This IS the Avid L2: Re: [Avid-L2] Best method of converting a 23.976 file and or Avid timeline to 29.97P file?

Monday, November 9, 2015

Re: [Avid-L2] Best method of converting a 23.976 file and or Avid timeline to 29.97P file?

In *progressive* HD, both fields are at "the same moment in time".

As I said, I used *interlaced* HD footage for my test, otherwise I wouldn't have seen the shuddering I described when I changed the field order.

So, in case you weren't aware, HD can be progressive (e.g. 720p), interlaced (e.g. 1080i) - and it can be psf too.

If the fields in HD were only ever "of the same moment in time", then pulldown wouldn't work.

On 9 November 2015 at 13:29, John Pale <pale.edit@gmail.com> wrote:

Forgive my ignorance, but is what you describe because in HD the fields are of the same moment in time? In SD, I am pretty sure you get aliasing with incorrect field order. In SD, there is a measurable delay between field 1 and 2. Of course, I could be completely off the charts wrong about this.

On Monday, November 9, 2015, David Ross speckydave@gmail.com [Avid-L2] <Avid-L2@yahoogroups.com> wrote:

Just tested this on a broadcast monitor by adding a big diagonal line across some upper-field HD footage. Exported as QuickTime ProRes upper-field, which I them imported into Premiere and played back: smooth motion and no aliasing while interpreted as upper-field. When I switched the interpretation to lower-field, I got all the horrible shuddering from fields being played in the wrong order, but the static diagonal line showed no aliasing at all.

I would say your assumption about fields being re-positioned is wrong. When someone mis-interprets upper-field-first footage as lower-field-first, they just get the fields played in the wrong order. That's it. No re-positioning. Just (in this case) the lower field played first, then the upper field.
I would have thought that to take the upper field and shift it down a line to the lower field position and vice versa would be quite a deliberate process. I can't right now think of a way to *accidentally* tell the system to actually reposition the fields like this (though since there generally tends to be a way to easily screw anything up, I don't doubt that it can be done with a single bad keystroke...).

D.

On 9 November 2015 at 01:24, bigfish@pacbell.net [Avid-L2] <Avid-L2@yahoogroups.com> wrote:

If the fields are in reverse order then they are not playing in the same field the are intended for. Think of a diagonal line. I am assuming that with wrong field order Field 2 plays first and is positioned on the lines intended for Field 1 and Field 1 plays second in the lines intended for Field 2. That would mean the horizontal scan lines are inverted too. To me that would create the stair stepping even on a static frame.