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Fixing playback glitches, breakups, etc?

Posted: Sat Oct 05, 2019 4:33 pm
by wmorrison
I've been having some recordings "glitch" or "break up" during playback, that play fine when I copy the raw .ts file to my Windows PC.

One last night was "stuttering." It would flicker an image a few frames out of sync with the current time, a few times a second, mainly noticeable during pans.

For another one, the picture completely broke up to a bluish-greenish screen of "junk" for a minute or so.

I scanned that second one with ffmpeg -v error and it did find errors.

But again, both these shows played perfectly when copied to my PC, same exact file, no transcoding.

Is there a guide on how to setup up MythTV to optimize recording and playback, when "glitches" and "breakups" happen during playback?

E.g how to handle error correction? If my Windows PC can play back an mpeg stream with errors, but no noticeable glitches, I should be able to configure MythTV to do the same?

Currently, I am using VAAPI2. (VAAPI had some glitches) I believe that lets the video card do the decoding? I can try switching to software decoding and see if the affected recordings play back ok.

Re: Fixing playback glitches, breakups, etc?

Posted: Mon Oct 07, 2019 6:33 pm
by wmorrison
For the recordings that broke up to a bluish-greenish screen of "junk", switching back to VAAPI solved it. I'll have to keep an eye out for the other glitches I thought I saw with VAAPI.

For some other recordings that had "pixel noise," it seemed to play the same in software, vaapi, and vaapi2 mode. So it's probably just errors in the recording.

Re: Fixing playback glitches, breakups, etc?

Posted: Thu Oct 10, 2019 8:26 pm
by wmorrison
For the recording I said was "stuttering"...

Turns out, it's in the original recording. When I pause and play frame-by-frame, you will have several crystal-clear frames, then two or three frames together where the image appears to be a blending of two consecutive frames (blurry, with a ghost image) and then the next several frames pop back crystal clear.

It was very subtle. When watching real-time, it was like "something's wrong but I can't put my finger on it."

Since MythTV is just capturing the transport stream with no transcoding, it's not MythTV's fault.

Could the original program have been converted from one framerate to another before airing, with a filter that blends frames instead of just dropping or duplicating them?

Anyway, it's not a playback problem, so I'm done with that one.