[FFmpeg-user] propagation of frames in a filter complex

[Ted Park]

Hey,

> 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 n+1==1 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.
> 
> I've used 'datascope' in various parts of the filter graph in an attempt to confirm this on my own. It's difficult because my test video doesn't display frame #s.
> 
> If that indeed is the behavior, then ...
> 
> I need a way to duplicate a frame, # n+1%5==1 in this case, so that the 'blend' operates.

Huh, I didn't know you could reuse filter pad labels. I've translated the graph2dot output to svg, it doesn't look like it'll help much though.
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I think graphmonitor would be more helpful for this kind of split-chained-to-split complex graph.
But I think you could use the multiple output option for select filter, where you use the value to select which pad the frame gets sent to. (It isn't evaluated as a boolean in that case, so if value is 3.??? it goes to output pad 3, if it's 0.??? it goes to 0, etc)

Regards,
Ted Park