work as spdif
> is stereo maximum, everything more must be compressed into a digital
> stream
>
> you wrote in the previous post that upmixing was disabled in your myth
> config. I can only go by the information you provide.
It is disabled in my myth config. The only upmixing that is enabled (and
it is 2->5 upmixing) is in my JVC amp. The only reason I mentioned that
was to note that when MythTV is playing a recording with a stereo audio
track, the amp upmixes it to 5 channels and drives the centre channel
with no audible dropouts. So that establishes that the amp is capable of
sending output to the centre channel without dropouts.
The dropouts only occur when MythTV is playing a recording with a 5.1
audio track. In that situation, the centre channel drops out intermittently.
Sorry if I confused matters by describing too many different scenarios
all in one email initially.
>> Well, if myth is decoding/processing/reencoding the AC3 stream as I
>> suggested above, then it could be dropping one of the channels in this code
>> path.
>>
>
> You obviously have a clear idea of what is happening, so I'll leave you to it
No, I really don't. All I think I've done is establish that it could
possibly be a mythtv bug (possibly where it re-encodes AC3 5.1 audio),
or it could possibly be a hardware/firmware failure in my jvc amp when
it decodes the AC3 audio. I really have no idea how to proceed to
isolate this further, so I can report a proper bug or replace the broken
amp, as needed. Any suggestions would be greatly appreciated.
One thing I did try this morning is configure the frontend with
"--verbose playback,audio,libav". I then tried watching a recording that
had previously had dropouts (last night's SNL broadcast) twice back to
back, and no dropouts occurred. So either I've just got terrible luck,
or perhaps the bug was a race of some kind and the extra verbose logging
has tweaked the timings enough to avoid triggering it. :/
I'll keep an eye on it, and if it recurs, I'll check the logs to see if
anything strange shows up.
- Marc
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