Thanks to pdr0 -at- shaw.ca, My quest for the (nearly perfect) p24-to-p60
transcode has concluded.
But remaining is an ffmpeg behavior that seems (to me) to be key to understanding ffmpeg
architecture, to wit: The characteristics of frame traversal through a filter chain.
From a prior topic:
-----
Filter graph:
split[A] select='not(eq(mod(n+1\,5)\,3))' [C]interleave
[B]split[D]select='eq(mod(n+1\,5)\,2)'[F]blend[D]
[E]select='eq(mod(n+1\,5)\,3)'[G]
What I expected/hoped:
split[A] 0 1 _ 3 4 [C]interleave 0 1 B 3 4 //5 frames
[B]split[D] _ 1 _ _ _ [F]blend[D] |
[E] _ _ 2 _ _ [G] blend of 1+2
What appears to be happening:
split[A] 0 1 _ 3 4 [C]interleave 0 1 _ 3 4 //4 frames
[B]split[D] _ _ _ _ _ [F]blend[D]
[E] _ _ 2 _ _ [G]
The behavior is as though because frame 1 (see Note) can take the [A][C] path, it does take it &
that leaves nothing left to also take the [B][D][F] path, so blend never outputs.
-----
(Note: I originally wrote "frame n+1==1" but that was an error.)
I assume that frame numbers are assigned at the input of the filter chain as frames are encountered,
and that the following actions occur.
Frame 0: Traverses [A][C] and is enqueued at [C].
Frame 1: Traverses [A][C] and is enqueued at [C] (see Proposition).
Frame 2: Traverses [B][E][G] and is enqueued at [G].
Frame 3: Traverses [A][C] and is enqueued at [C].
Frame 4: Traverses [A][C] and is enqueued at [C].
Proposition: Frame 1 could also traverse [B][D][F] and be enqueued at [F] but since it's already
enqueued at [C], it does not do so.
Specifically, it appears that ffmpeg does not recurse the filter chain for frames that are already
enqueued, thus Frame 1 is not enqueued at [F], thus 'blend' doesn't activate when Frame 2 arrives at
[G], thus Frame 2 is never enqueued at [D] and never appears in the output of 'interleave'.
Is what I've written correct? Authoritative confirmation or correction of this architectural detail
is desired.
Regards,
Mark.
_______________________________________________
ffmpeg-user mailing list
ffmpeg-user@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-user
To unsubscribe, visit link above, or email
ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
