[mythtv-users] HD-PVR dropped frames / MythTV AV glitches

[Andrew C. (AFPup) Stadt]

On 14-11-13 08:49 AM, Will Dormann wrote:
> On 11/11/14 9:13 AM, Will Dormann wrote:
>
>> 2) The cable box (Comcast Motorola 6200) is actually emitting video with
>> occasional dropped frames.  And that glitch is cascading through the
>> chain of MythTV, VDPAU, Pluseaudio, SPDIF, digital audio receiver, etc.,
>> to the point where it's noticeable.
>
> Just to close the loop here...
>
> The above scenario is exactly what is going on here.   I verified this
> by completely bypassing the MythTV setup and just watching TV directly
> from the cable box to the TV, just like the unwashed masses.  :)
> Every now and then, there's an AV glitch.   Sometimes barely noticeable,
> and sometimes enough that there's a visual glitch along with it.
>
> When the HD-PVR is recording S/PDIF (passthrough) the glitch appears to
> cascade, and ends up with audio being out of sync, and then MythTV
> correcting.   However, when set up to re-encode analog audio, the HD-PVR
> minimizes the impact of the glitch, and the resulting stream will at
> least not have AV sync issues.   Though will still obviously retain any
> visual glitch artifacts emitted by the cable box, if there are any.
>
> The compromise of recording analog audio is just that.  A compromise.
> The problem that resulted in the symptoms that I was seeing originated
> outside of the whole chain of MythTV components; perhaps surprisingly to
> me at least.
>
> As suggested elsewhere in the thread, it's possible that a different
> cable box may not have the same problem.   But then again, maybe it
> will.  What if the occasionally-glitchy video is not internal to the
> cable box, but rather an artifact of having a sub-par signal to the
> cable box?  e.g. because of sub-par cabling or related components
> somewhere along the way.   Or perhaps even the local Comcast head-end is
> sending out imperfect video?
>
>
This might be just a shot in the dark here, but I was having some hd-pvr 
issues and ended up going back to analogue audio for awhile, which 
seemed to fix most of my issues. A couple weeks later I had some extra 
time to kill and reconnected the spdif... issues returned.  On a whim, 
swapped out the optical audio cable, and my issues resolved.  Never 
figured out exactly what was wrong with the cable... just tossed it.