[MPlayer-DOCS] RFC: mencoder with interlacing/telecine howto (draft 1)

[Corey Hickey]

D Richard Felker III wrote:
> On Sat, Jan 03, 2004 at 07:02:25PM -0800, Corey Hickey wrote:
> 
> It is possible (deinterlace to 60fps). However, such files will not
> compress well at all, and they'll take insane cpu power to decode. To
> make one you need to use -vf tfields, which is buggy with G1... :)
> 

I tried it out as I was writing the draft, but it kept crashing. I tried
a different source now, so I wrote a paragraph into the doc with a
warning.

> It also has interlaced motion vector support now too, which you should
> enable.

What is the option name? I couldn't find it in the manpage.

> 
> While you're mentioning cropping, crop height and offset must _always_
> be a multiple of 4 for 4:2:0 video. If not you'll mess it up bad.

Does it only have to be a multiple of 4 for interlaced/telecined video,
or do you mean that to apply to all 4:2:0?

> 
>>Filmdint
>>TODO: DESCRIBE FILMDINT (I haven't used filmdint yet, but it ought to be good)
> 
> 
> It's ok, but IMO it tries to deinterlace rather than doing inverse
> telecine too often (much like settop DVD players & progressive TVs)
> which gives ugly flickering and other artefacts. If you're going to
> use it, you at least need to spend some time tuning the options and
> watching the output first to make sure it's not messing up.
> 

Hoping you don't mind, I quoted this paragraph and attributed it to you.

>>--Mixed progressive and interlaced--
>>
>>There are two options for dealing with this category, each of which is a
>>compromise. You should decide based on the duration/location of each type.
>>
>>1. Treat it as progressive. The interlaced parts will look interlaced, and some
>>   of the interlaced frames will have to be dropped, resulting in a bit of
>>   uneven jumpiness. You can use a postprocessing filter if you want to, but it
>>   may adversely affect the progressive parts.
>>
>>2. Treat it as interlaced. Some frames of the progressive parts will need to be
>>   duplicated, resulting in uneven jumpiness. Again, deinterlacing filters may
>>   degrade the progressive parts.
> 
> 
> Yes, alas mencoder (G1) doesn't support variable-fps output. I would
> strongly recommend against option 1. The best approach (aside from
> using a different program to encode) would be to leave output at 29.97
> fps.

Why is option 1 so bad? It would seem to me to be a matter of what parts
you want to look best, and the relative proportions of each type. To me,
at least, the duplication of frames in 23.976 -> 29.97 looks just about
as the dropping of frames from 29.97 -> 23.976; that may just be a
personal preference, though.

> If the interlaced scenes are mostly low-motion, you could try -vf
> pp=lb or l5 and see if you think the output is acceptable. This will
> blend away the combing without throwing away half the picture, so it
> will temporally blur interlaced content, but on the other hand it
> won't do serious damage to progressive frames.

Now that I think about it, would it be out of the question to use pullup
to telecine the progressive content, deinterlace everything with -pp=lb,
and encode at 29.97? I know that will do slightly awful things to the
progressive parts, but when I'm watching a movie I tend to be distracted
more by what appear to be uneven framerates (from duplicated frames)
than by a bit of picture degradation. Back before you wrote detc I had
encoded a few telecined movies with pp=lb, and they didn't look
prohibitively bad.

> 
> Thanks for writing this doc, btw!
> 

No problem! Thank you for your input, too.

-Corey