On 04/19/2020 12:26 AM, pdr0 wrote:
Mark Filipak wrote
Deinterlacing does not necessarily have to be used in the context of
"telecast". e.g. a consumer camcorder recording home video interlaced
content is technically not "telecast". Telecast implies "broadcast on
television"
You are right of course. I use "telecast" (e.g., i30-telecast) simply to
distinguish the origin of
scans from hard telecines. Can you suggest a better term? Perhaps
"i30-camera" versus "i30"? Or
maybe the better approach would be to distinguish hard telecine: "i30"
versus "i30-progressive"? Or
maybe distinguish both of them: "i30-camera" versus "i30-progressive"?
Some home video cameras can shoot native progressive modes too - 24p ,
23.976p. Some DV cameras shoot 24p advanced pulldown or standard.
So why not use a descriptive term for what it actually in terms of content,
and how it's arranged or stored? (see below)
I would adopt a descriptive term for myself, but I fear that ordinary people would find it difficult
to understand and remember.
The simplest operational definition is double rate deinterlacing
separates
and resizes each field to a frame +/- other processing. Single rate
deinterlacing does the same as double, but discards either even or odd
frames (or fields if they are discarded before the resize)
I think I understand your reference to "resize": line-doubling of
half-height images to full-height
images, right?
"Resizing " a field in this context is any method of taking a field and
enlarging it to a full sized frame. There are dozens of different
algorithms. Line doubling is one method, but that is essentially a "nearest
neighbor" resize without any interpolation. That's the simplest type. Some
complex deinterlacers use information from other fields to fill in the
missing information with adaptive motion compensation
I would love to use motion compensation but I can't, at least not with ffmpeg. Now, if there was
such a thing as smart telecine...
A A A+B B B -- input
A A B B -- pass 4 frames directly to output
A A+B B -- pass 3 frames to filter
X -- motion compensated filter to output
Unfortunately, ffmpeg can't do that because ffmpeg does not recurse the filter complex. That is,
ffmpeg can pass the 2nd & 4th frames to the output, or to the filter, but not both.
But I don't understand how "double rate" fits in. Seems to me that fields
have to be converted
(resized) to frames no matter what the "rate" is. I also don't understand
why either rate or
double-rate would discard anything.
The "rate" describes the output frame rate.
Of course.
Double rate deinterlacing keeps all the temporal information. Recall what
"interlace content" really means. It's 59.94 distinct moments in time
captured per second . In motion you have 59.94 different images.
That may be true in general, but the result of 55-telecine is
A A A+B B B ... repeat to end-of-stream
So there aren't 59.94 distinct moments. There're only 24 distinct moments (the
same as the input).
Single rate deinterlacing drops 1/2 the temporal information (either even,
or odd fields are retained)
single rate deinterlace: 29.97i interlaced content => 29.97p output
double rate deinterlace: 29.97i interlaced content => 59.94p output
There is no 29.97i interlaced content. There's p24 content (the source) and p60 content that combs
frames 2 7 12 17 etc. (the transcode).
Okay, by "deinterlace" you mean what I mean by "combing". Let's see:
A B B+C C+D D ... repeat to end-of-stream == p30
A A B B B+C B+C C+D C+D D D ... repeat to end-of-stream == p30x2
A A A+B B B C C C+D D D ... repeat to end-of-stream == p60
Sorry, my friend, I just don't see any temporal information missing.
I know you meant telecine up conversion of 23.976p to 29.97i (not "p").
But
other framerates can be telecined eg. An 8mm 16fps telecine to 29.97i.
Well, when I've telecined, the result is p30, not i30. Due to the presence
of ffmpeg police, I
hesitate to write that ffmpeg outputs only frames -- that is certainly
true of HandBrake, though.
When I refer to 24fps and 30fps (and 60fps, too) I include 24/1.001 and
30/1.001 (and 60/1.001)
without explicitly writing it. Most ordinary people (and most BD & DVD
packaging) don't mention or
know about "/1.001".
The result of telecine is progressive content (you started with progressive
content) , but the output signal is interlaced.
According to the Motion Pictures Experts Group, it's not interlaced because the odd/even lines are
not separated by 1/fieldrate seconds; they are separated by 1/24 sec.
That's the reason for
telecine in the first place - that 29.97i signal is required for equipment
compatibility. So it's commonly denoted as 29.97i . That can be confusing
because interlaced content is also 29.97i. That's why /content/ is used to
describe everything .
Once again, this is a terminology problem. You are one person who acknowledges that terminology
problems exist, and that I find heartening. Here's how I have resolved it:
I call a 30fps stream that's 23-telecined from p24, "t30" -- "t" for "telecine".
I call a 30fps stream that's 1/fieldrate interlaced, "s30" -- "s" for "scan"
(see Note).
