I am not getting the final image results I need when layering together multiple mp4s of the same length and format into a single output MP4. I am using ffmpeg to create a pseudo 'motion blur' effect on animation, and need to layer mp4s together with identical opacities to produce the final video.
I am using a base 'black' MP4 as the first layer for a background, and then adding a series of source mp4s with equal opacity over the top in each pass. Here I am showing a photoshop mockup using their 'normal' blending mode which is exactly the blending effect I am trying to replicate with ffmpeg. I understand that the final composite is less "bright" but that's fine (unless you have any ideas).
Instead of looking like the result above, I am getting output where the colors are either all pink, garbled, super dark or generally hugely overbright etc based on trying different blend modes.
Here are the commands I am using:
To create the original (uncompressed?) 'black' MP4 from a sequence of black pngs:
ffmpeg -start_number 0 -r 24 -f image2 -s 1920x1080 -i black_seq.%04d.png -vcodec libx264 -crf 0 -pix_fmt yuv420p black_seq.mp4 -y
I then take that "black_seq.mp4" and blend a set of n number of source mp4s over the top with an opacity value. This runs in a loop and the output.mp4 of each pass becomes the input.mp4 of the next pass until it completes. In this example a total of 10 source mp4s assigns their opacity to 0.1 for each pass, and this is a single pass (below). The source mp4s are all very similar in their appearance and color, essentially just the same sequence of animation but offset in time by fractions of a single frame and have been generated from color pngs, using the same code that produced the first black layer (above).
ffmpeg i input.mp4 -i n_layer.mp4 -vcodec libx264 -crf 0 -pix_fmt yuv420p -filter_complex "blend=all_mode='overlay':all_opacity=0.1" output.mp4 -y
Then finally add some compression to the result as the final "blur.mp4"
ffmpeg -i "output.mp4" -vcodec libx264 -crf 25 -pix_fmt yuv420p "blur.mp4" -y
And yes, this is certainly highly inefficient as an approach, but I am learning. The main issue I am trying to solve is, despite the final blur.mp4 being less "bright", it has colors that are not matching the original animation and instead looks like the animation has been hue shifted somehow.
This image shows a cropped output for comparison (the processed blur is set to zero for clarity)
I would love some insight.
