On 2021-03-15 06:43, Paul B Mahol wrote:
On Sun, Mar 14, 2021 at 11:18 PM Mark Filipak (ffmpeg) wrote:
On 2021-03-14 10:47, Mark Filipak (ffmpeg) wrote:
I hoped that "marked as interlaced" [1] meant that
'select=expr=not(eq(interlace_type\,TOPFIRST)+eq(interlace_type\,BOTTOMFIRST))'
[2]
Have I made myself understood? Do you see the problem?
...progressive.&.scan-int.here... 'select' ...only.progressive.here...
But scan-interlace frames are getting through the 'select'.
Either,
1, 'select' is broken, or
2, 'fieldmatch' is broken, or
3, 'fieldmatch' is setting a different flag (not 'interlace_type').
4, Missing more than half of information to give actual correct conclusion.
I don't know what you mean, Paul, but unless there's features I don't know about,
'fieldmatch,yadif,decimate' is, by design, kind to telecined segments of video but unkind to
scan-interlaced segments.
Here are the facts as I know the facts.
'fieldmatch' pulls up 5-frame telecined segments while leaving frame 4 as a
duplicate of frame 3.
Since 'decimate=cycle=5' discards frame 4 in formerly telecined segments, 'FRAME_RATE' is reduced
(to 23.976fps).
Reducing 'FRAME_RATE' in formerly telecined segments also reduces 'FRAME_RATE' in scan-interlaced
segments unless either,
1, internal streams support VFR, or
2, scan-interlaced frames are 'split' out to a secondary stream prior to
'decimate'.
Apparently, internal streams don't support VFR [1], therefore, 'FRAME_RATE' in scan-interlaced
segments is reduced unless scan-interlaced frames are 'split' out.
Scan-interlaced frames can't be 'split' out [2], therefore, the 'FRAME_RATE' in scan-interlaced
segments are reduced.
Since 'FRAME_RATE' reduction in scan-interlaced segments can't be avoided, 1 out of 5
scan-interlaced frames are dropped [3] and video in those segments are be degraded.
[1] If serial ffmpeg streams supported VFR, then detelecined segments v. scan-interlaced segments
could be differentiated via 'FRAME_RATE'
[2] Though 'fieldmatch' flags scan-interlaced frames as 'interlaced', the flag is not 'select'able:
'select=expr=eq(interlace_type\,TOPFIRST)+eq(interlace_type\,BOTTOMFIRST)' always fails.
[3] Though follow-on deinterlacers (e.g. 'yadif') can be inserted between 'fieldmatch' & 'decimate',
doing so does not prevent 1-in-5 frame drops.
I understand what was intended, but what is happening is not what was intended -- the
scan-interlaced sections lose 1 frame in every 5 frames and thereby suffer some judder. The easiest
fix would probably be to make the 'interlaced' flag in note [2] visible to the 'select' filter.
Your comments are welcome.
Regards,
Mark.
How do I proceed?
would work. However, the 'select' doesn't work. I'm counting on the
'select' working -- not working
is a complete show stopper.
Is there some other species of "marked as interlaced" that will make the
'select' work?
Thanks,
Mark.
[1] From https://ffmpeg.org/ffmpeg-filters.html#fieldmatch
"The separation of the field matching and the decimation is notably
motivated by the possibility of inserting a de-interlacing filter
fallback between the two. If the source has mixed telecined and real
interlaced content, fieldmatch will not be able to match fields for
the interlaced parts. But these remaining combed frames will be
*marked as interlaced*, and thus can be de-interlaced by a later
filter such as yadif before decimation."
[2] From https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect
"interlace_type (video only)
" The frame interlace type. It can assume one of the following values:
" PROGRESSIVE
" The frame is progressive (not interlaced).
" TOPFIRST
" The frame is top-field-first.
" BOTTOMFIRST
" The frame is bottom-field-first."
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