[mythtv] [mythtv-commits] Ticket #12827: Raspberry Pi: Digital Audio does not work

Peter Bennett pgbennett at comcast.net
Wed Jul 27 19:45:06 UTC 2016

On 07/27/2016 01:40 PM, Joseph Fry wrote:
> I am no dev... but it sounds like OMX is handling the video and audio
> sync just fine... the real problem is mythtv trying to control the
> sync when it really doesn't need to.
> Is there any reason you couldn't just not check for sync at all in the
> case of pass-through?  What is the worst that would happen?  I would
> think that the audio and video are coming out of the decoder in sync,
> just push them into the render pipeline in sync and all will be well?
> Your MAXDIVERGE test suggests that the chipset does the right thing as
> long as the buffers are full.  While you seem suspicious of this, I
> would love to hear the results of some long term testing of that
> rather than an assumption that it will get out of sync eventually.  It
> may actually be the solution?
There are a couple of problems with this

1. When displaying the OSD or carrying out certain operations from the
keyboard or remote, the raspberry pi becomes overloaded and compensates
by dropping frames. This is done using the AVSync. If that is disabled,
then lip-sync will start going out if you press buttons on the keyboard.

2. With broadcast video, even digital broadcast, there are small errors
and glitches that happen from time to time. If there is nothing to sync
the audio and video these can build up and after some minutes of
watching the lip sync will likely start going off.

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