I call a 60fps stream that's 23-telecined, then frame doubled, "t30x2".
I call a 60fps stream that's 55-telecined from p24, "t60".
Note: I would have called this "i30", but "i30" is already taken.
Now, the reason I write "p24" instead of "24p" -- I'm not the only person who does this -- is so it
fits an overall scheme that's compact, but that an ordinary human being can pretty much understand:
16:9-480p24 -- this is soft telecine
4:3-480t30 -- this is hard telecine
16:9-1080p24
I'm not listing all the possible combinations of aspect ratio & line count & frame rate, but you
probably get the idea.
When I'm lazy I use 23.976p notation (but it really means 24000/1001) ,
because 24.0p is something else - for example, there are both 24.0p and
23.976p blu-ray and they are different frame rates . Similarly, I use
"29.97" (but it really means 30000/1001), because "30.0" is something else.
You can have cameras or web video as 30.0p. Both exist and are different and
should be differentiated otherwise you have time and sync issues
I use 24/1.001 because it's shorter. Then, unless it really, really matters, I use 24. So, who's
lazier? You or me? ;-)...Me! Me! Me!
"Combing" is just a generic, non-specific visual description. There can
be
other causes for "combing". eg. A warped film scan that causes spatial
field
misalignment can look like "combing". Interlaced content in motion , when
viewed on a progressive display without processing is also described as
"combing" - it's the same underlying mechanism of upper and lower field
taken at different points in time
Again, good points. May I suggest that when I use "combing" I mean the
frame content that results
from a 1/24th second temporal difference between the odd lines of a
progressive image and the even
line of the same progressive image that results from telecine? If there's
a better term, I'll use
that better term. Do you know of a better term?
I know what you're trying to say , but the term "combing" , it's appearance,
and underlying mechanism is the same. This is how the term "combing" is
currently used in both general public and industry professionals. If you
specifically mean combining on frames from telecine , then you should say so
, otherwise you will confuse many people.
You know this already - there is an important distinction between the actual
underlying video, but on a single frame or 2 field examination you will not
see that. You need to either 1) separate the fields and examine the field
pattern over a range with motion or 2) double rate deinterlace and examine
the pattern over a range with motion . This is how you determine what the
content actually is, whether it's interlaced or progressive
Erm... I'm not analyzing a mystery video. I'm transcoding from a known source. I know what the
content actually is.
Decombing is smoothing combed frames.
Yes, but this is an ambiguous term. "Decombing" can imply anything from
various methods of deinterlacing to inverse telecine / removing pulldown
.
To the best of my knowlege, ffmpeg doesn't use the terms "combing" or
"decombing" -- certainly
there's no decomb filter. I don't have a term that distinguishes smoothing
of a 1/24th second comb
(what I call "decombing") from smoothing of a 1/60th second (or 1/50th
second) comb that results
from deinterlace (which I don't call "decombing"). Can you suggest a term
for the latter? Or terms
for the both of them?
Why do you need a specific "term?"
To facilitate communication and understanding.
There are dozens of processing algorithms (not just talking about ffmpeg).
There are many ways to "decomb" something . The one you ended up using is
categorized as a blend deinterlacer because the top and bottom field are
blended with each other. If you examine the separated fields , the fields
are co-mingled, no longer distinct. You needed to retain both fields for
your purpose
No, I don't. I don't want to retain both fields. I want to blend them. That's what
'pp=linblenddeint' does, and that's why I'm happy with it.
There is no distinction in terms of distribution of application for this
type of filter. You put the distinction on filtering specific frames by
using select. You could apply blend deinterlace to every frame too (for
interlaced content) - how is that any different visually in terms of any
single frame there vs. your every 5th frame ?
I honestly don't know. What I do know is if I pass select='not(eq(n+1\,5)\,3))' to the output
unaltered but I filter select='eq(n+1\,5)\,3)',pp=linblenddeint before the output, the video looks
better on a 60Hz TV. I don't want to pass the progressive frames through 'pp=linblenddeint'.
You could have used a different filter, maybe a box blur , applied on the
same frame selection . Would you still call that "decomb" ?
Yes, but only because I call the original frame "combed".
I think I'll call telecine "combed" frames "t-combed" and the combing that results from interlacing
odd & even fields "i-combed".
Regarding inverse telecine (aka INVT), I've never seen INVT that didn't
yield back uncombed, purely
progressive pictures (as "picture" is defined in the MPEG spec). Can
you/will you enlighten me
because it's simply outside my experience.
It happens all the time. This is simply reversing the process. Inverse
telecine is the same thing as "removing pulldown". You get back the original
progressive frames you started with.
Okay, that's what I thought. Since INVT produces the original p24, it's not combed. I thought you
said that inverse telecine can produce combing. My bad. :)
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