[FFmpeg-user] "interlace"

[Mark Filipak]

On 09/06/2020 04:16 PM, Edward Park wrote:
> Hi,
> 
>> 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.
> That's more or less what a participle is.
> 
>> 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.
> 
> Is it? Hard telecine is like telecining film and then recording it on a VCR, isn't it? And you don't need to deinterlace interlaced video to display it on an interlaced scanning TV. I think the confusion is when you deinterlace interlaced video, it is still interlaced video (or at least I think of it that way).
> 
> Regards,
> Ted Park

"interlace [transitive verb]: 1. To connect by or as if by lacing together; interweave. 2. To 
intersperse; intermix: 'interlaced lies with truth'. [intransitive verb]: To intertwine."

The word "interlaced" is universally applied to scan fields. Scan fields are not interlaced. The 
lines are aggregated into odd and even fields (i.e. blocks at the macroblock level) but the rows 
("lines" if you will) are not interlaced. Scan fields are interleaved, but that is not interlacing. 
If anything, that is deinterlacing.

Given the historic misuse of "interlace", I will continue to use alternatives. The best alternative 
is "field-based". Next is "unweaved". Also acceptable is "interleaved" because that aptly describes 
the condition of the fields.