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

glen glenb at glenb.net
Sat Dec 25 02:19:09 UTC 2021


On Sat, 2021-12-25 at 01:25 +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?
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i would check a few things to experiment. i assume the capture (.ts
file in myth) is mpeg2 and ac3 audio .. right ?

first on a completed recording see if just changing the container does
anything. first move the finished file to a temp file: mv
(mythrecname).ts temp.ts  then run: ffmpeg -i temp.ts -vcodec copy -
acodec copy (mythrecname).ts after that check in the frontend and see
if you have the same issues.  

if you still have those issues then consider just running a transcode
job with ffmpeg when the recording completes and transcode the video to
libx264..you could do it as a user job script and just filter for the
offending channel. but first test it with

run: mv (mythrecname).ts temp.ts then run: ffmpeg -i temp.ts vcodec
libx264 -crf 24 -tune film -acodec copy (mythrecname).ts

you would probably want to customize the ffmpeg libx264 options for
deinterlace if you need etc... but it should play ok in the frontend.
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