[FFmpeg-user] When to determine frames are progressive or interlaced ?

[Carl Eugen Hoyos]

Roger Pack <rogerdpack2 <at> gmail.com> writes:

> On 12/19/12, Carl Eugen Hoyos <cehoyos <at> ag.or.at> wrote:
> > tank pranav <akshar_tank <at> yahoo.com> writes:
> >
> >> I would like to know when to determine frames are
> >> progressive or interlaced ?

> > (Depending on how you define "interlaced" frames:)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Reading the whole thread, this may have been missed by some.

> > To the best of my knowledge, only visual inspection
> > tells you, but there is a filter named "idet" that
> > tells you if the video is interlaced.
> 
> I have no real idea, but I thought I saw once that MPEG picture
> headers mentioned if the picture was interlaced

Yes.
Unfortunately, the information is completely useless if you 
want to know if the *content* of he MPEG picture is 
interlaced.
I consider this the only relevant information. you can get 
it with -vf idet (it works very well here, if you have a 
failing sample, please provide it) or by visual inspection.

Other people may be interested in different things (like 
for example if the "MPEG picture headers" indicate 
interlaced or progressive), FFmpeg provides this information 
internally, if you want it to show, please provide samples 
(I can't implement things without samples) or implement it 
yourself (it is trivial).

And please note that you can not only encode 24/25 fps 
progressive material, changing the framerate to 50, throwing 
away every second field and call the result "interlaced" 
(it simply isn't afaict and that is what all - ? - television 
providers do afaik), but you can of course encode interlaced 
material as "progressive" (with a low quantiser there will be 
no visual quality loss). This is what FFmpeg does if you do 
not provide special flags.

Carl Eugen