[mythtv-users] V31 software playback Double rate de-interlacer causing audio to go out of step

[John]

Raised as https://code.mythtv.org/trac/ticket/13629#ticket



-------- Forwarded Message --------
Subject: 	V31 software playback Double rate de-interlacer causing audio 
to go out of step
Date: 	Tue, 2 Jun 2020 16:25:57 +0100
From: 	John <jksjdevelop at gmail.com>
To: 	Discussion about MythTV <mythtv-users at mythtv.org>



There have been a few mentions here that the double rate de-interlacer 
can cause large shifts in audio and juddery playback when using ffmpeg 
for playback.

Platform Intel Ubuntu

The issue does not occur with VDPAU NVDEC or VAAPI.

This issue was not present in early versions of V31.

I tried to bisect it today but not being a developer may have got it 
wrong , the bisect however did land on a likely candidate.

commit 31c68a14e816df1ff256280821aeaf8e5f14610d (refs/bisect/bad)
Author: Mark Kendall <mark.kendall at gmail.com>
Date:   Tue Mar 10 20:50:03 2020 +0000

     MythDeinterlacer: Don't cleanup deinterlacer if already deinterlaced

     (cherry picked from commit 62a8f70bcb6aa1015f545808e3b9007666b6dbb8)

--a quote from another website explaining the dynamics.

The problem occurs with UK DVB-T2 streams which use on-the-fly dynamic 
progressive / interlaced encoder switching.
These channels dynamically switch the broadcast encoders between 1080p25 
and 1080i25 (i.e. actually switch the encoder from progressive to 
interlaced) on a GOP-by-GOP basis, rather than just staying permanently 
in 1080i25 (and using MBAFF to handle static/native progressive content).

I have tried before to raise a fault report but never managed to log in.

If I do a git checkout fixes/31 to go forward to current head how do I 
just eliminate that single change?

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