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

[Stephen Worthington]

On Thu, 13 Nov 2014 08:49:32 -0500, you 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?

I wonder if there is anything the devs can do in MythTV that might
make it able to cope with glitches like these?  It might be worthwhile
seeing if you can make a small example file that contains some
glitches and make it available to the devs (eg file a trac report with
pointers to wherever it is available from).