[mythtv] Perfect sync to interlaced TVs

[Maatt]

Good thinking. I wonder if someone has thought of it before.
I wonder what the sound would be like 20ms out. In fact you could
probably advance the sound 10ms so its only +/-10ms out.

Are you going to implement it? I'm tempted to have a go.

Matt.


On Wed, Sep 24, 2008 at 7:06 PM, Paul Gardiner <lists at glidos.net> wrote:
> I have an idea for an alternative form of interlacing to achieve
> perfect sync for interlaced content played on interlaced TVs. In
> theory the best picture is achieved if the interlaces are displayed
> as is, with no processing, but there are problems in doing so
> in MythTV.
>
> Here's some notaton:
>
> [i/j] means a frame consisting of field i in odd position, and field
> j in even position being presented to the output stage.
>
> i/    means the output stage displaying field i in odd position.
>
> /j    means the output stage displaying field j in even postion.
>
>
>
> Here's what you get when all is synced correctly.
>
>   [1/2] 1/ /2 [3/4] 3/ /4 [5/6] 5/ /6
>
>
>
> Here's what you get when the frame presentation is synced to the
> wrong vsync pulse.
>
>   [1/2] /2 1/ [3/4] /4 3/ [5/6] /6 5/
>
> That looks awful because the fields appear out of order. It
> give really bad comb-teeth ghosting.
>
>
>
> Here's what you get by using bob deinterlacing, when all is
> synced correctly.
>
>   [1/1] 1/ [2/2] /2 [3/3] 3/ [4/4] /4 [5/5] 5/ [6/6] /6
>
>
>
> Here's what you get with bob deinterlacing incorrectly synced
> (I have to admit I've never seen evidence of this happening, but
> it should be the case).
>
>   [1/1] /1 [2/2] 2/ [3/3] /3 [4/4] 4/ [5/5] /5 [6/6] 6/
>
> The fields are displayed in the correct order, but the odd fields
> are displayed in even position and the even in odd.
>
>
>
> Here's what you would get with the deinterlacing I'm proposing
> (call it adjacent pairing maybe). First the correctly synced
> version.
>
>   [1/2] 1/ [3/2] /2 [3/4] 3/ [5/4] /4 [5/6] 5/
>
>
>
> And here's what you get with adjacent pairing when badly synced.
>
>   [1/2] /2 [3/2] 3/ [3/4] /4 [5/4] 5/ [5/6] /6
>
> Note you still get the correct order and positioning of fields,
> just all offset by a 50th of a second.
>
>
>
> Is this of any use?
>
> Paul.
>
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