[mythtv-users] Help with playback issue on recordings from a single channel

David Engel david at istwok.net
Sat Dec 25 16:53:06 UTC 2021

On Sat, Dec 25, 2021 at 01:25:59AM +0000, Vincent Poore via mythtv-users wrote:
> I've been living with and frustrated by a problem with recordings from my local CBS broadcast channel.
> It all started when my local station added a new digital sub-channel.   I know this because my problem started on March 1st and a call to the station engineer confirmed changes were made to the broadcast signal early that Sunday morning. He says, "Everything in this encoding scheme is industry standard, so I wouldn’t expect there to be any problem decoding it with commercial equipment."  I'm not technical enough to determine what has changed that would give mythtv so much trouble.  Here are the symptoms:
> Prior to the change, I used VDPAU High Quality Video Playback Profile.   After the change, this profile on the bad channel will eventually cause my machine to lock up.  It starts with some serious macro blocking and then eventually freezes the display and I have to use power reset to recover my machine.   I discovered I am able to view the programs using Open GL High Quality.   I'm not happy about the higher CPU, but at least I can watch my programs.   However, two other bad symptoms manifest.
> After the change, the timing information of the recordings is off.   A 60 minute recording, when paused will report as 75 minutes.
> I suspect this is related to the third symptom which is that skip forward or back doesn't work properly.  The first skip forward will actually jump backward some random offset (usually 3 or 4 minutes) and then progress forward from there with repeated commands.   A skip backward does the same thing (first skip offset backwards 3 to 4 minutes).
> Note: I don't run any transcoding jobs on my recordings.   I've upgraded to Ubuntu 20.04.3 with latest mythtv patches (31.0+fixes.202111081900.25f1bb1d12~ubuntu20.04.1).
> Any suggestions?

For the lock ups, try updating your driver as was suggested.  That
shouldn't happen.

For the macroblocking, it could be the infamous, Nvidia bug that has
plagued their MPEG2 decoders for the last 10+ years.  IF that's it,
the only fix is to use software decoding (OpenGL profiles in MythTV).
Thankfully, nearly all CPUs from the last several years are powerfully
enough to do it.

David Engel
david at istwok.net

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