[mythtv] [mythtv-commits] Ticket #2429: Autodetect video scan is confused by 1080i recordings

Yeasah Pell yeasah at schwide.com
Wed Sep 20 18:35:44 UTC 2006

Jack Perveiler wrote:
> --- Kevin Kuphal <kuphal at dls.net> wrote:
>> MythTV wrote:
>>> #2429: Autodetect video scan is confused by 1080i recordings
> <snip>
>>> Changes (by ijr):
>>>   * status:  new => closed
>>>   * resolution:  => wontfix
>>> Comment:
>>>  That's normal.
>> Normal?  I have to manually set all my NBC HD recordings to Interlaced 
>> whenever I watch them because of this.  It doesn't seem to be desired 
>> behavior...
>> Kevin
> I get this a lot on my PBS and NBC HD recordings too.  What would be nice would
> be a per-channel setting for video-scan (feature request without a patch). 
> Make the default be "detect", but allow setting an override in the channel
> editor.
> I THOUGHT I read that Daniel was doing SOMETHING like this in the vid branch,
> but I've never looked into it so I don't know.
> If I'm wrong about the vid branch and nobody else implements this I may take a
> crack at it next week when my wife+kid are out of town.
> --Jack
I also get this a lot, on all sorts of channels -- both HD and SD. 
There's always some combination of filters and interlace settings that 
works, but it can be extremely tedious to change all that around for 
different programs. It's not a per-channel thing either, it's dependent 
on however the content was produced, so being able to change these 
things on a per-channel basis would not totally solve the problem.

Animated material is often done at 24fps and telecined (as are most 
movies that are broadcast), and the only way I can get that kind of 
material to play without unnecessary interlacing artifacts or having the 
video-scan detection go berserk is to include "ivtc" in the filter 
chain, as well as an appropriate deinterlacer, and force video scan to 
interlaced mode. (I know ivtc was primarily added to myth to allow DVDs 
to be inverse telecined, but it does seem to work for some kinds of 
broadcast material as well.)

Other times ivtc totally hoses the video though (causing severe 
jerking), it doesn't seem to be doing sufficient cadence detection -- so 
leaving that in isn't really an option. It's a real pain to have to 
change that setting, since it involves changing text in a buried submenu.

Basically, I don't think myth currently has what you would call a 
complete solution for deinterlacing broadcast content -- or if it does, 
I have no idea how to enable it. It needs to be able to robustly detect 
any telecine cadence (which can be hard, since there are crazy cadences 
out there, bad edits can cause the sequence to become discontinous, 
etc.), run an appropriate inverse telecine when it is needed, and then 
finally deinterlace frames as required based on all that using the 
deinterlacing method selected by the user.

Most digital TVs are capable of all this -- telecine pulldown and 
adaptive deinterlacing is getting more common these days (my TV does do 
this, anyway.) I'd like to be able to set things up so that my frontend 
output in the appropriate interlaced mode (via the xrandr frontend 
options) when playing interlaced content and let the TV do the 
deinterlacing, but I haven't found how to set it up so that it works 
with the diverse set of broadcast content out there (lots of different 
resolutions and frame rates) -- in any case, that option is a "punt to 
TV" option, whereas it would be much better if mythtv itself was at 
least as capable as a modern TV at handling interlaced content.

Anyway, that's how I read ticket #2429, as a feature request for robust 
handling of interlaced/telecined content.

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