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

[Will Dormann]

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?




-WD