Jtdylktuy

Working on a research project with a color system that alernates between red (R) and green (G) pictures. We want to try different modes to bring that material to the digital domain. For this we want to try various pull-down sequences.

We want to project in 48fps or 60 fps.

• Triple each frame: R1 R1 R1 G1 G1 G1


• Triple each frame2: R1 G1 R1 G1 R1 G1


• Insert black frame: R1 R1 R1 G1 G1 G1 BL


• Insert black frame2: R1 R1 R1 G1 G1 BL R2 R2 G2 G2 G2 BL


• Insert black frame3: R1 G1 BL R2 G2 BL


• Insert black frame4: R1 R1 BL G1 G1 BL

...and so on

Is this possible in ffmpeg?

The alternative is to write a simple script to copy and renumber an image sequence. Obviously, it would be faster and simpler to do it all from within ffmpeg.

Thank you for your help.

This can be carried out within ffmpeg using a series of filters.

There are two considerations:

a) change in number of frames, and

b) sequencing of frames

We'll use the fps filter to increase frame count. The filter will perform regular duplication to do this. Then the shuffleframes filter to achieve the sequence rearrangement required. We'll also need drawbox filter to generate black frames, if needed. These sequences can be output at any frame rate.

We will ingest each image sequence at 1 fps as this makes calculations simpler.

For

Triple each frame: R1 R1 R1 G1 G1 G1

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=3,settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

The fps filter is used to triple the count of each frame. Due to how the fps filter works, we need to reset the stream timebase to get enough resolution for the next steps. It is set to AVTB i.e. 1/1000000 seconds. Then the frames are renumbered at 1/48th seconds intervals. Finally, the output framerate is set to 48.

Triple each frame2: R1 G1 R1 G1 R1 G1

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=3,shuffleframes=0 3 0 3 0 3,settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

The fps triples each frame so 0 3 0 3 0 3 outputs six frames using the first copy of R1 and G1.

Insert black frame: R1 R1 R1 G1 G1 G1 BL

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=4,shuffleframes=0 0 0 4 4 4 4 -1,drawbox=t=fill:enable=not(mod(n+1,7)),settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

Here we quadruple each frame, then use shuffle to keep 7 out of each 8 frames, dropping the last one. Then use drawbox with enable to make each 7th frame black (t=fill draws a solid box. Default color is black).

Insert black frame2: R1 R1 R1 G1 G1 BL R2 R2 G2 G2 G2 BL

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=3,shuffleframes=0 0 3 3 3 3:enable='mod(floor(n/6),2)',drawbox=t=fill:enable=not(mod(n+1,6)),settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

Slightly trickier. shguffleframes only needs to applied to each alternate set of 6 frames. We use timeline editing i.e. enable option for that.

Insert black frame3: R1 G1 BL R2 G2 BL

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=2,shuffleframes=0 2 2 -1,drawbox=t=fill:enable=not(mod(n+1,3)),settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

Double frame count and keep 3 frames, drawing black on 3rd and dropping 4th.

Insert black frame4: R1 R1 BL G1 G1 BL

ffmpeg -framerate 1 -i frames%04d.jpg -vf "fps=3,drawbox=t=fill:enable=not(mod(n+1,3)),settb=AVTB,setpts=N/48/TB" -r 48 -y out.mp4

Simple. Just make each 3rd frame black.

Not only is it possible, it is alsoe easy and efficient: Use a concat file

Assuming you have your frames in r1.png, ... g2.png etc. and 48 Hz (so a 20.8333.. ms timebase) a concat file fragment of

file 'r1.png'

duration 0.0625

file 'g1.png'

duration 0.0625

will give 3 red1 frames, then 3 green1 frames (20.8333..*3=62.5)

With these kinds of fragments you can build whatever sequence you need, then run

ffmpeg -i /path/to/concatfile -c.... /path/to/outfile

To create your clip.