[FFmpeg-user] "interlace"

Mark Filipak markfilipak.windows+ffmpeg at gmail.com
Sun Sep 6 22:26:57 EEST 2020

Admittedly, this is an anal-compulsive topic. But good documentation often requires anal compulsion. 
Good documentation definitely requires thorough knowledge of language usage.

The topic is use of the various forms of the word "interlace". But I'm going to use the word "build" 
as an example because it has more, and more varied cases.

"Let's build it" -- "build" as a verb.
"We will be building it" employs "build" as a present participle.
"Assemble the building crew" is the present participle used as an adjective (the crew is actively 
engaged in building something, so it is the "building crew" as opposed to some other "crew").
"It's a tall building" employs "build" as a verbal noun.
"Assemble the building's crew" is the verbal noun used as a possessive adjective (the crew is 
associated with "the building" as opposed to some other crew that's not associated with "the 
building") in the same way that "the cat's meow" uses the ordinary noun, "cat", as a possessive 

In the case of "interlace":
"It's interlaced video" -- video in which the lines alternate (i.e. are interlaced) between two (or 
theoretically, more) fields (e.g. odd-even-odd-even...). That employs the past participle of the 
verb, "interlace", as an adjective to modify "video".

H.262 refers to "interlace video" when referring to hard telecine. But "interlace video" is a bit of 
a mutt. "Interlace" is clearly being used as an adjective, yet "interlace" is not a participle (past 
or present) -- "interlaced" is the past participle and "interlacing" is the present participle. What 
it would have to be is a verbal adjective (i.e. a verb used as an adjective). I may be wrong, but I 
don't think there exists such a thing as a verbal adjective.

A hard telecined video residing on a disc is clearly not interlaced. It is clearly deinterlaced 
(i.e. stored in fields). Since it is deinterlaced, it can be fed directly to a scanning TV (i.e. 
CRT) provided it is of the proper frame rate, or it can be interlaced -- a verb -- by a decoder as 
part of the decoding step.

Conclusion: Employing the past participle, "interlaced", to a field-based video stream is just plain 
wrong. All of the ffmpeg documentation that uses the word "interlaced" should be checked for accuracy.
Racism is like roaches. When you switch on the light, they scurry.
But if you don't switch on the light, you don't know they're there.

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