HD homerun breaks up for one second (or less) on only one channel

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HD homerun breaks up for one second (or less) on only one channel

Post by kr_emerson » Tue Nov 19, 2019 3:30 am

I have 2 HDHR tuners: a quttro and a dual. All programming is OTA. All recordings are perfect except for 1 channel (NBC). Watching recordings from this channel breaks up for 1 second or less whenever there is a large change in the picture like when the broadcast throws up an ID banner for the news program. It's as if the stream is missing a type 'A' frame so it pixelates until it gets the next A frame.

So I have experimented as follows:
Check signal with HDHR app: 100% for all three measurements
use all the tuners (total of 6) -- all have the problem
Connect a different antenna: same problem
Disable commercial flagging: same problem
Connect antenna to TV (live-no mythtv): perfect picture
Use smart TV's software to connect directly to HDHR: perfect picture

This tells me something is happening while reading/writing the stream by the backend. I'm running v30 on Ubuntu 16.4. None of the other channels exhibit this behavior. The problem is definitely in the recording and not the playback.

The recordings aren't unwatchable, just (very) annoying. I don't know what else to try. Does anyone have any ideas?

-- Ken Emerson

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Joined: Sun Jun 15, 2014 1:08 am

Re: HD homerun breaks up for one second (or less) on only one channel

Post by blm-ubunet » Wed Nov 20, 2019 11:13 pm

I don't agree with your conclusion altho you might be right.
Big changes in picture are typically accompanied by keyframes in program stream files (BD etc).
But I believe ATSC OTA broadcast uses more complex keyframe/refresh methods.

If you play the recording file with mpv (not MythTV) & you have the glitch then the problem is with recording the data stream to disk/file.
If not then I would suspect MythTV video decoding engine.

H264 or MPEG2 video ?
Video decoding using VDPAU, VAAPI or ffmpeg (CPU) ?
Sample video (cut with 'dd')

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